Ever since the introduction of pid namespaces, procfs has had very implicit behaviour surrounding them (the pidns used by a procfs mount is auto-selected based on the mounting process's active pidns, and the pidns itself is basically hidden once the mount has been constructed).
/* pidns mount option for procfs */
This implicit behaviour has historically meant that userspace was required to do some special dances in order to configure the pidns of a procfs mount as desired. Examples include:
* In order to bypass the mnt_too_revealing() check, Kubernetes creates a procfs mount from an empty pidns so that user namespaced containers can be nested (without this, the nested containers would fail to mount procfs). But this requires forking off a helper process because you cannot just one-shot this using mount(2).
* Container runtimes in general need to fork into a container before configuring its mounts, which can lead to security issues in the case of shared-pidns containers (a privileged process in the pidns can interact with your container runtime process). While SUID_DUMP_DISABLE and user namespaces make this less of an issue, the strict need for this due to a minor uAPI wart is kind of unfortunate.
Things would be much easier if there was a way for userspace to just specify the pidns they want. Patch 1 implements a new "pidns" argument which can be set using fsconfig(2):
fsconfig(procfd, FSCONFIG_SET_FD, "pidns", NULL, nsfd); fsconfig(procfd, FSCONFIG_SET_STRING, "pidns", "/proc/self/ns/pid", 0);
or classic mount(2) / mount(8):
// mount -t proc -o pidns=/proc/self/ns/pid proc /tmp/proc mount("proc", "/tmp/proc", "proc", MS_..., "pidns=/proc/self/ns/pid");
The initial security model I have in this RFC is to be as conservative as possible and just mirror the security model for setns(2) -- which means that you can only set pidns=... to pid namespaces that your current pid namespace is a direct ancestor of and you have CAP_SYS_ADMIN privileges over the pid namespace. This fulfils the requirements of container runtimes, but I suspect that this may be too strict for some usecases.
The pidns argument is not displayed in mountinfo -- it's not clear to me what value it would make sense to show (maybe we could just use ns_dname to provide an identifier for the namespace, but this number would be fairly useless to userspace). I'm open to suggestions. Note that PROCFS_GET_PID_NAMESPACE (see below) does at least let userspace get information about this outside of mountinfo.
Note that you cannot change the pidns of an already-created procfs instance. The primary reason is that allowing this to be changed would require RCU-protecting proc_pid_ns(sb) and thus auditing all of fs/proc/* and some of the users in fs/* to make sure they wouldn't UAF the pid namespace. Since creating procfs instances is very cheap, it seems unnecessary to overcomplicate this upfront. Trying to reconfigure procfs this way errors out with -EBUSY.
/* ioctl(PROCFS_GET_PID_NAMESPACE) */
In addition, being able to figure out what pid namespace is being used by a procfs mount is quite useful when you have an administrative process (such as a container runtime) which wants to figure out the correct way of mapping PIDs between its own namespace and the namespace for procfs (using NS_GET_{PID,TGID}_{IN,FROM}_PIDNS). There are alternative ways to do this, but they all rely on ancillary information that third-party libraries and tools do not necessarily have access to.
To make this easier, add a new ioctl (PROCFS_GET_PID_NAMESPACE) which can be used to get a reference to the pidns that a procfs is using.
Rather than copying the (fairly strict) security model for setns(2), apply a slightly looser model to better match what userspace can already do:
* Make the ioctl only valid on the root (meaning that a process without access to the procfs root -- such as only having an fd to a procfs file or some open_tree(2)-like subset -- cannot use this API). This means that the process already has some level of access to the /proc/$pid directories.
* If the calling process is in an ancestor pidns, then they can already create pidfd for processes inside the pidns, which is morally equivalent to a pidns file descriptor according to setns(2). So it seems reasonable to just allow it in this case. (The justification for this model was suggested by Christian.)
* If the process has access to /proc/1/ns/pid already (i.e. has ptrace-read access to the pidns pid1), then this ioctl is equivalent to just opening a handle to it that way.
Ideally we would check for ptrace-read access against all processes in the pidns (which is very likely to be true for at least one process, as SUID_DUMP_DISABLE is cleared on exec(2) and is rarely set by most programs), but this would obviously not scale.
I'm open to suggestions for whether we need to make this stricter (or possibly allow more cases).
Signed-off-by: Aleksa Sarai cyphar@cyphar.com --- Changes in v4: - Remove unneeded EXPORT_SYMBOL_GPL. [Christian Brauner] - Return -EOPNOTSUPP for new APIs for CONFIG_PID_NS=n rather than pretending they don't exist entirely. [Christian Brauner] - PROCFS_IOCTL_MAGIC conflicts with XSDFEC_MAGIC, so we need to allocate subvalues more carefully (switch to _IO(PROCFS_IOCTL_MAGIC, 32)). - Add some more selftests for PROCFS_GET_PID_NAMESPACE. - Reword argument for PROCFS_GET_PID_NAMESPACE security model based on Christian's suggestion, and remove CAP_SYS_ADMIN edge-case (in most cases, such a process would also have ptrace-read credentials over the pidns pid1). - v3: https://lore.kernel.org/r/20250724-procfs-pidns-api-v3-0-4c685c910923@cyphar.com
Changes in v3: - Disallow changing pidns for existing procfs instances, as we'd probably have to RCU-protect everything that touches the pinned pidns reference. - Improve tests with slightly nicer ASSERT_ERRNO* macros. - v2: https://lore.kernel.org/r/20250723-procfs-pidns-api-v2-0-621e7edd8e40@cyphar.com
Changes in v2: - #ifdef CONFIG_PID_NS - Improve cover letter wording to make it clear we're talking about two separate features with different permission models. [Andy Lutomirski] - Fix build warnings in pidns_is_ancestor() patch. [kernel test robot] - v1: https://lore.kernel.org/r/20250721-procfs-pidns-api-v1-0-5cd9007e512d@cyphar.com
--- Aleksa Sarai (4): pidns: move is-ancestor logic to helper procfs: add "pidns" mount option procfs: add PROCFS_GET_PID_NAMESPACE ioctl selftests/proc: add tests for new pidns APIs
Documentation/filesystems/proc.rst | 12 ++ fs/proc/root.c | 166 +++++++++++++++- include/linux/pid_namespace.h | 9 + include/uapi/linux/fs.h | 4 + kernel/pid_namespace.c | 22 ++- tools/testing/selftests/proc/.gitignore | 1 + tools/testing/selftests/proc/Makefile | 1 + tools/testing/selftests/proc/proc-pidns.c | 315 ++++++++++++++++++++++++++++++ 8 files changed, 514 insertions(+), 16 deletions(-) --- base-commit: 66639db858112bf6b0f76677f7517643d586e575 change-id: 20250717-procfs-pidns-api-8ed1583431f0
Best regards,
This check will be needed in later patches, and there's no point open-coding it each time.
Signed-off-by: Aleksa Sarai cyphar@cyphar.com --- include/linux/pid_namespace.h | 9 +++++++++ kernel/pid_namespace.c | 22 ++++++++++++++-------- 2 files changed, 23 insertions(+), 8 deletions(-)
diff --git a/include/linux/pid_namespace.h b/include/linux/pid_namespace.h index 7c67a5811199..17fdc059f8da 100644 --- a/include/linux/pid_namespace.h +++ b/include/linux/pid_namespace.h @@ -84,6 +84,9 @@ extern void zap_pid_ns_processes(struct pid_namespace *pid_ns); extern int reboot_pid_ns(struct pid_namespace *pid_ns, int cmd); extern void put_pid_ns(struct pid_namespace *ns);
+extern bool pidns_is_ancestor(struct pid_namespace *child, + struct pid_namespace *ancestor); + #else /* !CONFIG_PID_NS */ #include <linux/err.h>
@@ -118,6 +121,12 @@ static inline int reboot_pid_ns(struct pid_namespace *pid_ns, int cmd) { return 0; } + +static inline bool pidns_is_ancestor(struct pid_namespace *child, + struct pid_namespace *ancestor) +{ + return false; +} #endif /* CONFIG_PID_NS */
extern struct pid_namespace *task_active_pid_ns(struct task_struct *tsk); diff --git a/kernel/pid_namespace.c b/kernel/pid_namespace.c index 7098ed44e717..b7b45c2597ec 100644 --- a/kernel/pid_namespace.c +++ b/kernel/pid_namespace.c @@ -390,11 +390,23 @@ static void pidns_put(struct ns_common *ns) put_pid_ns(to_pid_ns(ns)); }
+bool pidns_is_ancestor(struct pid_namespace *child, + struct pid_namespace *ancestor) +{ + struct pid_namespace *ns; + + if (child->level < ancestor->level) + return false; + for (ns = child; ns->level > ancestor->level; ns = ns->parent) + ; + return ns == ancestor; +} + static int pidns_install(struct nsset *nsset, struct ns_common *ns) { struct nsproxy *nsproxy = nsset->nsproxy; struct pid_namespace *active = task_active_pid_ns(current); - struct pid_namespace *ancestor, *new = to_pid_ns(ns); + struct pid_namespace *new = to_pid_ns(ns);
if (!ns_capable(new->user_ns, CAP_SYS_ADMIN) || !ns_capable(nsset->cred->user_ns, CAP_SYS_ADMIN)) @@ -408,13 +420,7 @@ static int pidns_install(struct nsset *nsset, struct ns_common *ns) * this maintains the property that processes and their * children can not escape their current pid namespace. */ - if (new->level < active->level) - return -EINVAL; - - ancestor = new; - while (ancestor->level > active->level) - ancestor = ancestor->parent; - if (ancestor != active) + if (!pidns_is_ancestor(new, active)) return -EINVAL;
put_pid_ns(nsproxy->pid_ns_for_children);
Since the introduction of pid namespaces, their interaction with procfs has been entirely implicit in ways that require a lot of dancing around by programs that need to construct sandboxes with different PID namespaces.
