diff options
| author | Peter Zijlstra <peterz@infradead.org> | 2017-03-04 10:27:18 +0100 |
|---|---|---|
| committer | Mister Oyster <oysterized@gmail.com> | 2017-07-04 12:11:04 +0200 |
| commit | 5ade9d300342dc05e249226b6adbd3491ec5984e (patch) | |
| tree | 8f6b14be888ee0c6a523b929e67cda933b850f20 /kernel/futex.c | |
| parent | 0618ff63643a4878b72f33b3d66f37964d618921 (diff) | |
futex: Fix potential use-after-free in FUTEX_REQUEUE_PI
commit c236c8e95a3d395b0494e7108f0d41cf36ec107c upstream.
While working on the futex code, I stumbled over this potential
use-after-free scenario. Dmitry triggered it later with syzkaller.
pi_mutex is a pointer into pi_state, which we drop the reference on in
unqueue_me_pi(). So any access to that pointer after that is bad.
Since other sites already do rt_mutex_unlock() with hb->lock held, see
for example futex_lock_pi(), simply move the unlock before
unqueue_me_pi().
Reported-by: Dmitry Vyukov <dvyukov@google.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Darren Hart <dvhart@linux.intel.com>
Cc: juri.lelli@arm.com
Cc: bigeasy@linutronix.de
Cc: xlpang@redhat.com
Cc: rostedt@goodmis.org
Cc: mathieu.desnoyers@efficios.com
Cc: jdesfossez@efficios.com
Cc: dvhart@infradead.org
Cc: bristot@redhat.com
Link: http://lkml.kernel.org/r/20170304093558.801744246@infradead.org
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Willy Tarreau <w@1wt.eu>
Diffstat (limited to 'kernel/futex.c')
| -rw-r--r-- | kernel/futex.c | 20 |
1 files changed, 11 insertions, 9 deletions
diff --git a/kernel/futex.c b/kernel/futex.c index a26ce0f0b..d80601915 100644 --- a/kernel/futex.c +++ b/kernel/futex.c @@ -2430,7 +2430,6 @@ static int futex_wait_requeue_pi(u32 __user *uaddr, unsigned int flags, { struct hrtimer_sleeper timeout, *to = NULL; struct rt_mutex_waiter rt_waiter; - struct rt_mutex *pi_mutex = NULL; struct futex_hash_bucket *hb; union futex_key key2 = FUTEX_KEY_INIT; struct futex_q q = futex_q_init; @@ -2528,6 +2527,8 @@ static int futex_wait_requeue_pi(u32 __user *uaddr, unsigned int flags, spin_unlock(q.lock_ptr); } } else { + struct rt_mutex *pi_mutex; + /* * We have been woken up by futex_unlock_pi(), a timeout, or a * signal. futex_unlock_pi() will not destroy the lock_ptr nor @@ -2551,18 +2552,19 @@ static int futex_wait_requeue_pi(u32 __user *uaddr, unsigned int flags, if (res) ret = (res < 0) ? res : 0; + /* + * If fixup_pi_state_owner() faulted and was unable to handle + * the fault, unlock the rt_mutex and return the fault to + * userspace. + */ + if (ret && rt_mutex_owner(pi_mutex) == current) + rt_mutex_unlock(pi_mutex); + /* Unqueue and drop the lock. */ unqueue_me_pi(&q); } - /* - * If fixup_pi_state_owner() faulted and was unable to handle the - * fault, unlock the rt_mutex and return the fault to userspace. - */ - if (ret == -EFAULT) { - if (pi_mutex && rt_mutex_owner(pi_mutex) == current) - rt_mutex_unlock(pi_mutex); - } else if (ret == -EINTR) { + if (ret == -EINTR) { /* * We've already been requeued, but cannot restart by calling * futex_lock_pi() directly. We could restart this syscall, but |