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authorTakashi Iwai <tiwai@suse.de>2016-02-08 17:26:58 +0100
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2016-02-17 12:31:00 -0800
commit925249d5172a31d7d430fdf364fc9229223c7942 (patch)
treeeb83232c7dbdb3521a51eae640759c406d676861 /sound/core
parentce60478a9959a8e1d1dcc70325e72678e78d85c5 (diff)
ALSA: timer: Fix race at concurrent reads
commit 4dff5c7b7093b19c19d3a100f8a3ad87cb7cd9e7 upstream. snd_timer_user_read() has a potential race among parallel reads, as qhead and qused are updated outside the critical section due to copy_to_user() calls. Move them into the critical section, and also sanitize the relevant code a bit. Signed-off-by: Takashi Iwai <tiwai@suse.de> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'sound/core')
-rw-r--r--sound/core/timer.c34
1 files changed, 15 insertions, 19 deletions
diff --git a/sound/core/timer.c b/sound/core/timer.c
index a011b67cf2b6..87be17112573 100644
--- a/sound/core/timer.c
+++ b/sound/core/timer.c
@@ -1920,6 +1920,7 @@ static ssize_t snd_timer_user_read(struct file *file, char __user *buffer,
{
struct snd_timer_user *tu;
long result = 0, unit;
+ int qhead;
int err = 0;
tu = file->private_data;
@@ -1931,7 +1932,7 @@ static ssize_t snd_timer_user_read(struct file *file, char __user *buffer,
if ((file->f_flags & O_NONBLOCK) != 0 || result > 0) {
err = -EAGAIN;
- break;
+ goto _error;
}
set_current_state(TASK_INTERRUPTIBLE);
@@ -1946,42 +1947,37 @@ static ssize_t snd_timer_user_read(struct file *file, char __user *buffer,
if (tu->disconnected) {
err = -ENODEV;
- break;
+ goto _error;
}
if (signal_pending(current)) {
err = -ERESTARTSYS;
- break;
+ goto _error;
}
}
+ qhead = tu->qhead++;
+ tu->qhead %= tu->queue_size;
spin_unlock_irq(&tu->qlock);
- if (err < 0)
- goto _error;
if (tu->tread) {
- if (copy_to_user(buffer, &tu->tqueue[tu->qhead++],
- sizeof(struct snd_timer_tread))) {
+ if (copy_to_user(buffer, &tu->tqueue[qhead],
+ sizeof(struct snd_timer_tread)))
err = -EFAULT;
- goto _error;
- }
} else {
- if (copy_to_user(buffer, &tu->queue[tu->qhead++],
- sizeof(struct snd_timer_read))) {
+ if (copy_to_user(buffer, &tu->queue[qhead],
+ sizeof(struct snd_timer_read)))
err = -EFAULT;
- goto _error;
- }
}
- tu->qhead %= tu->queue_size;
-
- result += unit;
- buffer += unit;
-
spin_lock_irq(&tu->qlock);
tu->qused--;
+ if (err < 0)
+ goto _error;
+ result += unit;
+ buffer += unit;
}
- spin_unlock_irq(&tu->qlock);
_error:
+ spin_unlock_irq(&tu->qlock);
return result > 0 ? result : err;
}