Being able to explicitly specify the pid namespace to use when constructing a procfs super block will allow programs to no longer need to fork off a process which does then does unshare(2) / setns(2) and forks again in order to construct a procfs in a pidns.
So, provide a "pidns" mount option which allows such users to just explicitly state which pid namespace they want that procfs instance to use. This interface can be used with fsconfig(2) either with a file descriptor or a path:
fsconfig(procfd, FSCONFIG_SET_FD, "pidns", NULL, nsfd); fsconfig(procfd, FSCONFIG_SET_STRING, "pidns", "/proc/self/ns/pid", 0);
or with classic mount(2) / mount(8):
// mount -t proc -o pidns=/proc/self/ns/pid proc /tmp/proc mount("proc", "/tmp/proc", "proc", MS_..., "pidns=/proc/self/ns/pid");
As this new API is effectively shorthand for setns(2) followed by mount(2), the permission model for this mirrors pidns_install() to avoid opening up new attack surfaces by loosening the existing permission model.
In order to avoid having to RCU-protect all users of proc_pid_ns() (to avoid UAFs), attempting to reconfigure an existing procfs instance's pid namespace will error out with -EBUSY. Creating new procfs instances is quite cheap, so this should not be an impediment to most users, and lets us avoid a lot of churn in fs/proc/* for a feature that it seems unlikely userspace would use.
Signed-off-by: Aleksa Sarai cyphar@cyphar.com --- Documentation/filesystems/proc.rst | 8 ++++ fs/proc/root.c | 98 +++++++++++++++++++++++++++++++++++--- 2 files changed, 100 insertions(+), 6 deletions(-)
diff --git a/Documentation/filesystems/proc.rst b/Documentation/filesystems/proc.rst index 5236cb52e357..5a157dadea0b 100644 --- a/Documentation/filesystems/proc.rst +++ b/Documentation/filesystems/proc.rst @@ -2360,6 +2360,7 @@ The following mount options are supported: hidepid= Set /proc/<pid>/ access mode. gid= Set the group authorized to learn processes information. subset= Show only the specified subset of procfs. + pidns= Specify a the namespace used by this procfs. ========= ========================================================
hidepid=off or hidepid=0 means classic mode - everybody may access all @@ -2392,6 +2393,13 @@ information about processes information, just add identd to this group. subset=pid hides all top level files and directories in the procfs that are not related to tasks.
+pidns= specifies a pid namespace (either as a string path to something like +`/proc/$pid/ns/pid`, or a file descriptor when using `FSCONFIG_SET_FD`) that +will be used by the procfs instance when translating pids. By default, procfs +will use the calling process's active pid namespace. Note that the pid +namespace of an existing procfs instance cannot be modified (attempting to do +so will give an `-EBUSY` error). + Chapter 5: Filesystem behavior ==============================
diff --git a/fs/proc/root.c b/fs/proc/root.c index ed86ac710384..fd1f1c8a939a 100644 --- a/fs/proc/root.c +++ b/fs/proc/root.c @@ -38,12 +38,14 @@ enum proc_param { Opt_gid, Opt_hidepid, Opt_subset, + Opt_pidns, };
static const struct fs_parameter_spec proc_fs_parameters[] = { - fsparam_u32("gid", Opt_gid), + fsparam_u32("gid", Opt_gid), fsparam_string("hidepid", Opt_hidepid), fsparam_string("subset", Opt_subset), + fsparam_file_or_string("pidns", Opt_pidns), {} };
@@ -109,11 +111,66 @@ static int proc_parse_subset_param(struct fs_context *fc, char *value) return 0; }
+#ifdef CONFIG_PID_NS +static int proc_parse_pidns_param(struct fs_context *fc, + struct fs_parameter *param, + struct fs_parse_result *result) +{ + struct proc_fs_context *ctx = fc->fs_private; + struct pid_namespace *target, *active = task_active_pid_ns(current); + struct ns_common *ns; + struct file *ns_filp __free(fput) = NULL; + + switch (param->type) { + case fs_value_is_file: + /* came through fsconfig, steal the file reference */ + ns_filp = no_free_ptr(param->file); + break; + case fs_value_is_string: + ns_filp = filp_open(param->string, O_RDONLY, 0); + break; + default: + WARN_ON_ONCE(true); + break; + } + if (!ns_filp) + ns_filp = ERR_PTR(-EBADF); + if (IS_ERR(ns_filp)) { + errorfc(fc, "could not get file from pidns argument"); + return PTR_ERR(ns_filp); + } + + if (!proc_ns_file(ns_filp)) + return invalfc(fc, "pidns argument is not an nsfs file"); + ns = get_proc_ns(file_inode(ns_filp)); + if (ns->ops->type != CLONE_NEWPID) + return invalfc(fc, "pidns argument is not a pidns file"); + target = container_of(ns, struct pid_namespace, ns); + + /* + * pidns= is shorthand for joining the pidns to get a fsopen fd, so the + * permission model should be the same as pidns_install(). + */ + if (!ns_capable(target->user_ns, CAP_SYS_ADMIN)) { + errorfc(fc, "insufficient permissions to set pidns"); + return -EPERM; + } + if (!pidns_is_ancestor(target, active)) + return invalfc(fc, "cannot set pidns to non-descendant pidns"); + + put_pid_ns(ctx->pid_ns); + ctx->pid_ns = get_pid_ns(target); + put_user_ns(fc->user_ns); + fc->user_ns = get_user_ns(ctx->pid_ns->user_ns); + return 0; +} +#endif /* CONFIG_PID_NS */ + static int proc_parse_param(struct fs_context *fc, struct fs_parameter *param) { struct proc_fs_context *ctx = fc->fs_private; struct fs_parse_result result; - int opt; + int opt, err;
opt = fs_parse(fc, proc_fs_parameters, param, &result); if (opt < 0) @@ -125,14 +182,38 @@ static int proc_parse_param(struct fs_context *fc, struct fs_parameter *param) break;
case Opt_hidepid: - if (proc_parse_hidepid_param(fc, param)) - return -EINVAL; + err = proc_parse_hidepid_param(fc, param); + if (err) + return err; break;
case Opt_subset: - if (proc_parse_subset_param(fc, param->string) < 0) - return -EINVAL; + err = proc_parse_subset_param(fc, param->string); + if (err) + return err; + break; + + case Opt_pidns: +#ifdef CONFIG_PID_NS + /* + * We would have to RCU-protect every proc_pid_ns() or + * proc_sb_info() access if we allowed this to be reconfigured + * for an existing procfs instance. Luckily, procfs instances + * are cheap to create, and mount-beneath would let you + * atomically replace an instance even with overmounts. + */ + if (fc->purpose == FS_CONTEXT_FOR_RECONFIGURE) { + errorfc(fc, "cannot reconfigure pidns for existing procfs"); + return -EBUSY; + } + err = proc_parse_pidns_param(fc, param, &result); + if (err) + return err; break; +#else + errorfc(fc, "pidns mount flag not supported on this system"); + return -EOPNOTSUPP; +#endif
default: return -EINVAL; @@ -154,6 +235,11 @@ static void proc_apply_options(struct proc_fs_info *fs_info, fs_info->hide_pid = ctx->hidepid; if (ctx->mask & (1 << Opt_subset)) fs_info->pidonly = ctx->pidonly; + if (ctx->mask & (1 << Opt_pidns) && + !WARN_ON_ONCE(fc->purpose == FS_CONTEXT_FOR_RECONFIGURE)) { + put_pid_ns(fs_info->pid_ns); + fs_info->pid_ns = get_pid_ns(ctx->pid_ns); + } }
static int proc_fill_super(struct super_block *s, struct fs_context *fc)
On 2025-08-05, Aleksa Sarai cyphar@cyphar.com wrote:
Since the introduction of pid namespaces, their interaction with procfs has been entirely implicit in ways that require a lot of dancing around by programs that need to construct sandboxes with different PID namespaces.
Being able to explicitly specify the pid namespace to use when constructing a procfs super block will allow programs to no longer need to fork off a process which does then does unshare(2) / setns(2) and forks again in order to construct a procfs in a pidns.
So, provide a "pidns" mount option which allows such users to just explicitly state which pid namespace they want that procfs instance to use. This interface can be used with fsconfig(2) either with a file descriptor or a path:
fsconfig(procfd, FSCONFIG_SET_FD, "pidns", NULL, nsfd); fsconfig(procfd, FSCONFIG_SET_STRING, "pidns", "/proc/self/ns/pid", 0);
or with classic mount(2) / mount(8):
// mount -t proc -o pidns=/proc/self/ns/pid proc /tmp/proc mount("proc", "/tmp/proc", "proc", MS_..., "pidns=/proc/self/ns/pid");
As this new API is effectively shorthand for setns(2) followed by mount(2), the permission model for this mirrors pidns_install() to avoid opening up new attack surfaces by loosening the existing permission model.
In order to avoid having to RCU-protect all users of proc_pid_ns() (to avoid UAFs), attempting to reconfigure an existing procfs instance's pid namespace will error out with -EBUSY. Creating new procfs instances is quite cheap, so this should not be an impediment to most users, and lets us avoid a lot of churn in fs/proc/* for a feature that it seems unlikely userspace would use.
