The quilt patch titled
Subject: mm/page_alloc: fix potential deadlock on zonelist_update_seq seqlock
has been removed from the -mm tree. Its filename was
mm-page_alloc-fix-potential-deadlock-on-zonelist_update_seq-seqlock.patch
This patch was dropped because it was merged into the mm-hotfixes-stable branch
of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
------------------------------------------------------
From: Tetsuo Handa <penguin-kernel(a)I-love.SAKURA.ne.jp>
Subject: mm/page_alloc: fix potential deadlock on zonelist_update_seq seqlock
Date: Tue, 4 Apr 2023 23:31:58 +0900
syzbot is reporting circular locking dependency which involves
zonelist_update_seq seqlock [1], for this lock is checked by memory
allocation requests which do not need to be retried.
One deadlock scenario is kmalloc(GFP_ATOMIC) from an interrupt handler.
CPU0
----
__build_all_zonelists() {
write_seqlock(&zonelist_update_seq); // makes zonelist_update_seq.seqcount odd
// e.g. timer interrupt handler runs at this moment
some_timer_func() {
kmalloc(GFP_ATOMIC) {
__alloc_pages_slowpath() {
read_seqbegin(&zonelist_update_seq) {
// spins forever because zonelist_update_seq.seqcount is odd
}
}
}
}
// e.g. timer interrupt handler finishes
write_sequnlock(&zonelist_update_seq); // makes zonelist_update_seq.seqcount even
}
This deadlock scenario can be easily eliminated by not calling
read_seqbegin(&zonelist_update_seq) from !__GFP_DIRECT_RECLAIM allocation
requests, for retry is applicable to only __GFP_DIRECT_RECLAIM allocation
requests. But Michal Hocko does not know whether we should go with this
approach.
Another deadlock scenario which syzbot is reporting is a race between
kmalloc(GFP_ATOMIC) from tty_insert_flip_string_and_push_buffer() with
port->lock held and printk() from __build_all_zonelists() with
zonelist_update_seq held.
CPU0 CPU1
---- ----
pty_write() {
tty_insert_flip_string_and_push_buffer() {
__build_all_zonelists() {
write_seqlock(&zonelist_update_seq);
build_zonelists() {
printk() {
vprintk() {
vprintk_default() {
vprintk_emit() {
console_unlock() {
console_flush_all() {
console_emit_next_record() {
con->write() = serial8250_console_write() {
spin_lock_irqsave(&port->lock, flags);
tty_insert_flip_string() {
tty_insert_flip_string_fixed_flag() {
__tty_buffer_request_room() {
tty_buffer_alloc() {
kmalloc(GFP_ATOMIC | __GFP_NOWARN) {
__alloc_pages_slowpath() {
zonelist_iter_begin() {
read_seqbegin(&zonelist_update_seq); // spins forever because zonelist_update_seq.seqcount is odd
spin_lock_irqsave(&port->lock, flags); // spins forever because port->lock is held
}
}
}
}
}
}
}
}
spin_unlock_irqrestore(&port->lock, flags);
// message is printed to console
spin_unlock_irqrestore(&port->lock, flags);
}
}
}
}
}
}
}
}
}
write_sequnlock(&zonelist_update_seq);
}
}
}
This deadlock scenario can be eliminated by
preventing interrupt context from calling kmalloc(GFP_ATOMIC)
and
preventing printk() from calling console_flush_all()
while zonelist_update_seq.seqcount is odd.
Since Petr Mladek thinks that __build_all_zonelists() can become a
candidate for deferring printk() [2], let's address this problem by
disabling local interrupts in order to avoid kmalloc(GFP_ATOMIC)
and
disabling synchronous printk() in order to avoid console_flush_all()
.
