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authorThomas Gleixner <tglx@linutronix.de>2014-05-12 20:45:34 +0000
committerWilly Tarreau <w@1wt.eu>2014-06-19 00:25:57 +0200
commit81ce5f0cae0c15d679fef2219414bb508c9c1873 (patch)
tree5caf22af721ae7197cc6cf0e2a3ba56b5ace0b42
parentd100b2748ac930237a97646ae9a4721a7f62acc1 (diff)
downloadlinux-linaro-stable-81ce5f0cae0c15d679fef2219414bb508c9c1873.tar.gz
futex: Add another early deadlock detection check
Dave Jones trinity syscall fuzzer exposed an issue in the deadlock detection code of rtmutex: http://lkml.kernel.org/r/20140429151655.GA14277@redhat.com That underlying issue has been fixed with a patch to the rtmutex code, but the futex code must not call into rtmutex in that case because - it can detect that issue early - it avoids a different and more complex fixup for backing out If the user space variable got manipulated to 0x80000000 which means no lock holder, but the waiters bit set and an active pi_state in the kernel is found we can figure out the recursive locking issue by looking at the pi_state owner. If that is the current task, then we can safely return -EDEADLK. The check should have been added in commit 59fa62451 (futex: Handle futex_pi OWNER_DIED take over correctly) already, but I did not see the above issue caused by user space manipulation back then. Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Cc: Dave Jones <davej@redhat.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Darren Hart <darren@dvhart.com> Cc: Davidlohr Bueso <davidlohr@hp.com> Cc: Steven Rostedt <rostedt@goodmis.org> Cc: Clark Williams <williams@redhat.com> Cc: Paul McKenney <paulmck@linux.vnet.ibm.com> Cc: Lai Jiangshan <laijs@cn.fujitsu.com> Cc: Roland McGrath <roland@hack.frob.com> Cc: Carlos ODonell <carlos@redhat.com> Cc: Jakub Jelinek <jakub@redhat.com> Cc: Michael Kerrisk <mtk.manpages@gmail.com> Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de> Link: http://lkml.kernel.org/r/20140512201701.097349971@linutronix.de Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Cc: stable@vger.kernel.org (cherry picked from commit 866293ee54227584ffcb4a42f69c1f365974ba7f) Signed-off-by: Willy Tarreau <w@1wt.eu>
-rw-r--r--kernel/futex.c49
1 files changed, 35 insertions, 14 deletions
diff --git a/kernel/futex.c b/kernel/futex.c
index 9c5ffe1355b0..731b2714e2ba 100644
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -538,7 +538,8 @@ void exit_pi_state_list(struct task_struct *curr)
static int
lookup_pi_state(u32 uval, struct futex_hash_bucket *hb,
- union futex_key *key, struct futex_pi_state **ps)
+ union futex_key *key, struct futex_pi_state **ps,
+ struct task_struct *task)
{
struct futex_pi_state *pi_state = NULL;
struct futex_q *this, *next;
@@ -582,6 +583,16 @@ lookup_pi_state(u32 uval, struct futex_hash_bucket *hb,
return -EINVAL;
}
+ /*
+ * Protect against a corrupted uval. If uval
+ * is 0x80000000 then pid is 0 and the waiter
+ * bit is set. So the deadlock check in the
+ * calling code has failed and we did not fall
+ * into the check above due to !pid.
+ */
+ if (task && pi_state->owner == task)
+ return -EDEADLK;
+
atomic_inc(&pi_state->refcount);
*ps = pi_state;
@@ -737,7 +748,7 @@ retry:
* We dont have the lock. Look up the PI state (or create it if
* we are the first waiter):
*/
- ret = lookup_pi_state(uval, hb, key, ps);
+ ret = lookup_pi_state(uval, hb, key, ps, task);
if (unlikely(ret)) {
switch (ret) {
@@ -1122,8 +1133,8 @@ void requeue_pi_wake_futex(struct futex_q *q, union futex_key *key,
* hb1 and hb2 must be held by the caller.
*
* Returns:
- * 0 - failed to acquire the lock atomicly
- * 1 - acquired the lock
+ * 0 - failed to acquire the lock atomically;
+ * >0 - acquired the lock, return value is vpid of the top_waiter
* <0 - error
*/
static int futex_proxy_trylock_atomic(u32 __user *pifutex,
@@ -1134,7 +1145,7 @@ static int futex_proxy_trylock_atomic(u32 __user *pifutex,
{
struct futex_q *top_waiter = NULL;
u32 curval;
- int ret;
+ int ret, vpid;
if (get_futex_value_locked(&curval, pifutex))
return -EFAULT;
@@ -1162,11 +1173,13 @@ static int futex_proxy_trylock_atomic(u32 __user *pifutex,
* the contended case or if set_waiters is 1. The pi_state is returned
* in ps in contended cases.
*/
+ vpid = task_pid_vnr(top_waiter->task);
ret = futex_lock_pi_atomic(pifutex, hb2, key2, ps, top_waiter->task,
set_waiters);
- if (ret == 1)
+ if (ret == 1) {
requeue_pi_wake_futex(top_waiter, key2, hb2);
-
+ return vpid;
+ }
return ret;
}
@@ -1196,7 +1209,6 @@ static int futex_requeue(u32 __user *uaddr1, int fshared, u32 __user *uaddr2,
struct futex_hash_bucket *hb1, *hb2;
struct plist_head *head1;
struct futex_q *this, *next;
- u32 curval2;
if (requeue_pi) {
/*
@@ -1282,16 +1294,25 @@ retry_private:
* At this point the top_waiter has either taken uaddr2 or is
* waiting on it. If the former, then the pi_state will not
* exist yet, look it up one more time to ensure we have a
- * reference to it.
+ * reference to it. If the lock was taken, ret contains the
+ * vpid of the top waiter task.
*/
- if (ret == 1) {
+ if (ret > 0) {
WARN_ON(pi_state);
drop_count++;
task_count++;
- ret = get_futex_value_locked(&curval2, uaddr2);
- if (!ret)
- ret = lookup_pi_state(curval2, hb2, &key2,
- &pi_state);
+ /*
+ * If we acquired the lock, then the user
+ * space value of uaddr2 should be vpid. It
+ * cannot be changed by the top waiter as it
+ * is blocked on hb2 lock if it tries to do
+ * so. If something fiddled with it behind our
+ * back the pi state lookup might unearth
+ * it. So we rather use the known value than
+ * rereading and handing potential crap to
+ * lookup_pi_state.
+ */
+ ret = lookup_pi_state(ret, hb2, &key2, &pi_state, NULL);
}
switch (ret) {