Signed-off-by: Aleksa Sarai cyphar@cyphar.com
Documentation/filesystems/proc.rst | 8 ++++ fs/proc/root.c | 98 +++++++++++++++++++++++++++++++++++--- 2 files changed, 100 insertions(+), 6 deletions(-)
diff --git a/Documentation/filesystems/proc.rst b/Documentation/filesystems/proc.rst index 5236cb52e357..5a157dadea0b 100644 --- a/Documentation/filesystems/proc.rst +++ b/Documentation/filesystems/proc.rst @@ -2360,6 +2360,7 @@ The following mount options are supported: hidepid= Set /proc/<pid>/ access mode. gid= Set the group authorized to learn processes information. subset= Show only the specified subset of procfs.
- pidns= Specify a the namespace used by this procfs. ========= ========================================================
hidepid=off or hidepid=0 means classic mode - everybody may access all @@ -2392,6 +2393,13 @@ information about processes information, just add identd to this group. subset=pid hides all top level files and directories in the procfs that are not related to tasks. +pidns= specifies a pid namespace (either as a string path to something like +`/proc/$pid/ns/pid`, or a file descriptor when using `FSCONFIG_SET_FD`) that +will be used by the procfs instance when translating pids. By default, procfs +will use the calling process's active pid namespace. Note that the pid +namespace of an existing procfs instance cannot be modified (attempting to do +so will give an `-EBUSY` error).
Chapter 5: Filesystem behavior
diff --git a/fs/proc/root.c b/fs/proc/root.c index ed86ac710384..fd1f1c8a939a 100644 --- a/fs/proc/root.c +++ b/fs/proc/root.c @@ -38,12 +38,14 @@ enum proc_param { Opt_gid, Opt_hidepid, Opt_subset,
- Opt_pidns,
}; static const struct fs_parameter_spec proc_fs_parameters[] = {
- fsparam_u32("gid", Opt_gid),
- fsparam_u32("gid", Opt_gid), fsparam_string("hidepid", Opt_hidepid), fsparam_string("subset", Opt_subset),
- fsparam_file_or_string("pidns", Opt_pidns), {}
}; @@ -109,11 +111,66 @@ static int proc_parse_subset_param(struct fs_context *fc, char *value) return 0; } +#ifdef CONFIG_PID_NS +static int proc_parse_pidns_param(struct fs_context *fc,
struct fs_parameter *param,struct fs_parse_result *result)+{
- struct proc_fs_context *ctx = fc->fs_private;
- struct pid_namespace *target, *active = task_active_pid_ns(current);
- struct ns_common *ns;
- struct file *ns_filp __free(fput) = NULL;
- switch (param->type) {
- case fs_value_is_file:
/* came through fsconfig, steal the file reference */ns_filp = no_free_ptr(param->file);break;- case fs_value_is_string:
ns_filp = filp_open(param->string, O_RDONLY, 0);break;
I just realised that we probably also want to support FSCONFIG_SET_PATH here, but fsparam_file_or_string() doesn't handle that at the moment. I think we probably want to have fsparam_file_or_path() which would act like:
1. A path with FSCONFIG_SET_STRING and FSCONFIG_SET_PATH. 2. A file with FSCONFIG_SET_FD.
These are the semantics I would already expect from these kinds of flags, but at the moment FSCONFIG_SET_PATH is entirely disallowed.
@Amir:
I wonder if overlayfs (the only other user of fsparam_file_or_string()) would also prefer having these semantics? We could just migrate fsparam_file_or_string() to fsparam_file_or_path() everwhere, since I'm pretty sure these are the semantics userspace expects anyway.
- default:
WARN_ON_ONCE(true);break;- }
- if (!ns_filp)
ns_filp = ERR_PTR(-EBADF);- if (IS_ERR(ns_filp)) {
errorfc(fc, "could not get file from pidns argument");return PTR_ERR(ns_filp);- }
- if (!proc_ns_file(ns_filp))
return invalfc(fc, "pidns argument is not an nsfs file");- ns = get_proc_ns(file_inode(ns_filp));
- if (ns->ops->type != CLONE_NEWPID)
return invalfc(fc, "pidns argument is not a pidns file");- target = container_of(ns, struct pid_namespace, ns);
- /*
* pidns= is shorthand for joining the pidns to get a fsopen fd, so the* permission model should be the same as pidns_install().*/- if (!ns_capable(target->user_ns, CAP_SYS_ADMIN)) {
errorfc(fc, "insufficient permissions to set pidns");return -EPERM;- }
- if (!pidns_is_ancestor(target, active))
return invalfc(fc, "cannot set pidns to non-descendant pidns");- put_pid_ns(ctx->pid_ns);
- ctx->pid_ns = get_pid_ns(target);
- put_user_ns(fc->user_ns);
- fc->user_ns = get_user_ns(ctx->pid_ns->user_ns);
- return 0;
+} +#endif /* CONFIG_PID_NS */
static int proc_parse_param(struct fs_context *fc, struct fs_parameter *param) { struct proc_fs_context *ctx = fc->fs_private; struct fs_parse_result result;
- int opt;
- int opt, err;
opt = fs_parse(fc, proc_fs_parameters, param, &result); if (opt < 0) @@ -125,14 +182,38 @@ static int proc_parse_param(struct fs_context *fc, struct fs_parameter *param) break; case Opt_hidepid:
if (proc_parse_hidepid_param(fc, param))return -EINVAL;
err = proc_parse_hidepid_param(fc, param);if (err)return err;case Opt_subset:
if (proc_parse_subset_param(fc, param->string) < 0)return -EINVAL;
err = proc_parse_subset_param(fc, param->string);if (err)return err;break;- case Opt_pidns:
+#ifdef CONFIG_PID_NS
/** We would have to RCU-protect every proc_pid_ns() or* proc_sb_info() access if we allowed this to be reconfigured* for an existing procfs instance. Luckily, procfs instances* are cheap to create, and mount-beneath would let you* atomically replace an instance even with overmounts.*/if (fc->purpose == FS_CONTEXT_FOR_RECONFIGURE) {errorfc(fc, "cannot reconfigure pidns for existing procfs");return -EBUSY;}err = proc_parse_pidns_param(fc, param, &result);if (err)return err;+#else
errorfc(fc, "pidns mount flag not supported on this system");return -EOPNOTSUPP;+#endif default: return -EINVAL; @@ -154,6 +235,11 @@ static void proc_apply_options(struct proc_fs_info *fs_info, fs_info->hide_pid = ctx->hidepid; if (ctx->mask & (1 << Opt_subset)) fs_info->pidonly = ctx->pidonly;
- if (ctx->mask & (1 << Opt_pidns) &&
!WARN_ON_ONCE(fc->purpose == FS_CONTEXT_FOR_RECONFIGURE)) {put_pid_ns(fs_info->pid_ns);fs_info->pid_ns = get_pid_ns(ctx->pid_ns);- }
} static int proc_fill_super(struct super_block *s, struct fs_context *fc)
-- 2.50.1
I just realised that we probably also want to support FSCONFIG_SET_PATH
I just checked kernel code. Indeed nobody uses FSCONFIG_SET_PATH. Moreover, fsparam_path macro is present since 5.1. And for all this time nobody used it. So, let's just remove FSCONFIG_SET_PATH. Nobody used it, so this will not break anything.
If you okay with that, I can submit patch, removing it.
-- Askar Safin
On 2025-08-06, Askar Safin safinaskar@zohomail.com wrote:
I just realised that we probably also want to support FSCONFIG_SET_PATH
I just checked kernel code. Indeed nobody uses FSCONFIG_SET_PATH. Moreover, fsparam_path macro is present since 5.1. And for all this time nobody used it. So, let's just remove FSCONFIG_SET_PATH. Nobody used it, so this will not break anything.
If you okay with that, I can submit patch, removing it.
I would prefer you didn't -- "*at()" semantics are very useful to a lot of programs (*especially* AT_EMPTY_PATH). I would like the pidns= stuff to support it, and probably also overlayfs...
I suspect the primary issue is that when migrating to the new mount API, filesystem devs just went with the easiest thing to use (FSCONFIG_SET_STRING) even though FSCONFIG_SET_PATH would be better. I suspect the lack of documentation around fsconfig(2) played a part too.
My impression is that interest in the minutia about fsconfig(2) is quite low on the list of priorities for most filesystem devs, and so the neat aspects of fsconfig(2) haven't been fully utilised. (In LPC last year, we struggled to come to an agreement on how filesystems should use the read(2)-based error interface.)
We can very easily move fsparam_string() or fsparam_file_or_string() parameters to fsparam_path() and a future fsparam_file_or_path(). I would much prefer that as a user.
On 2025-08-07, Aleksa Sarai cyphar@cyphar.com wrote:
On 2025-08-06, Askar Safin safinaskar@zohomail.com wrote:
I just realised that we probably also want to support FSCONFIG_SET_PATH
I just checked kernel code. Indeed nobody uses FSCONFIG_SET_PATH. Moreover, fsparam_path macro is present since 5.1. And for all this time nobody used it. So, let's just remove FSCONFIG_SET_PATH. Nobody used it, so this will not break anything.
If you okay with that, I can submit patch, removing it.
I would prefer you didn't -- "*at()" semantics are very useful to a lot of programs (*especially* AT_EMPTY_PATH). I would like the pidns= stuff to support it, and probably also overlayfs...
I suspect the primary issue is that when migrating to the new mount API, filesystem devs just went with the easiest thing to use (FSCONFIG_SET_STRING) even though FSCONFIG_SET_PATH would be better. I suspect the lack of documentation around fsconfig(2) played a part too.
My impression is that interest in the minutia about fsconfig(2) is quite low on the list of priorities for most filesystem devs, and so the neat aspects of fsconfig(2) haven't been fully utilised. (In LPC last year, we struggled to come to an agreement on how filesystems should use the read(2)-based error interface.)
