This is a note to let you know that I've just added the patch titled
futex: Fix a race condition between REQUEUE_PI and task death
to the 3.17-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
futex-fix-a-race-condition-between-requeue_pi-and-task-death.patch
and it can be found in the queue-3.17 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From 30a6b8031fe14031ab27c1fa3483cb9780e7f63c Mon Sep 17 00:00:00 2001
From: Brian Silverman <bsilver16384@xxxxxxxxx>
Date: Sat, 25 Oct 2014 20:20:37 -0400
Subject: futex: Fix a race condition between REQUEUE_PI and task death
From: Brian Silverman <bsilver16384@xxxxxxxxx>
commit 30a6b8031fe14031ab27c1fa3483cb9780e7f63c upstream.
free_pi_state and exit_pi_state_list both clean up futex_pi_state's.
exit_pi_state_list takes the hb lock first, and most callers of
free_pi_state do too. requeue_pi doesn't, which means free_pi_state
can free the pi_state out from under exit_pi_state_list. For example:
task A | task B
exit_pi_state_list |
pi_state = |
curr->pi_state_list->next |
| futex_requeue(requeue_pi=1)
| // pi_state is the same as
| // the one in task A
| free_pi_state(pi_state)
| list_del_init(&pi_state->list)
| kfree(pi_state)
list_del_init(&pi_state->list) |
Move the free_pi_state calls in requeue_pi to before it drops the hb
locks which it's already holding.
[ tglx: Removed a pointless free_pi_state() call and the hb->lock held
debugging. The latter comes via a seperate patch ]
Signed-off-by: Brian Silverman <bsilver16384@xxxxxxxxx>
Cc: austin.linux@xxxxxxxxx
Cc: darren@xxxxxxxxxx
Cc: peterz@xxxxxxxxxxxxx
Link: http://lkml.kernel.org/r/1414282837-23092-1-git-send-email-bsilver16384@xxxxxxxxx
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
kernel/futex.c | 22 +++++++++++-----------
1 file changed, 11 insertions(+), 11 deletions(-)
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -641,8 +641,14 @@ static struct futex_pi_state * alloc_pi_
return pi_state;
}
+/*
+ * Must be called with the hb lock held.
+ */
static void free_pi_state(struct futex_pi_state *pi_state)
{
+ if (!pi_state)
+ return;
+
if (!atomic_dec_and_test(&pi_state->refcount))
return;
@@ -1521,15 +1527,6 @@ static int futex_requeue(u32 __user *uad
}
retry:
- if (pi_state != NULL) {
- /*
- * We will have to lookup the pi_state again, so free this one
- * to keep the accounting correct.
- */
- free_pi_state(pi_state);
- pi_state = NULL;
- }
-
ret = get_futex_key(uaddr1, flags & FLAGS_SHARED, &key1, VERIFY_READ);
if (unlikely(ret != 0))
goto out;
@@ -1619,6 +1616,8 @@ retry_private:
case 0:
break;
case -EFAULT:
+ free_pi_state(pi_state);
+ pi_state = NULL;
double_unlock_hb(hb1, hb2);
hb_waiters_dec(hb2);
put_futex_key(&key2);
@@ -1634,6 +1633,8 @@ retry_private:
* exit to complete.
* - The user space value changed.
*/
+ free_pi_state(pi_state);
+ pi_state = NULL;
double_unlock_hb(hb1, hb2);
hb_waiters_dec(hb2);
put_futex_key(&key2);
@@ -1710,6 +1711,7 @@ retry_private:
}
out_unlock:
+ free_pi_state(pi_state);
double_unlock_hb(hb1, hb2);
hb_waiters_dec(hb2);
@@ -1727,8 +1729,6 @@ out_put_keys:
out_put_key1:
put_futex_key(&key1);
out:
- if (pi_state != NULL)
- free_pi_state(pi_state);
return ret ? ret : task_count;
}
Patches currently in stable-queue which might be from bsilver16384@xxxxxxxxx are
queue-3.17/futex-fix-a-race-condition-between-requeue_pi-and-task-death.patch
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