Commit 8ddffd6c authored by Takashi Iwai's avatar Takashi Iwai Committed by Greg Kroah-Hartman

ALSA: seq: Don't break snd_use_lock_sync() loop by timeout

commit 4e7655fd upstream.

The snd_use_lock_sync() (thus its implementation
snd_use_lock_sync_helper()) has the 5 seconds timeout to break out of
the sync loop.  It was introduced from the beginning, just to be
"safer", in terms of avoiding the stupid bugs.

However, as Ben Hutchings suggested, this timeout rather introduces a
potential leak or use-after-free that was apparently fixed by the
commit 2d7d5400 ("ALSA: seq: Fix race during FIFO resize"):
for example, snd_seq_fifo_event_in() -> snd_seq_event_dup() ->
copy_from_user() could block for a long time, and snd_use_lock_sync()
goes timeout and still leaves the cell at releasing the pool.

For fixing such a problem, we remove the break by the timeout while
still keeping the warning.
Suggested-by: default avatarBen Hutchings <ben.hutchings@codethink.co.uk>
Signed-off-by: default avatarTakashi Iwai <tiwai@suse.de>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent ad4fa65f
......@@ -28,19 +28,16 @@
/* wait until all locks are released */
void snd_use_lock_sync_helper(snd_use_lock_t *lockp, const char *file, int line)
{
int max_count = 5 * HZ;
int warn_count = 5 * HZ;
if (atomic_read(lockp) < 0) {
pr_warn("ALSA: seq_lock: lock trouble [counter = %d] in %s:%d\n", atomic_read(lockp), file, line);
return;
}
while (atomic_read(lockp) > 0) {
if (max_count == 0) {
pr_warn("ALSA: seq_lock: timeout [%d left] in %s:%d\n", atomic_read(lockp), file, line);
break;
}
if (warn_count-- == 0)
pr_warn("ALSA: seq_lock: waiting [%d left] in %s:%d\n", atomic_read(lockp), file, line);
schedule_timeout_uninterruptible(1);
max_count--;
}
}
......
Markdown is supported
0%
or
You are about to add 0 people to the discussion. Proceed with caution.
Finish editing this message first!
Please register or to comment