We can very easily move fsparam_string() or fsparam_file_or_string() parameters to fsparam_path() and a future fsparam_file_or_path(). I would much prefer that as a user.
Actually, fsparam_bdev() accepts FSCONFIG_SET_PATH in a very roundabout way (and the checker doesn't verify anything...?). So there is at least one user (ext4's "journal_path"), it's just not well-documented (which I'm trying to fix ;]).
My plan is to update fs_lookup_param() to be more useful for the (fairly common) use-case of wanting to support paths and file descriptors, and going through to clean up some of these unused fsparam_* helpers (or fsparam_* helpers being abused to implement stuff that the fs_parser core already supports).
At the very least, overlayfs, ext4, and this procfs patchset can make use of it.
On Thu, Aug 07, 2025 at 05:17:56PM +1000, Aleksa Sarai wrote:
On 2025-08-07, Aleksa Sarai cyphar@cyphar.com wrote:
On 2025-08-06, Askar Safin safinaskar@zohomail.com wrote:
I just realised that we probably also want to support FSCONFIG_SET_PATH
I just checked kernel code. Indeed nobody uses FSCONFIG_SET_PATH. Moreover, fsparam_path macro is present since 5.1. And for all this time nobody used it. So, let's just remove FSCONFIG_SET_PATH. Nobody used it, so this will not break anything.
If you okay with that, I can submit patch, removing it.
I would prefer you didn't -- "*at()" semantics are very useful to a lot of programs (*especially* AT_EMPTY_PATH). I would like the pidns= stuff to support it, and probably also overlayfs...
I suspect the primary issue is that when migrating to the new mount API, filesystem devs just went with the easiest thing to use (FSCONFIG_SET_STRING) even though FSCONFIG_SET_PATH would be better. I suspect the lack of documentation around fsconfig(2) played a part too.
My impression is that interest in the minutia about fsconfig(2) is quite low on the list of priorities for most filesystem devs, and so the neat aspects of fsconfig(2) haven't been fully utilised. (In LPC last year, we struggled to come to an agreement on how filesystems should use the read(2)-based error interface.)
We can very easily move fsparam_string() or fsparam_file_or_string() parameters to fsparam_path() and a future fsparam_file_or_path(). I would much prefer that as a user.
Actually, fsparam_bdev() accepts FSCONFIG_SET_PATH in a very roundabout way (and the checker doesn't verify anything...?). So there is at least one user (ext4's "journal_path"), it's just not well-documented (which I'm trying to fix ;]).
My plan is to update fs_lookup_param() to be more useful for the (fairly common) use-case of wanting to support paths and file descriptors, and going through to clean up some of these unused fsparam_* helpers (or fsparam_* helpers being abused to implement stuff that the fs_parser core already supports).
At the very least, overlayfs, ext4, and this procfs patchset can make use of it.
I've never bothered with actually iplementing FSCONFIG_SET_PATH semantics because I think it's really weird to allow *at semantics when setting filesystem parameters. I always thought it's better to force userspace to provide a file descriptor for the final destination instead of doing some arcane lookup variant for mount configuration. But I'm happy to be convinced of its usefulness...
On 2025-08-08, Christian Brauner brauner@kernel.org wrote:
On Thu, Aug 07, 2025 at 05:17:56PM +1000, Aleksa Sarai wrote:
On 2025-08-07, Aleksa Sarai cyphar@cyphar.com wrote:
On 2025-08-06, Askar Safin safinaskar@zohomail.com wrote:
I just realised that we probably also want to support FSCONFIG_SET_PATH
I just checked kernel code. Indeed nobody uses FSCONFIG_SET_PATH. Moreover, fsparam_path macro is present since 5.1. And for all this time nobody used it. So, let's just remove FSCONFIG_SET_PATH. Nobody used it, so this will not break anything.
If you okay with that, I can submit patch, removing it.
I would prefer you didn't -- "*at()" semantics are very useful to a lot of programs (*especially* AT_EMPTY_PATH). I would like the pidns= stuff to support it, and probably also overlayfs...
I suspect the primary issue is that when migrating to the new mount API, filesystem devs just went with the easiest thing to use (FSCONFIG_SET_STRING) even though FSCONFIG_SET_PATH would be better. I suspect the lack of documentation around fsconfig(2) played a part too.
My impression is that interest in the minutia about fsconfig(2) is quite low on the list of priorities for most filesystem devs, and so the neat aspects of fsconfig(2) haven't been fully utilised. (In LPC last year, we struggled to come to an agreement on how filesystems should use the read(2)-based error interface.)
We can very easily move fsparam_string() or fsparam_file_or_string() parameters to fsparam_path() and a future fsparam_file_or_path(). I would much prefer that as a user.
Actually, fsparam_bdev() accepts FSCONFIG_SET_PATH in a very roundabout way (and the checker doesn't verify anything...?). So there is at least one user (ext4's "journal_path"), it's just not well-documented (which I'm trying to fix ;]).
My plan is to update fs_lookup_param() to be more useful for the (fairly common) use-case of wanting to support paths and file descriptors, and going through to clean up some of these unused fsparam_* helpers (or fsparam_* helpers being abused to implement stuff that the fs_parser core already supports).
At the very least, overlayfs, ext4, and this procfs patchset can make use of it.
I've never bothered with actually iplementing FSCONFIG_SET_PATH semantics because I think it's really weird to allow *at semantics when setting filesystem parameters. I always thought it's better to force userspace to provide a file descriptor for the final destination instead of doing some arcane lookup variant for mount configuration. But I'm happy to be convinced of its usefulness...
I do think it's useful, and here's my thought process...
Most filesystems have to take string path parameters in order to support mount(2) and work with mount(8). Yes, fsparam_fd() will accept FSCONFIG_SET_STRING by parsing it as a decimal string, but there are only two users of fsparam_fd() and honestly I'm not convinced this is a particularly sane API for anything other than strict backcompat reasons (the API only makes sense as a file descriptor and you want mount(8) to be able to use it).
So you end up with most parameters supporting paths set using FSCONFIG_SET_STRING anyway, meaning in-kernel lookups can't be taken off the table. And if we accept paths for lookup, then (for the same reason we have *at(2) syscalls) it is preferable to allow specifying dirfds. So FSCONFIG_SET_PATH should also be supported.
And as there is no infrastructure to block FSCONFIG_SET_PATH_EMPTY arguments (yes, you can do it manually, but the *only* user of fs_lookup_param() doesn't), then anything that accepts FSCONFIG_SET_PATH currently also accepts FSCONFIG_SET_PATH_EMPTY which is "morally equivalent" to FSCONFIG_SET_FD. So unless you block FSCONFIG_SET_PATH_EMPTY then FSCONFIG_SET_FD should probably also be supported (there is the re-opening distinction, of course, but that is not relevant if you use filename_lookup() -- which is what filesystems will do in practice).
So my impression is that most users (if they had an fsconfig(2) man page to read...) would expect parameters that accept paths to either:
* Work with FSCONFIG_SET_STRING and FSCONFIG_SET_PATH only; or * Work with FSCONFIG_SET_STRING, FSCONFIG_SET_PATH, FSCONFIG_SET_PATH_EMPTY, and FSCONFIG_SET_FD.
Currently, none of our parameters work that way.
* ext4's journal_path takes FSCONFIG_SET_STRING, FSCONFIG_SET_PATH, and FSCONFIG_SET_PATH_EMPTY. * overlayfs takes FSCONFIG_SET_FD and FSCONFIG_SET_STRING.
I only fully realised how inconsistent this is while working on the fsconfig(2) man pages -- at the moment I have a very long paragraph explaining that there is this distinction in-kernel, but this really doesn't seem intentional to me. I would be very confused as a user that FSCONFIG_SET_PATH is useless for most filesystem *path* parameters, even though the filesystem accepts them as FSCONFIG_SET_STRING.
As for practical uses, it would be nice to not have to open 500 files in order to create a 500-layer overlayfs.
Hi,
On 8/4/25 10:45 PM, Aleksa Sarai wrote:
Since the introduction of pid namespaces, their interaction with procfs has been entirely implicit in ways that require a lot of dancing around by programs that need to construct sandboxes with different PID namespaces.
Being able to explicitly specify the pid namespace to use when constructing a procfs super block will allow programs to no longer need to fork off a process which does then does unshare(2) / setns(2) and forks again in order to construct a procfs in a pidns.
So, provide a "pidns" mount option which allows such users to just explicitly state which pid namespace they want that procfs instance to use. This interface can be used with fsconfig(2) either with a file descriptor or a path:
fsconfig(procfd, FSCONFIG_SET_FD, "pidns", NULL, nsfd); fsconfig(procfd, FSCONFIG_SET_STRING, "pidns", "/proc/self/ns/pid", 0);
or with classic mount(2) / mount(8):
// mount -t proc -o pidns=/proc/self/ns/pid proc /tmp/proc mount("proc", "/tmp/proc", "proc", MS_..., "pidns=/proc/self/ns/pid");
As this new API is effectively shorthand for setns(2) followed by mount(2), the permission model for this mirrors pidns_install() to avoid opening up new attack surfaces by loosening the existing permission model.
In order to avoid having to RCU-protect all users of proc_pid_ns() (to avoid UAFs), attempting to reconfigure an existing procfs instance's pid namespace will error out with -EBUSY. Creating new procfs instances is quite cheap, so this should not be an impediment to most users, and lets us avoid a lot of churn in fs/proc/* for a feature that it seems unlikely userspace would use.
