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Fix rtmutex/futex self-deadlock NULL deref in remove_waiter() ahead of RHEL; bump to 211.30.4

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Andrew Lukoshko 2026-07-08 13:47:06 +00:00
parent 3df1ed4e4b
commit 4f6054905f
3 changed files with 168 additions and 2 deletions
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86
1418-rtmutex-use-waiter-task-in-remove-waiter.patch Normal file
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@ -0,0 +1,86 @@
From 3bfdc63936dd4773109b7b8c280c0f3b5ae7d349 Mon Sep 17 00:00:00 2001
From: Keenan Dong <keenanat2000@gmail.com>
Date: Wed, 8 Apr 2026 16:46:00 +0800
Subject: [PATCH] rtmutex: Use waiter::task instead of current in
remove_waiter()
remove_waiter() is used by the slowlock paths, but it is also used for
proxy-lock rollback in rt_mutex_start_proxy_lock() when invoked from
futex_requeue().
In the latter case waiter::task is not current, but remove_waiter()
operates on current for the dequeue operation. That results in several
problems:
1) the rbtree dequeue happens without waiter::task::pi_lock being held
2) the waiter task's pi_blocked_on state is not cleared, which leaves a
dangling pointer primed for UAF around.
3) rt_mutex_adjust_prio_chain() operates on the wrong top priority waiter
task
Use waiter::task instead of current in all related operations in
remove_waiter() to cure those problems.
[ tglx: Fixup rt_mutex_adjust_prio_chain(), add a comment and amend the
changelog ]
Fixes: 8161239a8bcc ("rtmutex: Simplify PI algorithm and make highest prio task get lock")
Reported-by: Yuan Tan <yuantan098@gmail.com>
Reported-by: Yifan Wu <yifanwucs@gmail.com>
Reported-by: Juefei Pu <tomapufckgml@gmail.com>
Reported-by: Xin Liu <bird@lzu.edu.cn>
Signed-off-by: Keenan Dong <keenanat2000@gmail.com>
Signed-off-by: Thomas Gleixner <tglx@kernel.org>
Cc: stable@vger.kernel.org
(cherry picked from commit 3bfdc63936dd4773109b7b8c280c0f3b5ae7d349)
[AlmaLinux: adapted to a10 (6.12); context/line offsets only. scoped_guard(raw_spinlock, ...) is available in this tree (include/linux/cleanup.h + DEFINE_LOCK_GUARD_1 raw_spinlock in include/linux/spinlock.h), so the upstream form is used verbatim.]
---
kernel/locking/rtmutex.c | 13 ++++++++-----
1 file changed, 8 insertions(+), 5 deletions(-)
diff --git a/kernel/locking/rtmutex.c b/kernel/locking/rtmutex.c
index 4a8df18..e6f305d 100644
--- a/kernel/locking/rtmutex.c
+++ b/kernel/locking/rtmutex.c
@@ -1534,20 +1534,23 @@ static bool rtmutex_spin_on_owner(struct rt_mutex_base *lock,
*
* Must be called with lock->wait_lock held and interrupts disabled. It must
* have just failed to try_to_take_rt_mutex().
+ *
+ * When invoked from rt_mutex_start_proxy_lock() waiter::task != current !
