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| author | Takashi Iwai <tiwai@suse.de> | 2016-07-04 14:02:15 +0200 |
|---|---|---|
| committer | Sasha Levin <alexander.levin@verizon.com> | 2016-07-19 18:20:25 -0400 |
| commit | a851e568525bde7790c8a2bdd49a0258b02accf7 (patch) | |
| tree | ae41f3f623a455b72f0909bc162c1677edd3de96 /sound | |
| parent | b86ef7ef23554d978422ab49366223932ce976d4 (diff) | |
| download | lwn-a851e568525bde7790c8a2bdd49a0258b02accf7.tar.gz lwn-a851e568525bde7790c8a2bdd49a0258b02accf7.zip | |
ALSA: timer: Fix negative queue usage by racy accesses
[ Upstream commit 3fa6993fef634e05d200d141a85df0b044572364 ]
The user timer tu->qused counter may go to a negative value when
multiple concurrent reads are performed since both the check and the
decrement of tu->qused are done in two individual locked contexts.
This results in bogus read outs, and the endless loop in the
user-space side.
The fix is to move the decrement of the tu->qused counter into the
same spinlock context as the zero-check of the counter.
Cc: <stable@vger.kernel.org>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Sasha Levin <alexander.levin@verizon.com>
Diffstat (limited to 'sound')
| -rw-r--r-- | sound/core/timer.c | 2 |
1 files changed, 1 insertions, 1 deletions
diff --git a/sound/core/timer.c b/sound/core/timer.c index 2fd0dccf8505..5c769ea59b68 100644 --- a/sound/core/timer.c +++ b/sound/core/timer.c @@ -1959,6 +1959,7 @@ static ssize_t snd_timer_user_read(struct file *file, char __user *buffer, qhead = tu->qhead++; tu->qhead %= tu->queue_size; + tu->qused--; spin_unlock_irq(&tu->qlock); if (tu->tread) { @@ -1972,7 +1973,6 @@ static ssize_t snd_timer_user_read(struct file *file, char __user *buffer, } spin_lock_irq(&tu->qlock); - tu->qused--; if (err < 0) goto _error; result += unit; |