Signed-off-by: Aleksa Sarai cyphar@cyphar.com
Documentation/filesystems/proc.rst | 8 ++++ fs/proc/root.c | 98 +++++++++++++++++++++++++++++++++++--- 2 files changed, 100 insertions(+), 6 deletions(-)
diff --git a/Documentation/filesystems/proc.rst b/Documentation/filesystems/proc.rst index 5236cb52e357..5a157dadea0b 100644 --- a/Documentation/filesystems/proc.rst +++ b/Documentation/filesystems/proc.rst @@ -2360,6 +2360,7 @@ The following mount options are supported: hidepid= Set /proc/<pid>/ access mode. gid= Set the group authorized to learn processes information. subset= Show only the specified subset of procfs.
- pidns= Specify a the namespace used by this procfs.
drop ^^ a
========= ======================================================== hidepid=off or hidepid=0 means classic mode - everybody may access all @@ -2392,6 +2393,13 @@ information about processes information, just add identd to this group. subset=pid hides all top level files and directories in the procfs that are not related to tasks. +pidns= specifies a pid namespace (either as a string path to something like +`/proc/$pid/ns/pid`, or a file descriptor when using `FSCONFIG_SET_FD`) that +will be used by the procfs instance when translating pids. By default, procfs +will use the calling process's active pid namespace. Note that the pid +namespace of an existing procfs instance cannot be modified (attempting to do +so will give an `-EBUSY` error).
Chapter 5: Filesystem behavior
/proc has historically had very opaque semantics about PID namespaces, which is a little unfortunate for container runtimes and other programs that deal with switching namespaces very often. One common issue is that of converting between PIDs in the process's namespace and PIDs in the namespace of /proc.
In principle, it is possible to do this today by opening a pidfd with pidfd_open(2) and then looking at /proc/self/fdinfo/$n (which will contain a PID value translated to the pid namespace associated with that procfs superblock). However, allocating a new file for each PID to be converted is less than ideal for programs that may need to scan procfs, and it is generally useful for userspace to be able to finally get this information from procfs.
So, add a new API to get the pid namespace of a procfs instance, in the form of an ioctl(2) you can call on the root directory of said procfs. The returned file descriptor will have O_CLOEXEC set. This acts as a sister feature to the new "pidns" mount option, finally allowing userspace full control of the pid namespaces associated with procfs instances.
The permission model for this is a bit looser than that of the "pidns" mount option (and also setns(2)) because /proc/1/ns/pid provides the same information, so as long as you have access to that magic-link (or something equivalently reasonable such as being in an ancestor pid namespace) it makes sense to allow userspace to grab a handle. Ideally we would check for ptrace-read access against all processes in the pidns (which is very likely to be true for at least one process, as SUID_DUMP_DISABLE is cleared on exec(2) and is rarely set by most programs), but this would obviously not scale.
setns(2) will still have their own permission checks, so being able to open a pidns handle doesn't really provide too many other capabilities.
Signed-off-by: Aleksa Sarai cyphar@cyphar.com --- Documentation/filesystems/proc.rst | 4 +++ fs/proc/root.c | 68 ++++++++++++++++++++++++++++++++++++-- include/uapi/linux/fs.h | 4 +++ 3 files changed, 74 insertions(+), 2 deletions(-)
diff --git a/Documentation/filesystems/proc.rst b/Documentation/filesystems/proc.rst index 5a157dadea0b..840f820fb467 100644 --- a/Documentation/filesystems/proc.rst +++ b/Documentation/filesystems/proc.rst @@ -2400,6 +2400,10 @@ will use the calling process's active pid namespace. Note that the pid namespace of an existing procfs instance cannot be modified (attempting to do so will give an `-EBUSY` error).
+Processes can check which pid namespace is used by a procfs instance by using +the `PROCFS_GET_PID_NAMESPACE` ioctl() on the root directory of the procfs +instance. + Chapter 5: Filesystem behavior ==============================
diff --git a/fs/proc/root.c b/fs/proc/root.c index fd1f1c8a939a..ac9b115fad7b 100644 --- a/fs/proc/root.c +++ b/fs/proc/root.c @@ -23,8 +23,10 @@ #include <linux/cred.h> #include <linux/magic.h> #include <linux/slab.h> +#include <linux/ptrace.h>
#include "internal.h" +#include "../internal.h"
struct proc_fs_context { struct pid_namespace *pid_ns; @@ -426,15 +428,77 @@ static int proc_root_readdir(struct file *file, struct dir_context *ctx) return proc_pid_readdir(file, ctx); }
+static long int proc_root_ioctl(struct file *filp, unsigned int cmd, unsigned long arg) +{ + switch (cmd) { + case PROCFS_GET_PID_NAMESPACE: { +#ifdef CONFIG_PID_NS + struct pid_namespace *active = task_active_pid_ns(current); + struct pid_namespace *ns = proc_pid_ns(file_inode(filp)->i_sb); + bool can_access_pidns = false; + + /* + * Having a handle to a pidns is not sufficient to do anything + * particularly harmful, as setns(2) has its own separate + * privilege checks. So, we can loosen the privilege + * requirements here a little to make this more ergonomic. + * + * If we are in an ancestor pidns of the pidns, then we can + * already address any process in the pidns. From a setns(2) + * privileges perspective, we can create a pidfd which setns(2) + * would also accept (pending any privilege checks). + * + * If we are not in an ancestor pidns, because this operation + * is being done on the root of the /proc instance, the caller + * can try to access /proc/1/ns/pid which is equivalent to this + * ioctl and so we should copy the PTRACE_MODE_READ_FSCREDS + * permission model use by proc_ns_get_link(). Ideally we would + * check for ptrace-read access against all processes in the + * pidns (which is very likely to be true for at least one + * process, as SUID_DUMP_DISABLE is cleared on exec(2) and is + * rarely set by most programs), but this would obviously not + * scale. + * + * If there is no root process, then there is no real downside + * to unprivileged users to open a handle to it. + */ + can_access_pidns = pidns_is_ancestor(ns, active); + if (!can_access_pidns) { + bool cannot_ptrace_pid1 = false; + + read_lock(&tasklist_lock); + if (ns->child_reaper) + cannot_ptrace_pid1 = ptrace_may_access(ns->child_reaper, + PTRACE_MODE_READ_FSCREDS); + read_unlock(&tasklist_lock); + can_access_pidns = !cannot_ptrace_pid1; + } + if (!can_access_pidns) + return -EPERM; + + /* open_namespace() unconditionally consumes the reference. */ + get_pid_ns(ns); + return open_namespace(to_ns_common(ns)); +#else + return -EOPNOTSUPP; +#endif + } + default: + return -ENOIOCTLCMD; + } +} + /* * The root /proc directory is special, as it has the * <pid> directories. Thus we don't use the generic * directory handling functions for that.. */ static const struct file_operations proc_root_operations = { - .read = generic_read_dir, - .iterate_shared = proc_root_readdir, + .read = generic_read_dir, + .iterate_shared = proc_root_readdir, .llseek = generic_file_llseek, + .unlocked_ioctl = proc_root_ioctl, + .compat_ioctl = compat_ptr_ioctl, };
/* diff --git a/include/uapi/linux/fs.h b/include/uapi/linux/fs.h index 0bd678a4a10e..68e65e6d7d6b 100644 --- a/include/uapi/linux/fs.h +++ b/include/uapi/linux/fs.h @@ -435,8 +435,12 @@ typedef int __bitwise __kernel_rwf_t; RWF_APPEND | RWF_NOAPPEND | RWF_ATOMIC |\ RWF_DONTCACHE)
+/* This matches XSDFEC_MAGIC, so we need to allocate subvalues carefully. */ #define PROCFS_IOCTL_MAGIC 'f'
+/* procfs root ioctls */ +#define PROCFS_GET_PID_NAMESPACE _IO(PROCFS_IOCTL_MAGIC, 32) + /* Pagemap ioctl */ #define PAGEMAP_SCAN _IOWR(PROCFS_IOCTL_MAGIC, 16, struct pm_scan_arg)
On 8/4/25 10:45 PM, Aleksa Sarai wrote:
/proc has historically had very opaque semantics about PID namespaces, which is a little unfortunate for container runtimes and other programs that deal with switching namespaces very often. One common issue is that of converting between PIDs in the process's namespace and PIDs in the namespace of /proc.
In principle, it is possible to do this today by opening a pidfd with pidfd_open(2) and then looking at /proc/self/fdinfo/$n (which will contain a PID value translated to the pid namespace associated with that procfs superblock). However, allocating a new file for each PID to be converted is less than ideal for programs that may need to scan procfs, and it is generally useful for userspace to be able to finally get this information from procfs.
So, add a new API to get the pid namespace of a procfs instance, in the form of an ioctl(2) you can call on the root directory of said procfs. The returned file descriptor will have O_CLOEXEC set. This acts as a sister feature to the new "pidns" mount option, finally allowing userspace full control of the pid namespaces associated with procfs instances.
The permission model for this is a bit looser than that of the "pidns" mount option (and also setns(2)) because /proc/1/ns/pid provides the same information, so as long as you have access to that magic-link (or something equivalently reasonable such as being in an ancestor pid namespace) it makes sense to allow userspace to grab a handle. Ideally we would check for ptrace-read access against all processes in the pidns (which is very likely to be true for at least one process, as SUID_DUMP_DISABLE is cleared on exec(2) and is rarely set by most programs), but this would obviously not scale.
setns(2) will still have their own permission checks, so being able to open a pidns handle doesn't really provide too many other capabilities.