As a side effect of minimizing duration of zonelist_update_seq.seqcount
being odd by disabling synchronous printk(), latency at
read_seqbegin(&zonelist_update_seq) for both !__GFP_DIRECT_RECLAIM and
__GFP_DIRECT_RECLAIM allocation requests will be reduced. Although, from
lockdep perspective, not calling read_seqbegin(&zonelist_update_seq) (i.e.
do not record unnecessary locking dependency) from interrupt context is
still preferable, even if we don't allow calling kmalloc(GFP_ATOMIC)
inside
write_seqlock(&zonelist_update_seq)/write_sequnlock(&zonelist_update_seq)
section...
Link: https://lkml.kernel.org/r/8796b95c-3da3-5885-fddd-6ef55f30e4d3@I-love.SAKUR…
Fixes: 3d36424b3b58 ("mm/page_alloc: fix race condition between build_all_zonelists and page allocation")
Link: https://lkml.kernel.org/r/ZCrs+1cDqPWTDFNM@alley [2]
Reported-by: syzbot <syzbot+223c7461c58c58a4cb10(a)syzkaller.appspotmail.com>
Link: https://syzkaller.appspot.com/bug?extid=223c7461c58c58a4cb10 [1]
Signed-off-by: Tetsuo Handa <penguin-kernel(a)I-love.SAKURA.ne.jp>
Acked-by: Michal Hocko <mhocko(a)suse.com>
Acked-by: Mel Gorman <mgorman(a)techsingularity.net>
Cc: Petr Mladek <pmladek(a)suse.com>
Cc: David Hildenbrand <david(a)redhat.com>
Cc: Ilpo J��rvinen <ilpo.jarvinen(a)linux.intel.com>
Cc: John Ogness <john.ogness(a)linutronix.de>
Cc: Patrick Daly <quic_pdaly(a)quicinc.com>
Cc: Sergey Senozhatsky <senozhatsky(a)chromium.org>
Cc: Steven Rostedt <rostedt(a)goodmis.org>
Cc: <stable(a)vger.kernel.org>
Signed-off-by: Andrew Morton <akpm(a)linux-foundation.org>
---
mm/page_alloc.c | 16 ++++++++++++++++
1 file changed, 16 insertions(+)
--- a/mm/page_alloc.c~mm-page_alloc-fix-potential-deadlock-on-zonelist_update_seq-seqlock
+++ a/mm/page_alloc.c
@@ -6632,7 +6632,21 @@ static void __build_all_zonelists(void *
int nid;
int __maybe_unused cpu;
pg_data_t *self = data;
+ unsigned long flags;
+ /*
+ * Explicitly disable this CPU's interrupts before taking seqlock
+ * to prevent any IRQ handler from calling into the page allocator
+ * (e.g. GFP_ATOMIC) that could hit zonelist_iter_begin and livelock.
+ */
+ local_irq_save(flags);
+ /*
+ * Explicitly disable this CPU's synchronous printk() before taking
+ * seqlock to prevent any printk() from trying to hold port->lock, for
+ * tty_insert_flip_string_and_push_buffer() on other CPU might be
+ * calling kmalloc(GFP_ATOMIC | __GFP_NOWARN) with port->lock held.
+ */
+ printk_deferred_enter();
write_seqlock(&zonelist_update_seq);
#ifdef CONFIG_NUMA
@@ -6671,6 +6685,8 @@ static void __build_all_zonelists(void *
}
write_sequnlock(&zonelist_update_seq);
+ printk_deferred_exit();
+ local_irq_restore(flags);
}
static noinline void __init
_
Patches currently in -mm which might be from penguin-kernel(a)I-love.SAKURA.ne.jp are
The quilt patch titled
Subject: kernel/sys.c: fix and improve control flow in __sys_setres[ug]id()
has been removed from the -mm tree. Its filename was
kernel-sysc-fix-and-improve-control-flow-in-__sys_setresid.patch
This patch was dropped because it was merged into the mm-hotfixes-stable branch
of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
------------------------------------------------------
From: Ondrej Mosnacek <omosnace(a)redhat.com>
Subject: kernel/sys.c: fix and improve control flow in __sys_setres[ug]id()
Date: Fri, 17 Feb 2023 17:21:54 +0100
Linux Security Modules (LSMs) that implement the "capable" hook will
usually emit an access denial message to the audit log whenever they
"block" the current task from using the given capability based on their
security policy.
