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authorPeter Zijlstra <peterz@infradead.org>2017-03-04 10:27:18 +0100
committerThomas Gleixner <tglx@linutronix.de>2017-03-14 21:45:36 +0100
commitc236c8e95a3d395b0494e7108f0d41cf36ec107c (patch)
tree25c0e83f3b4458fb2982a8470876f99adce29cfe
parent4495c08e84729385774601b5146d51d9e5849f81 (diff)
futex: Fix potential use-after-free in FUTEX_REQUEUE_PI
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 Cc: stable@vger.kernel.org Link: http://lkml.kernel.org/r/20170304093558.801744246@infradead.org Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
-rw-r--r--kernel/futex.c20
1 files changed, 11 insertions, 9 deletions
diff --git a/kernel/futex.c b/kernel/futex.c
index 229a744b1781..3a4775fd7468 100644
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -2815,7 +2815,6 @@ 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;
@@ -2907,6 +2906,8 @@ 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
@@ -2930,18 +2931,19 @@ 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