Signed-off-by: Aleksa Sarai cyphar@cyphar.com
Documentation/filesystems/proc.rst | 4 +++ fs/proc/root.c | 68 ++++++++++++++++++++++++++++++++++++-- include/uapi/linux/fs.h | 4 +++ 3 files changed, 74 insertions(+), 2 deletions(-)
diff --git a/include/uapi/linux/fs.h b/include/uapi/linux/fs.h index 0bd678a4a10e..68e65e6d7d6b 100644 --- a/include/uapi/linux/fs.h +++ b/include/uapi/linux/fs.h @@ -435,8 +435,12 @@ typedef int __bitwise __kernel_rwf_t; RWF_APPEND | RWF_NOAPPEND | RWF_ATOMIC |\ RWF_DONTCACHE) +/* This matches XSDFEC_MAGIC, so we need to allocate subvalues carefully. */ #define PROCFS_IOCTL_MAGIC 'f' +/* procfs root ioctls */ +#define PROCFS_GET_PID_NAMESPACE _IO(PROCFS_IOCTL_MAGIC, 32)
Since the _IO() nr here is 32, Documentation/userspace-api/ioctl/ioctl-number.rst should be updated like:
-'f' 00-0F linux/fs.h conflict! +'f' 00-1F linux/fs.h conflict!
(17 is already used for PROCFS_IOCTL_MAGIC somewhere else, so that probably should have update the Doc/rst file.)
/* Pagemap ioctl */ #define PAGEMAP_SCAN _IOWR(PROCFS_IOCTL_MAGIC, 16, struct pm_scan_arg)
Thanks.
On 2025-08-05, Randy Dunlap rdunlap@infradead.org wrote:
On 8/4/25 10:45 PM, Aleksa Sarai wrote:
/proc has historically had very opaque semantics about PID namespaces, which is a little unfortunate for container runtimes and other programs that deal with switching namespaces very often. One common issue is that of converting between PIDs in the process's namespace and PIDs in the namespace of /proc.
In principle, it is possible to do this today by opening a pidfd with pidfd_open(2) and then looking at /proc/self/fdinfo/$n (which will contain a PID value translated to the pid namespace associated with that procfs superblock). However, allocating a new file for each PID to be converted is less than ideal for programs that may need to scan procfs, and it is generally useful for userspace to be able to finally get this information from procfs.
So, add a new API to get the pid namespace of a procfs instance, in the form of an ioctl(2) you can call on the root directory of said procfs. The returned file descriptor will have O_CLOEXEC set. This acts as a sister feature to the new "pidns" mount option, finally allowing userspace full control of the pid namespaces associated with procfs instances.
The permission model for this is a bit looser than that of the "pidns" mount option (and also setns(2)) because /proc/1/ns/pid provides the same information, so as long as you have access to that magic-link (or something equivalently reasonable such as being in an ancestor pid namespace) it makes sense to allow userspace to grab a handle. Ideally we would check for ptrace-read access against all processes in the pidns (which is very likely to be true for at least one process, as SUID_DUMP_DISABLE is cleared on exec(2) and is rarely set by most programs), but this would obviously not scale.
setns(2) will still have their own permission checks, so being able to open a pidns handle doesn't really provide too many other capabilities.
Signed-off-by: Aleksa Sarai cyphar@cyphar.com
Documentation/filesystems/proc.rst | 4 +++ fs/proc/root.c | 68 ++++++++++++++++++++++++++++++++++++-- include/uapi/linux/fs.h | 4 +++ 3 files changed, 74 insertions(+), 2 deletions(-)
diff --git a/include/uapi/linux/fs.h b/include/uapi/linux/fs.h index 0bd678a4a10e..68e65e6d7d6b 100644 --- a/include/uapi/linux/fs.h +++ b/include/uapi/linux/fs.h @@ -435,8 +435,12 @@ typedef int __bitwise __kernel_rwf_t; RWF_APPEND | RWF_NOAPPEND | RWF_ATOMIC |\ RWF_DONTCACHE) +/* This matches XSDFEC_MAGIC, so we need to allocate subvalues carefully. */ #define PROCFS_IOCTL_MAGIC 'f' +/* procfs root ioctls */ +#define PROCFS_GET_PID_NAMESPACE _IO(PROCFS_IOCTL_MAGIC, 32)
Since the _IO() nr here is 32, Documentation/userspace-api/ioctl/ioctl-number.rst should be updated like:
-'f' 00-0F linux/fs.h conflict! +'f' 00-1F linux/fs.h conflict!
Should this be 00-20 (or 00-2F) instead?
Also, is there a better value to use for this new ioctl? I'm not quite sure what is the best practice to handle these kinds of conflicts...
(17 is already used for PROCFS_IOCTL_MAGIC somewhere else, so that probably should have update the Doc/rst file.)
/* Pagemap ioctl */ #define PAGEMAP_SCAN _IOWR(PROCFS_IOCTL_MAGIC, 16, struct pm_scan_arg)
Thanks.
~Randy
On 8/6/25 11:02 AM, Aleksa Sarai wrote:
On 2025-08-05, Randy Dunlap rdunlap@infradead.org wrote:
On 8/4/25 10:45 PM, Aleksa Sarai wrote:
/proc has historically had very opaque semantics about PID namespaces, which is a little unfortunate for container runtimes and other programs that deal with switching namespaces very often. One common issue is that of converting between PIDs in the process's namespace and PIDs in the namespace of /proc.
In principle, it is possible to do this today by opening a pidfd with pidfd_open(2) and then looking at /proc/self/fdinfo/$n (which will contain a PID value translated to the pid namespace associated with that procfs superblock). However, allocating a new file for each PID to be converted is less than ideal for programs that may need to scan procfs, and it is generally useful for userspace to be able to finally get this information from procfs.
So, add a new API to get the pid namespace of a procfs instance, in the form of an ioctl(2) you can call on the root directory of said procfs. The returned file descriptor will have O_CLOEXEC set. This acts as a sister feature to the new "pidns" mount option, finally allowing userspace full control of the pid namespaces associated with procfs instances.
The permission model for this is a bit looser than that of the "pidns" mount option (and also setns(2)) because /proc/1/ns/pid provides the same information, so as long as you have access to that magic-link (or something equivalently reasonable such as being in an ancestor pid namespace) it makes sense to allow userspace to grab a handle. Ideally we would check for ptrace-read access against all processes in the pidns (which is very likely to be true for at least one process, as SUID_DUMP_DISABLE is cleared on exec(2) and is rarely set by most programs), but this would obviously not scale.
setns(2) will still have their own permission checks, so being able to open a pidns handle doesn't really provide too many other capabilities.
Signed-off-by: Aleksa Sarai cyphar@cyphar.com
Documentation/filesystems/proc.rst | 4 +++ fs/proc/root.c | 68 ++++++++++++++++++++++++++++++++++++-- include/uapi/linux/fs.h | 4 +++ 3 files changed, 74 insertions(+), 2 deletions(-)
diff --git a/include/uapi/linux/fs.h b/include/uapi/linux/fs.h index 0bd678a4a10e..68e65e6d7d6b 100644 --- a/include/uapi/linux/fs.h +++ b/include/uapi/linux/fs.h @@ -435,8 +435,12 @@ typedef int __bitwise __kernel_rwf_t; RWF_APPEND | RWF_NOAPPEND | RWF_ATOMIC |\ RWF_DONTCACHE) +/* This matches XSDFEC_MAGIC, so we need to allocate subvalues carefully. */ #define PROCFS_IOCTL_MAGIC 'f' +/* procfs root ioctls */ +#define PROCFS_GET_PID_NAMESPACE _IO(PROCFS_IOCTL_MAGIC, 32)
Since the _IO() nr here is 32, Documentation/userspace-api/ioctl/ioctl-number.rst should be updated like:
-'f' 00-0F linux/fs.h conflict! +'f' 00-1F linux/fs.h conflict!
Should this be 00-20 (or 00-2F) instead?
Oops, yes, it should be one of those. Thanks.
Also, is there a better value to use for this new ioctl? I'm not quite sure what is the best practice to handle these kinds of conflicts...
I wouldn't worry about it. We have *many* conflicts. (unless Al or Christian are concerned)
(17 is already used for PROCFS_IOCTL_MAGIC somewhere else, so that probably should have update the Doc/rst file.)
/* Pagemap ioctl */ #define PAGEMAP_SCAN _IOWR(PROCFS_IOCTL_MAGIC, 16, struct pm_scan_arg)
On Wed, Aug 06, 2025 at 11:57:42AM -0700, Randy Dunlap wrote:
On 8/6/25 11:02 AM, Aleksa Sarai wrote:
On 2025-08-05, Randy Dunlap rdunlap@infradead.org wrote:
On 8/4/25 10:45 PM, Aleksa Sarai wrote:
/proc has historically had very opaque semantics about PID namespaces, which is a little unfortunate for container runtimes and other programs that deal with switching namespaces very often. One common issue is that of converting between PIDs in the process's namespace and PIDs in the namespace of /proc.
In principle, it is possible to do this today by opening a pidfd with pidfd_open(2) and then looking at /proc/self/fdinfo/$n (which will contain a PID value translated to the pid namespace associated with that procfs superblock). However, allocating a new file for each PID to be converted is less than ideal for programs that may need to scan procfs, and it is generally useful for userspace to be able to finally get this information from procfs.
So, add a new API to get the pid namespace of a procfs instance, in the form of an ioctl(2) you can call on the root directory of said procfs. The returned file descriptor will have O_CLOEXEC set. This acts as a sister feature to the new "pidns" mount option, finally allowing userspace full control of the pid namespaces associated with procfs instances.
