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Subject[tip:core/urgent] futex: Fix handling of bad requeue syscall pairing
Commit-ID:  392741e0a4e17c82e3978b7fcbf04291294dc0a1
Gitweb: http://git.kernel.org/tip/392741e0a4e17c82e3978b7fcbf04291294dc0a1
Author: Darren Hart <dvhltc@us.ibm.com>
AuthorDate: Fri, 7 Aug 2009 15:20:48 -0700
Committer: Ingo Molnar <mingo@elte.hu>
CommitDate: Mon, 10 Aug 2009 20:38:11 +0200

futex: Fix handling of bad requeue syscall pairing

If futex_requeue(requeue_pi=1) finds a futex_q that was created by a call
other the futex_wait_requeue_pi(), the q.rt_waiter may be null. If so,
this will result in an oops from the following call graph:

futex_requeue()
rt_mutex_start_proxy_lock()
task_blocks_on_rt_mutex()
waiter->task dereference
OOPS

We currently WARN_ON() if this is detected, clearly this is inadequate.
If we detect a mispairing in futex_requeue(), bail out, seding -EINVAL to
user-space.

V2: Fix parenthesis warnings.

Signed-off-by: Darren Hart <dvhltc@us.ibm.com>
Acked-by: Peter Zijlstra <peterz@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: John Kacur <jkacur@redhat.com>
Cc: Eric Dumazet <eric.dumazet@gmail.com>
Cc: Dinakar Guniguntala <dino@in.ibm.com>
Cc: John Stultz <johnstul@linux.vnet.ibm.com>
LKML-Reference: <4A7CA8C0.7010809@us.ibm.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>


---
kernel/futex.c | 11 +++++++++--
1 files changed, 9 insertions(+), 2 deletions(-)
diff --git a/kernel/futex.c b/kernel/futex.c
index 8cc3ee1..e18cfbd 100644
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -1256,8 +1256,15 @@ retry_private:
if (!match_futex(&this->key, &key1))
continue;

- WARN_ON(!requeue_pi && this->rt_waiter);
- WARN_ON(requeue_pi && !this->rt_waiter);
+ /*
+ * FUTEX_WAIT_REQEUE_PI and FUTEX_CMP_REQUEUE_PI should always
+ * be paired with each other and no other futex ops.
+ */
+ if ((requeue_pi && !this->rt_waiter) ||
+ (!requeue_pi && this->rt_waiter)) {
+ ret = -EINVAL;
+ break;
+ }

/*
* Wake nr_wake waiters. For requeue_pi, if we acquired the

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