diff options
| author | Davidlohr Bueso <dave@stgolabs.net> | 2026-05-07 14:29:13 +0300 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2026-06-19 14:48:05 +0300 |
| commit | 55363fa0a04524d11efeaadee734d2db1756ed27 (patch) | |
| tree | 6b45f29fed6e9e62ebbf50176453dbf8ed9af2ff | |
| parent | 030bbc857bd51d4b25a90d931d3f8775ef22823a (diff) | |
| download | linux-55363fa0a04524d11efeaadee734d2db1756ed27.tar.xz | |
locking/rtmutex: Skip remove_waiter() when waiter is not enqueued
commit 40a25d59e85b3c8709ac2424d44f65610467871e upstream.
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
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
| -rw-r--r-- | kernel/locking/rtmutex.c | 3 | ||||
| -rw-r--r-- | kernel/locking/rtmutex_api.c | 2 |
2 files changed, 4 insertions, 1 deletions
diff --git a/kernel/locking/rtmutex.c b/kernel/locking/rtmutex.c index e6c6dd086887..fb67482438f8 100644 --- a/kernel/locking/rtmutex.c +++ b/kernel/locking/rtmutex.c @@ -1548,6 +1548,9 @@ 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 59dbd29cb219..0ca695f517d5 100644 --- a/kernel/locking/rtmutex_api.c +++ b/kernel/locking/rtmutex_api.c @@ -365,7 +365,7 @@ 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); |