*/
static void __sched remove_waiter(struct rt_mutex_base *lock,
struct rt_mutex_waiter *waiter)
{
bool is_top_waiter = (waiter == rt_mutex_top_waiter(lock));
struct task_struct *owner = rt_mutex_owner(lock);
+ struct task_struct *waiter_task = waiter->task;
struct rt_mutex_base *next_lock;
lockdep_assert_held(&lock->wait_lock);
- raw_spin_lock(&current->pi_lock);
- rt_mutex_dequeue(lock, waiter);
- current->pi_blocked_on = NULL;
- raw_spin_unlock(&current->pi_lock);
+ scoped_guard(raw_spinlock, &waiter_task->pi_lock) {
+ rt_mutex_dequeue(lock, waiter);
+ waiter_task->pi_blocked_on = NULL;
+ }
/*
* Only update priority if the waiter was the highest priority
@@ -1583,7 +1586,7 @@ static void __sched remove_waiter(struct rt_mutex_base *lock,
raw_spin_unlock_irq(&lock->wait_lock);
rt_mutex_adjust_prio_chain(owner, RT_MUTEX_MIN_CHAINWALK, lock,
- next_lock, NULL, current);
+ next_lock, NULL, waiter_task);
raw_spin_lock_irq(&lock->wait_lock);
}
--
2.50.1

70
1420-rtmutex-skip-remove-waiter-when-not-enqueued.patch Normal file
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@ -0,0 +1,70 @@
From 40a25d59e85b3c8709ac2424d44f65610467871e Mon Sep 17 00:00:00 2001
From: Davidlohr Bueso <dave@stgolabs.net>
Date: Thu, 7 May 2026 04:29:13 -0700
Subject: [PATCH] locking/rtmutex: Skip remove_waiter() when waiter is not
enqueued
syzbot triggered the following splat in remove_waiter() via
FUTEX_CMP_REQUEUE_PI:
KASAN: null-ptr-deref in range [0x0000000000000a88-0x0000000000000a8f]
class_raw_spinlock_constructor
remove_waiter+0x159/0x1200 kernel/locking/rtmutex.c:1561
rt_mutex_start_proxy_lock+0x103/0x120
futex_requeue+0x10e4/0x20d0
__x64_sys_futex+0x34f/0x4d0
task_blocks_on_rt_mutex() does not arm the waiter upon deadlock detection,
leaving waiter->task nil, where 3bfdc63936dd ("rtmutex: Use waiter::task instead
of current in remove_waiter()") made this fatal.
Furthermore, rt_mutex_start_proxy_lock() should not be calling into remove_waiter()
upon a successfully grabbing the rtmutex. 1a1fb985f2e2 ("futex: Handle early deadlock
return correctly"), moved the remove_waiter() out of __rt_mutex_start_proxy_lock()
(where 'ret' was only ever 0 or < 0) into the wrapper. Tighten this check to
account for try_to_take_rt_mutex().
Fixes: 3bfdc63936dd ("rtmutex: Use waiter::task instead of current in remove_waiter()")
Reported-by: syzbot+78147abe6c524f183ee9@syzkaller.appspotmail.com
Signed-off-by: Davidlohr Bueso <dave@stgolabs.net>
Signed-off-by: Thomas Gleixner <tglx@kernel.org>
Cc: stable@vger.kernel.org
Closes: https://lore.kernel.org/all/69f114ac.050a0220.ac8b.0003.GAE@google.com/
Link: https://patch.msgid.link/20260507112913.1019537-1-dave@stgolabs.net
(cherry picked from commit 40a25d59e85b3c8709ac2424d44f65610467871e)
[AlmaLinux: adapted to a10 (6.12); context/line offsets only. Both hunks apply: remove_waiter() in kernel/locking/rtmutex.c (depends on waiter_task local from 3bfdc63936dd) and rt_mutex_start_proxy_lock() in kernel/locking/rtmutex_api.c. In this tree __rt_mutex_start_proxy_lock() returns 1 on try_to_take_rt_mutex() success, so the ret<0 tightening is required to avoid calling remove_waiter() on lock acquisition.]
