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author | Sebastian Andrzej Siewior <bigeasy@linutronix.de> | 2016-04-15 14:35:39 +0200 |
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committer | Sasha Levin <sasha.levin@oracle.com> | 2016-05-10 12:17:31 -0400 |
commit | 28f83d2daecd97392c9a0580c00853a19a76a8bc (patch) | |
tree | 3936018bfd9dc6dd3d29d6f7bbb3b1ed21dce404 /kernel/module_signing.c | |
parent | 6024877a19556baa28a422ff555c1e1e6058504d (diff) |
futex: Handle unlock_pi race gracefully
[ Upstream commit 89e9e66ba1b3bde9d8ea90566c2aee20697ad681 ]
If userspace calls UNLOCK_PI unconditionally without trying the TID -> 0
transition in user space first then the user space value might not have the
waiters bit set. This opens the following race:
CPU0 CPU1
uval = get_user(futex)
lock(hb)
lock(hb)
futex |= FUTEX_WAITERS
....
unlock(hb)
cmpxchg(futex, uval, newval)
So the cmpxchg fails and returns -EINVAL to user space, which is wrong because
the futex value is valid.
To handle this (yes, yet another) corner case gracefully, check for a flag
change and retry.
[ tglx: Massaged changelog and slightly reworked implementation ]
Fixes: ccf9e6a80d9e ("futex: Make unlock_pi more robust")
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: stable@vger.kernel.org
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: Darren Hart <dvhart@linux.intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1460723739-5195-1-git-send-email-bigeasy@linutronix.de
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Sasha Levin <sasha.levin@oracle.com>
Diffstat (limited to 'kernel/module_signing.c')
0 files changed, 0 insertions, 0 deletions