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author | Manfred Spraul <manfred@colorfullife.com> | 2013-09-03 16:00:08 +0200 |
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committer | Linus Torvalds <torvalds@linux-foundation.org> | 2013-09-03 10:42:56 -0700 |
commit | bebcb928c820d0ee83aca4b192adc195e43e66a2 (patch) | |
tree | 28ad45577c7e65e28938eed04b0459674a11f0e3 /REPORTING-BUGS | |
parent | ec1882a9391c55332ebf3d1654f40b76e4a6c010 (diff) | |
download | linux-bebcb928c820d0ee83aca4b192adc195e43e66a2.tar.gz linux-bebcb928c820d0ee83aca4b192adc195e43e66a2.tar.bz2 linux-bebcb928c820d0ee83aca4b192adc195e43e66a2.zip |
ipc/msg.c: Fix lost wakeup in msgsnd().
The check if the queue is full and adding current to the wait queue of
pending msgsnd() operations (ss_add()) must be atomic.
Otherwise:
- the thread that performs msgsnd() finds a full queue and decides to
sleep.
- the thread that performs msgrcv() first reads all messages from the
queue and then sleeps, because the queue is empty.
- the msgrcv() calls do not perform any wakeups, because the msgsnd()
task has not yet called ss_add().
- then the msgsnd()-thread first calls ss_add() and then sleeps.
Net result: msgsnd() and msgrcv() both sleep forever.
Observed with msgctl08 from ltp with a preemptible kernel.
Fix: Call ipc_lock_object() before performing the check.
The patch also moves security_msg_queue_msgsnd() under ipc_lock_object:
- msgctl(IPC_SET) explicitely mentions that it tries to expunge any
pending operations that are not allowed anymore with the new
permissions. If security_msg_queue_msgsnd() is called without locks,
then there might be races.
- it makes the patch much simpler.
Reported-and-tested-by: Vineet Gupta <Vineet.Gupta1@synopsys.com>
Acked-by: Rik van Riel <riel@redhat.com>
Cc: stable@vger.kernel.org # for 3.11
Signed-off-by: Manfred Spraul <manfred@colorfullife.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'REPORTING-BUGS')
0 files changed, 0 insertions, 0 deletions