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| author | Takashi Iwai <tiwai@suse.de> | 2016-07-04 14:02:15 +0200 |
|---|---|---|
| committer | Ben Hutchings <ben@decadent.org.uk> | 2016-08-22 22:38:26 +0100 |
| commit | cb2955d6be6202b181a3598f32013ae68cf31b53 (patch) | |
| tree | d3e29486362db230f11d83cc37f0feb0fd4344e9 /sound | |
| parent | 54e5acf19caeb9c0c3bbee2e20cfe6b0e4501a1b (diff) | |
| download | linux-stable-cb2955d6be6202b181a3598f32013ae68cf31b53.tar.gz linux-stable-cb2955d6be6202b181a3598f32013ae68cf31b53.tar.bz2 linux-stable-cb2955d6be6202b181a3598f32013ae68cf31b53.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: Ben Hutchings <ben@decadent.org.uk>
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 17538961e357..7dfb741a91b4 100644 --- a/sound/core/timer.c +++ b/sound/core/timer.c @@ -1965,6 +1965,7 @@ 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) { @@ -1978,7 +1979,6 @@ 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; |