---
kernel/locking/rtmutex.c | 3 +++
kernel/locking/rtmutex_api.c | 2 +-
2 files changed, 4 insertions(+), 1 deletion(-)
diff --git a/kernel/locking/rtmutex.c b/kernel/locking/rtmutex.c
index e6f305d..15111dc 100644
--- a/kernel/locking/rtmutex.c
+++ b/kernel/locking/rtmutex.c
@@ -1547,6 +1547,9 @@ static void __sched remove_waiter(struct rt_mutex_base *lock,
lockdep_assert_held(&lock->wait_lock);
+ if (!waiter_task) /* never enqueued */
+ return;
+
scoped_guard(raw_spinlock, &waiter_task->pi_lock) {
rt_mutex_dequeue(lock, waiter);
waiter_task->pi_blocked_on = NULL;
diff --git a/kernel/locking/rtmutex_api.c b/kernel/locking/rtmutex_api.c
index 6614ccd..341a540 100644
--- a/kernel/locking/rtmutex_api.c
+++ b/kernel/locking/rtmutex_api.c
@@ -347,7 +347,7 @@ int __sched rt_mutex_start_proxy_lock(struct rt_mutex_base *lock,
raw_spin_lock_irq(&lock->wait_lock);
ret = __rt_mutex_start_proxy_lock(lock, waiter, task, &wake_q);
- if (unlikely(ret))
+ if (unlikely(ret < 0))
remove_waiter(lock, waiter);
preempt_disable();
raw_spin_unlock_irq(&lock->wait_lock);
--
2.50.1

14
kernel.spec
View File

@ -176,13 +176,13 @@ Summary: The Linux kernel
%define specrpmversion 6.12.0
%define specversion 6.12.0
%define patchversion 6.12
%define pkgrelease 211.30.3
%define pkgrelease 211.30.4
%define kversion 6
%define tarfile_release 6.12.0-211.7.1.el10_2
# This is needed to do merge window version magic
%define patchlevel 12
# This allows pkg_release to have configurable %%{?dist} tag
%define specrelease 211.30.3%{?buildid}%{?dist}
%define specrelease 211.30.4%{?buildid}%{?dist}
# This defines the kabi tarball version
%define kabiversion 6.12.0-211.7.1.el10_2
@ -1452,6 +1452,8 @@ Patch1414: 1414-fs-smb-client-fix-out-of-bounds-read-in-cifs-sanitize-prepa.patc
Patch1415: 1415-kvm-x86-fix-shadow-paging-use-after-free-due-to-unexpected-gfn.patch
Patch1416: 1416-kvm-x86-fix-shadow-paging-use-after-free-due-to-unexpected-role.patch
Patch1417: 1417-eventpoll-fix-ep-remove-struct-eventpoll-struct-file-uaf.patch
Patch1418: 1418-rtmutex-use-waiter-task-in-remove-waiter.patch
Patch1420: 1420-rtmutex-skip-remove-waiter-when-not-enqueued.patch
# END OF PATCH DEFINITIONS
%description
@ -2626,6 +2628,8 @@ ApplyPatch 1414-fs-smb-client-fix-out-of-bounds-read-in-cifs-sanitize-prepa.patc
ApplyPatch 1415-kvm-x86-fix-shadow-paging-use-after-free-due-to-unexpected-gfn.patch
ApplyPatch 1416-kvm-x86-fix-shadow-paging-use-after-free-due-to-unexpected-role.patch
ApplyPatch 1417-eventpoll-fix-ep-remove-struct-eventpoll-struct-file-uaf.patch
ApplyPatch 1418-rtmutex-use-waiter-task-in-remove-waiter.patch
ApplyPatch 1420-rtmutex-skip-remove-waiter-when-not-enqueued.patch
# END OF PATCH APPLICATIONS
# Any further pre-build tree manipulations happen here.
@ -5130,6 +5134,12 @@ fi\
#
#
%changelog
* Tue Jul 08 2026 Andrew Lukoshko <alukoshko@almalinux.org> - 6.12.0-211.30.4
- Fix rtmutex self-deadlock NULL pointer dereference in remove_waiter() ahead of
RHEL, upstream 3bfdc63936dd + 40a25d59e85b (1418, 1420); the futex_requeue guard
74e144274af3 was dropped, reverted upstream by 39def6d250d3 (the NULL deref is
fully handled by 40a25d59e85b)
* Mon Jul 06 2026 Andrew Lukoshko <alukoshko@almalinux.org> - 6.12.0-211.30.3
- Fix CVE-2026-46242: eventpoll ep_remove struct eventpoll / struct file
use-after-free, adapted from upstream a6dc643c6931 ahead of RHEL (1417)