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| author | Takashi Iwai <tiwai@suse.de> | 2016-07-04 14:02:15 +0200 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2016-07-27 08:42:22 -0700 |
| commit | 1c390f3dd65d471b60750168613f5b2e8e0779ab (patch) | |
| tree | bfa27cc061ec26931663dae75db5abdba2ffb230 | |
| parent | b4095aacd5b02a6a2b9bf5bb913f9aede4833161 (diff) | |
| download | lwn-1c390f3dd65d471b60750168613f5b2e8e0779ab.tar.gz lwn-1c390f3dd65d471b60750168613f5b2e8e0779ab.zip | |
ALSA: timer: Fix negative queue usage by racy accesses
commit 3fa6993fef634e05d200d141a85df0b044572364 upstream.
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.
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
| -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 6469bedda2f3..23b73f6ac040 100644 --- a/sound/core/timer.c +++ b/sound/core/timer.c @@ -1954,6 +1954,7 @@ 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) { @@ -1967,7 +1968,6 @@ 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; |