The permission model for this is a bit looser than that of the "pidns" mount option (and also setns(2)) because /proc/1/ns/pid provides the same information, so as long as you have access to that magic-link (or something equivalently reasonable such as being in an ancestor pid namespace) it makes sense to allow userspace to grab a handle. Ideally we would check for ptrace-read access against all processes in the pidns (which is very likely to be true for at least one process, as SUID_DUMP_DISABLE is cleared on exec(2) and is rarely set by most programs), but this would obviously not scale.
setns(2) will still have their own permission checks, so being able to open a pidns handle doesn't really provide too many other capabilities.
Signed-off-by: Aleksa Sarai cyphar@cyphar.com
Documentation/filesystems/proc.rst | 4 +++ fs/proc/root.c | 68 ++++++++++++++++++++++++++++++++++++-- include/uapi/linux/fs.h | 4 +++ 3 files changed, 74 insertions(+), 2 deletions(-)
diff --git a/include/uapi/linux/fs.h b/include/uapi/linux/fs.h index 0bd678a4a10e..68e65e6d7d6b 100644 --- a/include/uapi/linux/fs.h +++ b/include/uapi/linux/fs.h @@ -435,8 +435,12 @@ typedef int __bitwise __kernel_rwf_t; RWF_APPEND | RWF_NOAPPEND | RWF_ATOMIC |\ RWF_DONTCACHE) +/* This matches XSDFEC_MAGIC, so we need to allocate subvalues carefully. */ #define PROCFS_IOCTL_MAGIC 'f' +/* procfs root ioctls */ +#define PROCFS_GET_PID_NAMESPACE _IO(PROCFS_IOCTL_MAGIC, 32)
Since the _IO() nr here is 32, Documentation/userspace-api/ioctl/ioctl-number.rst should be updated like:
-'f' 00-0F linux/fs.h conflict! +'f' 00-1F linux/fs.h conflict!
Should this be 00-20 (or 00-2F) instead?
Oops, yes, it should be one of those. Thanks.
Also, is there a better value to use for this new ioctl? I'm not quite sure what is the best practice to handle these kinds of conflicts...
I wouldn't worry about it. We have *many* conflicts. (unless Al or Christian are concerned)
We try to minimize conflicts but we unfortunately give no strong guarantees in any way. I always defer to Arnd in such matters as he's got a pretty good mental model of what is best to do for ioctls.
(17 is already used for PROCFS_IOCTL_MAGIC somewhere else, so that probably should have update the Doc/rst file.)
Signed-off-by: Aleksa Sarai cyphar@cyphar.com --- tools/testing/selftests/proc/.gitignore | 1 + tools/testing/selftests/proc/Makefile | 1 + tools/testing/selftests/proc/proc-pidns.c | 315 ++++++++++++++++++++++++++++++ 3 files changed, 317 insertions(+)
diff --git a/tools/testing/selftests/proc/.gitignore b/tools/testing/selftests/proc/.gitignore index 973968f45bba..2dced03e9e0e 100644 --- a/tools/testing/selftests/proc/.gitignore +++ b/tools/testing/selftests/proc/.gitignore @@ -17,6 +17,7 @@ /proc-tid0 /proc-uptime-001 /proc-uptime-002 +/proc-pidns /read /self /setns-dcache diff --git a/tools/testing/selftests/proc/Makefile b/tools/testing/selftests/proc/Makefile index b12921b9794b..c6f7046b9860 100644 --- a/tools/testing/selftests/proc/Makefile +++ b/tools/testing/selftests/proc/Makefile @@ -27,5 +27,6 @@ TEST_GEN_PROGS += setns-sysvipc TEST_GEN_PROGS += thread-self TEST_GEN_PROGS += proc-multiple-procfs TEST_GEN_PROGS += proc-fsconfig-hidepid +TEST_GEN_PROGS += proc-pidns
include ../lib.mk diff --git a/tools/testing/selftests/proc/proc-pidns.c b/tools/testing/selftests/proc/proc-pidns.c new file mode 100644 index 000000000000..f7dd80a2c150 --- /dev/null +++ b/tools/testing/selftests/proc/proc-pidns.c @@ -0,0 +1,315 @@ +// SPDX-License-Identifier: GPL-2.0-or-later +/* + * Author: Aleksa Sarai cyphar@cyphar.com + * Copyright (C) 2025 SUSE LLC. + */ + +#include <assert.h> +#include <errno.h> +#include <sched.h> +#include <stdbool.h> +#include <stdlib.h> +#include <string.h> +#include <unistd.h> +#include <stdio.h> +#include <sys/mount.h> +#include <sys/stat.h> +#include <sys/ioctl.h> +#include <sys/prctl.h> + +#include "../kselftest_harness.h" + +#define ASSERT_ERRNO(expected, _t, seen) \ + __EXPECT(expected, #expected, \ + ({__typeof__(seen) _tmp_seen = (seen); \ + _tmp_seen >= 0 ? _tmp_seen : -errno; }), #seen, _t, 1) + +#define ASSERT_ERRNO_EQ(expected, seen) \ + ASSERT_ERRNO(expected, ==, seen) + +#define ASSERT_SUCCESS(seen) \ + ASSERT_ERRNO(0, <=, seen) + +static int touch(char *path) +{ + int fd = open(path, O_WRONLY|O_CREAT|O_CLOEXEC, 0644); + if (fd < 0) + return -1; + return close(fd); +} + +FIXTURE(ns) +{ + int host_mntns, host_pidns; + int dummy_pidns; +}; + +FIXTURE_SETUP(ns) +{ + /* Stash the old mntns. */ + self->host_mntns = open("/proc/self/ns/mnt", O_RDONLY|O_CLOEXEC); + ASSERT_SUCCESS(self->host_mntns); + + /* Create a new mount namespace and make it private. */ + ASSERT_SUCCESS(unshare(CLONE_NEWNS)); + ASSERT_SUCCESS(mount(NULL, "/", NULL, MS_PRIVATE|MS_REC, NULL)); + + /* + * Create a proper tmpfs that we can use and will disappear once we + * leave this mntns. + */ + ASSERT_SUCCESS(mount("tmpfs", "/tmp", "tmpfs", 0, NULL)); + + /* + * Create a pidns we can use for later tests. We need to fork off a + * child so that we get a usable nsfd that we can bind-mount and open. + */ + ASSERT_SUCCESS(mkdir("/tmp/dummy", 0755)); + ASSERT_SUCCESS(touch("/tmp/dummy/pidns")); + ASSERT_SUCCESS(mkdir("/tmp/dummy/proc", 0755)); + + self->host_pidns = open("/proc/self/ns/pid", O_RDONLY|O_CLOEXEC); + ASSERT_SUCCESS(self->host_pidns); + ASSERT_SUCCESS(unshare(CLONE_NEWPID)); + + pid_t pid = fork(); + ASSERT_SUCCESS(pid); + if (!pid) { + prctl(PR_SET_PDEATHSIG, SIGKILL); + ASSERT_SUCCESS(mount("/proc/self/ns/pid", "/tmp/dummy/pidns", NULL, MS_BIND, NULL)); + ASSERT_SUCCESS(mount("proc", "/tmp/dummy/proc", "proc", 0, NULL)); + exit(0); + } + + int wstatus; + ASSERT_EQ(waitpid(pid, &wstatus, 0), pid); + ASSERT_TRUE(WIFEXITED(wstatus)); + ASSERT_EQ(WEXITSTATUS(wstatus), 0); + + ASSERT_SUCCESS(setns(self->host_pidns, CLONE_NEWPID)); + + self->dummy_pidns = open("/tmp/dummy/pidns", O_RDONLY|O_CLOEXEC); + ASSERT_SUCCESS(self->dummy_pidns); +} + +FIXTURE_TEARDOWN(ns) +{ + ASSERT_SUCCESS(setns(self->host_mntns, CLONE_NEWNS)); + ASSERT_SUCCESS(close(self->host_mntns)); + + ASSERT_SUCCESS(close(self->host_pidns)); + ASSERT_SUCCESS(close(self->dummy_pidns)); +} + +TEST_F(ns, pidns_mount_string_path) +{ + ASSERT_SUCCESS(mkdir("/tmp/proc-host", 0755)); + ASSERT_SUCCESS(mount("proc", "/tmp/proc-host", "proc", 0, "pidns=/proc/self/ns/pid")); + ASSERT_SUCCESS(access("/tmp/proc-host/self/", X_OK)); + + ASSERT_SUCCESS(mkdir("/tmp/proc-dummy", 0755)); + ASSERT_SUCCESS(mount("proc", "/tmp/proc-dummy", "proc", 