On Thu, Jul 13, 2023 at 03:01:24PM +0200, Thomas Weißschuh wrote:
On 2023-07-13 22:19:04+1000, Aleksa Sarai wrote:
Due to an oversight in commit 1b3044e39a89 ("procfs: fix pthread cross-thread naming if !PR_DUMPABLE") in switching from REG to NOD, chmod operations on /proc/thread-self/comm were no longer blocked as they are on almost all other procfs files.
A very similar situation with /proc/self/environ was used to as a root exploit a long time ago, but procfs has SB_I_NOEXEC so this is simply a correctness issue.
Ref: https://lwn.net/Articles/191954/ Ref: 6d76fa58b050 ("Don't allow chmod() on the /proc/<pid>/ files") Fixes: 1b3044e39a89 ("procfs: fix pthread cross-thread naming if !PR_DUMPABLE") Cc: stable@vger.kernel.org # v4.7+ Signed-off-by: Aleksa Sarai cyphar@cyphar.com
fs/proc/base.c | 3 ++- tools/testing/selftests/nolibc/nolibc-test.c | 4 ++++ 2 files changed, 6 insertions(+), 1 deletion(-)
diff --git a/fs/proc/base.c b/fs/proc/base.c index 05452c3b9872..7394229816f3 100644 --- a/fs/proc/base.c +++ b/fs/proc/base.c @@ -3583,7 +3583,8 @@ static int proc_tid_comm_permission(struct mnt_idmap *idmap, } static const struct inode_operations proc_tid_comm_inode_operations = {
.permission = proc_tid_comm_permission,
.setattr = proc_setattr,.permission = proc_tid_comm_permission,};
Given that this seems to be a recurring theme a more systematic aproach would help.
Something like the following (untested) patch:
diff --git a/fs/proc/base.c b/fs/proc/base.c index 05452c3b9872..b90f2e9cda66 100644 --- a/fs/proc/base.c +++ b/fs/proc/base.c @@ -2649,6 +2649,7 @@ static struct dentry *proc_pident_instantiate(struct dentry *dentry, set_nlink(inode, 2); /* Use getattr to fix if necessary */ if (p->iop) inode->i_op = p->iop;
- WARN_ON(!inode->i_op->setattr);
Hm, no. This is hacky.
To fix this properly we will need to wean off notify_change() from falling back to simple_setattr() when no i_op->setattr() method is defined. To do that we will have to go through every filesystem and port all that rely on this fallback to set simple_setattr() explicitly as their i_op->setattr() method.
Christoph and I just discussed this in relation to another patch.
This is a bugfix so it should be as minimal as possible for easy backport.