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author | Stefan Richter <stefanr@s5r6.in-berlin.de> | 2008-10-26 11:03:37 (GMT) |
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committer | Stefan Richter <stefanr@s5r6.in-berlin.de> | 2008-10-31 07:48:26 (GMT) |
commit | 638570b54346f140bc09b986d93e76025d35180f (patch) | |
tree | b3ffd423bcabe679cb5d218d9f4d2aed4a9ae50e /security | |
parent | 233976e539a93de1320fc7625b24076b1f9e2c9c (diff) | |
download | linux-fsl-qoriq-638570b54346f140bc09b986d93e76025d35180f.tar.xz |
ieee1394: raw1394: fix possible deadlock in multithreaded clients
Regression in 2.6.28-rc1: When I added the new state_mutex which
prevents corruption of raw1394's internal state when accessed by
multithreaded client applications, the following possible though
highly unlikely deadlock slipped in:
Thread A: Thread B:
- acquire mmap_sem - raw1394_write() or raw1394_ioctl()
- raw1394_mmap() - acquire state_mutex
- acquire state_mutex - copy_to/from_user(), possible page fault:
acquire mmap_sem
The simplest fix is to use mutex_trylock() instead of mutex_lock() in
raw1394_mmap(). This changes the behavior under contention in a way
which is visible to userspace clients. However, since multithreaded
access was entirely buggy before state_mutex was added and libraw1394's
documentation advised application programmers to use a handle only in a
single thread, this change in behaviour should not be an issue in
practice at all.
Since we have to use mutex_trylock() in raw1394_mmap() regardless
whether /dev/raw1394 was opened with O_NONBLOCK or not, we now use
mutex_trylock() unconditionally everywhere for state_mutex, just to have
consistent behavior.
Reported-by: Johannes Weiner <hannes@saeurebad.de>
Signed-off-by: Stefan Richter <stefanr@s5r6.in-berlin.de>
Diffstat (limited to 'security')
0 files changed, 0 insertions, 0 deletions