0, "pidns=/tmp/dummy/pidns")); + ASSERT_ERRNO_EQ(-ENOENT, access("/tmp/proc-dummy/1/", X_OK)); + ASSERT_ERRNO_EQ(-ENOENT, access("/tmp/proc-dummy/self/", X_OK)); +} + +TEST_F(ns, pidns_fsconfig_string_path) +{ + int fsfd = fsopen("proc", FSOPEN_CLOEXEC); + ASSERT_SUCCESS(fsfd); + + ASSERT_SUCCESS(fsconfig(fsfd, FSCONFIG_SET_STRING, "pidns", "/tmp/dummy/pidns", 0)); + ASSERT_SUCCESS(fsconfig(fsfd, FSCONFIG_CMD_CREATE, NULL, NULL, 0)); + + int mountfd = fsmount(fsfd, FSMOUNT_CLOEXEC, 0); + ASSERT_SUCCESS(mountfd); + + ASSERT_ERRNO_EQ(-ENOENT, faccessat(mountfd, "1/", X_OK, 0)); + ASSERT_ERRNO_EQ(-ENOENT, faccessat(mountfd, "self/", X_OK, 0)); + + ASSERT_SUCCESS(close(fsfd)); + ASSERT_SUCCESS(close(mountfd)); +} + +TEST_F(ns, pidns_fsconfig_fd) +{ + int fsfd = fsopen("proc", FSOPEN_CLOEXEC); + ASSERT_SUCCESS(fsfd); + + ASSERT_SUCCESS(fsconfig(fsfd, FSCONFIG_SET_FD, "pidns", NULL, self->dummy_pidns)); + ASSERT_SUCCESS(fsconfig(fsfd, FSCONFIG_CMD_CREATE, NULL, NULL, 0)); + + int mountfd = fsmount(fsfd, FSMOUNT_CLOEXEC, 0); + ASSERT_SUCCESS(mountfd); + + ASSERT_ERRNO_EQ(-ENOENT, faccessat(mountfd, "1/", X_OK, 0)); + ASSERT_ERRNO_EQ(-ENOENT, faccessat(mountfd, "self/", X_OK, 0)); + + ASSERT_SUCCESS(close(fsfd)); + ASSERT_SUCCESS(close(mountfd)); +} + +TEST_F(ns, pidns_reconfigure_remount) +{ + ASSERT_SUCCESS(mkdir("/tmp/proc", 0755)); + ASSERT_SUCCESS(mount("proc", "/tmp/proc", "proc", 0, "")); + + ASSERT_SUCCESS(access("/tmp/proc/1/", X_OK)); + ASSERT_SUCCESS(access("/tmp/proc/self/", X_OK)); + + ASSERT_ERRNO_EQ(-EBUSY, mount(NULL, "/tmp/proc", NULL, MS_REMOUNT, "pidns=/tmp/dummy/pidns")); + + ASSERT_SUCCESS(access("/tmp/proc/1/", X_OK)); + ASSERT_SUCCESS(access("/tmp/proc/self/", X_OK)); +} + +TEST_F(ns, pidns_reconfigure_fsconfig_string_path) +{ + int fsfd = fsopen("proc", FSOPEN_CLOEXEC); + ASSERT_SUCCESS(fsfd); + + ASSERT_SUCCESS(fsconfig(fsfd, FSCONFIG_CMD_CREATE, NULL, NULL, 0)); + + int mountfd = fsmount(fsfd, FSMOUNT_CLOEXEC, 0); + ASSERT_SUCCESS(mountfd); + + ASSERT_SUCCESS(faccessat(mountfd, "1/", X_OK, 0)); + ASSERT_SUCCESS(faccessat(mountfd, "self/", X_OK, 0)); + + ASSERT_ERRNO_EQ(-EBUSY, fsconfig(fsfd, FSCONFIG_SET_STRING, "pidns", "/tmp/dummy/pidns", 0)); + ASSERT_SUCCESS(fsconfig(fsfd, FSCONFIG_CMD_RECONFIGURE, NULL, NULL, 0)); /* noop */ + + ASSERT_SUCCESS(faccessat(mountfd, "1/", X_OK, 0)); + ASSERT_SUCCESS(faccessat(mountfd, "self/", X_OK, 0)); + + ASSERT_SUCCESS(close(fsfd)); + ASSERT_SUCCESS(close(mountfd)); +} + +TEST_F(ns, pidns_reconfigure_fsconfig_fd) +{ + int fsfd = fsopen("proc", FSOPEN_CLOEXEC); + ASSERT_SUCCESS(fsfd); + + ASSERT_SUCCESS(fsconfig(fsfd, FSCONFIG_CMD_CREATE, NULL, NULL, 0)); + + int mountfd = fsmount(fsfd, FSMOUNT_CLOEXEC, 0); + ASSERT_SUCCESS(mountfd); + + ASSERT_SUCCESS(faccessat(mountfd, "1/", X_OK, 0)); + ASSERT_SUCCESS(faccessat(mountfd, "self/", X_OK, 0)); + + ASSERT_ERRNO_EQ(-EBUSY, fsconfig(fsfd, FSCONFIG_SET_FD, "pidns", NULL, self->dummy_pidns)); + ASSERT_SUCCESS(fsconfig(fsfd, FSCONFIG_CMD_RECONFIGURE, NULL, NULL, 0)); /* noop */ + + ASSERT_SUCCESS(faccessat(mountfd, "1/", X_OK, 0)); + ASSERT_SUCCESS(faccessat(mountfd, "self/", X_OK, 0)); + + ASSERT_SUCCESS(close(fsfd)); + ASSERT_SUCCESS(close(mountfd)); +} + +int is_same_inode(int fd1, int fd2) +{ + struct stat stat1, stat2; + + assert(fstat(fd1, &stat1) == 0); + assert(fstat(fd2, &stat2) == 0); + + return stat1.st_ino == stat2.st_ino && stat1.st_dev == stat2.st_dev; +} + +#define PROCFS_IOCTL_MAGIC 'f' +#define PROCFS_GET_PID_NAMESPACE _IO(PROCFS_IOCTL_MAGIC, 32) + +TEST_F(ns, host_get_pidns_ioctl) +{ + int procfs = open("/proc", O_RDONLY|O_CLOEXEC); + ASSERT_SUCCESS(procfs); + + int procfs_pidns = ioctl(procfs, PROCFS_GET_PID_NAMESPACE); + ASSERT_SUCCESS(procfs_pidns); + + ASSERT_TRUE(is_same_inode(self->host_pidns, procfs_pidns)); + ASSERT_FALSE(is_same_inode(self->dummy_pidns, procfs_pidns)); + + ASSERT_SUCCESS(close(procfs)); + ASSERT_SUCCESS(close(procfs_pidns)); +} + +TEST_F(ns, mount_implicit_get_pidns_ioctl) +{ + int procfs = open("/tmp/dummy/proc", O_RDONLY|O_CLOEXEC); + ASSERT_SUCCESS(procfs); + + int procfs_pidns = ioctl(procfs, PROCFS_GET_PID_NAMESPACE); + ASSERT_SUCCESS(procfs_pidns); + + ASSERT_FALSE(is_same_inode(self->host_pidns, procfs_pidns)); + ASSERT_TRUE(is_same_inode(self->dummy_pidns, procfs_pidns)); + + ASSERT_SUCCESS(close(procfs)); + ASSERT_SUCCESS(close(procfs_pidns)); +} + +TEST_F(ns, mount_pidns_get_pidns_ioctl) +{ + ASSERT_SUCCESS(mkdir("/tmp/proc-host", 0755)); + ASSERT_SUCCESS(mount("proc", "/tmp/proc-host", "proc", 0, "pidns=/proc/self/ns/pid")); + + int host_procfs = open("/tmp/proc-host", O_RDONLY|O_CLOEXEC); + ASSERT_SUCCESS(host_procfs); + int host_procfs_pidns = ioctl(host_procfs, PROCFS_GET_PID_NAMESPACE); + ASSERT_SUCCESS(host_procfs_pidns); + + ASSERT_TRUE(is_same_inode(self->host_pidns, host_procfs_pidns)); + ASSERT_FALSE(is_same_inode(self->dummy_pidns, host_procfs_pidns)); + + ASSERT_SUCCESS(mkdir("/tmp/proc-dummy", 0755)); + ASSERT_SUCCESS(mount("proc", "/tmp/proc-dummy", "proc", 0, "pidns=/tmp/dummy/pidns")); + + int dummy_procfs = open("/tmp/proc-dummy", O_RDONLY|O_CLOEXEC); + ASSERT_SUCCESS(dummy_procfs); + int dummy_procfs_pidns = ioctl(dummy_procfs, PROCFS_GET_PID_NAMESPACE); + ASSERT_SUCCESS(dummy_procfs_pidns); + + ASSERT_FALSE(is_same_inode(self->host_pidns, dummy_procfs_pidns)); + ASSERT_TRUE(is_same_inode(self->dummy_pidns, dummy_procfs_pidns)); + + ASSERT_SUCCESS(close(host_procfs)); + ASSERT_SUCCESS(close(host_procfs_pidns)); + ASSERT_SUCCESS(close(dummy_procfs)); + ASSERT_SUCCESS(close(dummy_procfs_pidns)); +} + +TEST_F(ns, fsconfig_pidns_get_pidns_ioctl) +{ + int fsfd = fsopen("proc", FSOPEN_CLOEXEC); + ASSERT_SUCCESS(fsfd); + + ASSERT_SUCCESS(fsconfig(fsfd, FSCONFIG_SET_FD, "pidns", NULL, self->dummy_pidns)); + ASSERT_SUCCESS(fsconfig(fsfd, FSCONFIG_CMD_CREATE, NULL, NULL, 0)); + + int mountfd = fsmount(fsfd, FSMOUNT_CLOEXEC, 0); + ASSERT_SUCCESS(mountfd); + + /* fsmount returns an O_PATH, which ioctl(2) doesn't accept. */ + int new_mountfd = openat(mountfd, ".", O_RDONLY|O_DIRECTORY|O_CLOEXEC); + ASSERT_SUCCESS(new_mountfd); + + ASSERT_SUCCESS(close(mountfd)); + mountfd = -EBADF; + + int procfs_pidns = ioctl(new_mountfd, PROCFS_GET_PID_NAMESPACE); + ASSERT_SUCCESS(procfs_pidns); + + ASSERT_NE(self->dummy_pidns, procfs_pidns); + ASSERT_FALSE(is_same_inode(self->host_pidns, procfs_pidns)); + ASSERT_TRUE(is_same_inode(self->dummy_pidns, procfs_pidns)); + + ASSERT_SUCCESS(close(fsfd)); + ASSERT_SUCCESS(close(new_mountfd)); + ASSERT_SUCCESS(close(procfs_pidns)); +} + +TEST_HARNESS_MAIN
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Aleksa Sarai -
Askar Safin -
Christian Brauner -
Randy Dunlap