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authorTakashi Iwai <tiwai@suse.de>2016-07-04 14:02:15 +0200
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2016-07-27 09:47:38 -0700
commit547d982b7eeba37eba90597b2ba675e39dd2177d (patch)
treecd6afb44852e5ff04e27d0c84a80d7bb2bd383f9 /sound
parent02a49fd9d0ecc7956cf76b4f7161f2b463e4d73d (diff)
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>
Diffstat (limited to 'sound')
-rw-r--r--sound/core/timer.c2
1 files changed, 1 insertions, 1 deletions
diff --git a/sound/core/timer.c b/sound/core/timer.c
index b982d1b089bd..7c6155f5865b 100644
--- a/sound/core/timer.c
+++ b/sound/core/timer.c
@@ -1961,6 +1961,7 @@ 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) {
@@ -1974,7 +1975,6 @@ 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;