The occurrence of a denial is used as an indication that the given task
has attempted an operation that requires the given access permission, so
the callers of functions that perform LSM permission checks must take care
to avoid calling them too early (before it is decided if the permission is
actually needed to perform the requested operation).
The __sys_setres[ug]id() functions violate this convention by first
calling ns_capable_setid() and only then checking if the operation
requires the capability or not. It means that any caller that has the
capability granted by DAC (task's capability set) but not by MAC (LSMs)
will generate a "denied" audit record, even if is doing an operation for
which the capability is not required.
Fix this by reordering the checks such that ns_capable_setid() is checked
last and -EPERM is returned immediately if it returns false.
While there, also do two small optimizations:
* move the capability check before prepare_creds() and
* bail out early in case of a no-op.
Link: https://lkml.kernel.org/r/20230217162154.837549-1-omosnace@redhat.com
Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Signed-off-by: Ondrej Mosnacek <omosnace(a)redhat.com>
Cc: Eric W. Biederman <ebiederm(a)xmission.com>
Cc: <stable(a)vger.kernel.org>
Signed-off-by: Andrew Morton <akpm(a)linux-foundation.org>
---
kernel/sys.c | 69 ++++++++++++++++++++++++++++---------------------
1 file changed, 40 insertions(+), 29 deletions(-)
--- a/kernel/sys.c~kernel-sysc-fix-and-improve-control-flow-in-__sys_setresid
+++ a/kernel/sys.c
@@ -664,6 +664,7 @@ long __sys_setresuid(uid_t ruid, uid_t e
struct cred *new;
int retval;
kuid_t kruid, keuid, ksuid;
+ bool ruid_new, euid_new, suid_new;
kruid = make_kuid(ns, ruid);
keuid = make_kuid(ns, euid);
@@ -678,25 +679,29 @@ long __sys_setresuid(uid_t ruid, uid_t e
if ((suid != (uid_t) -1) && !uid_valid(ksuid))
return -EINVAL;
+ old = current_cred();
+
+ /* check for no-op */
+ if ((ruid == (uid_t) -1 || uid_eq(kruid, old->uid)) &&
+ (euid == (uid_t) -1 || (uid_eq(keuid, old->euid) &&
+ uid_eq(keuid, old->fsuid))) &&
+ (suid == (uid_t) -1 || uid_eq(ksuid, old->suid)))
+ return 0;
+
+ ruid_new = ruid != (uid_t) -1 && !uid_eq(kruid, old->uid) &&
+ !uid_eq(kruid, old->euid) && !uid_eq(kruid, old->suid);
+ euid_new = euid != (uid_t) -1 && !uid_eq(keuid, old->uid) &&
+ !uid_eq(keuid, old->euid) && !uid_eq(keuid, old->suid);
+ suid_new = suid != (uid_t) -1 && !uid_eq(ksuid, old->uid) &&
+ !uid_eq(ksuid, old->euid) && !uid_eq(ksuid, old->suid);
+ if ((ruid_new || euid_new || suid_new) &&
+ !ns_capable_setid(old->user_ns, CAP_SETUID))
+ return -EPERM;
+
new = prepare_creds();
if (!new)
return -ENOMEM;
- old = current_cred();
-
- retval = -EPERM;
- if (!ns_capable_setid(old->user_ns, CAP_SETUID)) {
- if (ruid != (uid_t) -1 && !uid_eq(kruid, old->uid) &&
