Hi Dave,
On 06/10/2014 04:19 PM, Dave Jones wrote:
On Fri, Jun 06, 2014 at 11:50:06PM +0000, Linux Kernel wrote:
> Gitweb:
http://git.kernel.org/linus/;a=commit;h=d198cd6d6d02d0a335af2deacb60816ebb4719d1
> Commit: d198cd6d6d02d0a335af2deacb60816ebb4719d1
> Parent: 2f2ed41dcaec34f2d6f224aa84efcc5a9dd8d5c3
> Refname: refs/heads/next
> Author: Manfred Spraul <manf...@colorfullife.com>
> AuthorDate: Fri Jun 6 14:37:49 2014 -0700
> Committer: Linus Torvalds <torva...@linux-foundation.org>
> CommitDate: Fri Jun 6 16:08:15 2014 -0700
>
> ipc/sem.c: change perform_atomic_semop parameters
>
> Right now, perform_atomic_semop gets the content of sem_queue as
> individual fields. Changes that, instead pass a pointer to sem_queue.
>
> This is a preparation for the next patch: it uses sem_queue to store the
> reason why a task must sleep.
>
> Signed-off-by: Manfred Spraul <manf...@colorfullife.com>
> Cc: Davidlohr Bueso <davidlohr.bu...@hp.com>
> Cc: Michael Kerrisk <mtk.manpa...@gmail.com>
> Signed-off-by: Andrew Morton <a...@linux-foundation.org>
> Signed-off-by: Linus Torvalds <torva...@linux-foundation.org>
After this patch, coverity started complaining about a potential deref
after null check. (It may have been a problem before, but the code motion
causes a new 'event')
33. var_compare_op: Comparing un to null implies that un might be null.
1878 if (un && un->semid == -1)
1879 goto out_unlock_free;
1880
1881 queue.sops = sops;
1882 queue.nsops = nsops;
Correct, un can be NULL.
But only if sem_flg & SEM_UNDO is false for every operation:
from semtimedop():
if (sop->sem_flg & SEM_UNDO)
undos = 1;
[...]
if (undos) {
/* On success, find_alloc_undo takes the
rcu_read_lock */
un = find_alloc_undo(ns, semid);
if (IS_ERR(un)) {
error = PTR_ERR(un);
goto out_free;
}
} else {
un = NULL;
rcu_read_lock();
}
34. alias_transfer: Assigning: queue.undo = un.
1883 queue.undo = un;
1884 queue.pid = task_tgid_vnr(current);
1885 queue.alter = alter;
1886
Correct.
CID 1222114 (#1 of 1): Dereference after null check (FORWARD_NULL)
35. var_deref_model: Passing &queue to perform_atomic_semop, which dereferences
null queue.undo. [show details]
1887 error = perform_atomic_semop(sma, &queue);
Passing &queue to perform_atomic_semop (correct),
which dereferences null queue.undo: Incorrect. queue.undo is only
dereferenced if sem_flg&SEM_UNDO is true.
Thus: As far as I can see it's a false alarm.
And - even more simply: queue.un=NULL is the common case.
--
Manfred
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