- !uid_eq(kruid, old->euid) && !uid_eq(kruid, old->suid))
- goto error;
- if (euid != (uid_t) -1 && !uid_eq(keuid, old->uid) &&
- !uid_eq(keuid, old->euid) && !uid_eq(keuid, old->suid))
- goto error;
- if (suid != (uid_t) -1 && !uid_eq(ksuid, old->uid) &&
- !uid_eq(ksuid, old->euid) && !uid_eq(ksuid, old->suid))
- goto error;
- }
-
if (ruid != (uid_t) -1) {
new->uid = kruid;
if (!uid_eq(kruid, old->uid)) {
@@ -761,6 +766,7 @@ long __sys_setresgid(gid_t rgid, gid_t e
struct cred *new;
int retval;
kgid_t krgid, kegid, ksgid;
+ bool rgid_new, egid_new, sgid_new;
krgid = make_kgid(ns, rgid);
kegid = make_kgid(ns, egid);
@@ -773,23 +779,28 @@ long __sys_setresgid(gid_t rgid, gid_t e
if ((sgid != (gid_t) -1) && !gid_valid(ksgid))
return -EINVAL;
+ old = current_cred();
+
+ /* check for no-op */
+ if ((rgid == (gid_t) -1 || gid_eq(krgid, old->gid)) &&
+ (egid == (gid_t) -1 || (gid_eq(kegid, old->egid) &&
+ gid_eq(kegid, old->fsgid))) &&
+ (sgid == (gid_t) -1 || gid_eq(ksgid, old->sgid)))
+ return 0;
+
+ rgid_new = rgid != (gid_t) -1 && !gid_eq(krgid, old->gid) &&
+ !gid_eq(krgid, old->egid) && !gid_eq(krgid, old->sgid);
+ egid_new = egid != (gid_t) -1 && !gid_eq(kegid, old->gid) &&
+ !gid_eq(kegid, old->egid) && !gid_eq(kegid, old->sgid);
+ sgid_new = sgid != (gid_t) -1 && !gid_eq(ksgid, old->gid) &&
+ !gid_eq(ksgid, old->egid) && !gid_eq(ksgid, old->sgid);
+ if ((rgid_new || egid_new || sgid_new) &&
+ !ns_capable_setid(old->user_ns, CAP_SETGID))
+ return -EPERM;
+
new = prepare_creds();
if (!new)
return -ENOMEM;
- old = current_cred();
-
- retval = -EPERM;
- if (!ns_capable_setid(old->user_ns, CAP_SETGID)) {
- if (rgid != (gid_t) -1 && !gid_eq(krgid, old->gid) &&
- !gid_eq(krgid, old->egid) && !gid_eq(krgid, old->sgid))
- goto error;
- if (egid != (gid_t) -1 && !gid_eq(kegid, old->gid) &&
- !gid_eq(kegid, old->egid) && !gid_eq(kegid, old->sgid))
- goto error;
- if (sgid != (gid_t) -1 && !gid_eq(ksgid, old->gid) &&
- !gid_eq(ksgid, old->egid) && !gid_eq(ksgid, old->sgid))
- goto error;
- }
if (rgid != (gid_t) -1)
new->gid = krgid;
_
Patches currently in -mm which might be from omosnace(a)redhat.com are
On Tue, Aug 23, 2022 at 07:20:14AM -0500, Bjorn Helgaas wrote:
> On Tue, Aug 23, 2022, 6:35 AM Greg Kroah-Hartman <gregkh(a)linuxfoundation.org>
> wrote:
>
> > From: Stefan Roese <sr(a)denx.de>
> >
> > [ Upstream commit 8795e182b02dc87e343c79e73af6b8b7f9c5e635 ]
> >
>
> There's an open regression related to this commit:
>
> https://bugzilla.kernel.org/show_bug.cgi?id=216373
This is already in the following released stable kernels:
5.10.137 5.15.61 5.18.18 5.19.2
I'll go drop it from the 4.19 and 5.4 queues, but when this gets
resolved in Linus's tree, make sure there's a cc: stable on the fix so
that we know to backport it to the above branches as well. Or at the
least, a "Fixes:" tag.
thanks,
greg k-h