Commit 2529727b authored by Takashi Iwai's avatar Takashi Iwai Committed by Kamal Mostafa

ALSA: timer: Fix race at concurrent reads

commit 4dff5c7b 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: default avatarTakashi Iwai <tiwai@suse.de>
[ kamal: backport to 3.13-stable: no tu->disconnected clause ]
Signed-off-by: default avatarKamal Mostafa <kamal@canonical.com>
parent df393c57
...@@ -1891,6 +1891,7 @@ static ssize_t snd_timer_user_read(struct file *file, char __user *buffer, ...@@ -1891,6 +1891,7 @@ static ssize_t snd_timer_user_read(struct file *file, char __user *buffer,
{ {
struct snd_timer_user *tu; struct snd_timer_user *tu;
long result = 0, unit; long result = 0, unit;
int qhead;
int err = 0; int err = 0;
tu = file->private_data; tu = file->private_data;
...@@ -1902,7 +1903,7 @@ static ssize_t snd_timer_user_read(struct file *file, char __user *buffer, ...@@ -1902,7 +1903,7 @@ static ssize_t snd_timer_user_read(struct file *file, char __user *buffer,
if ((file->f_flags & O_NONBLOCK) != 0 || result > 0) { if ((file->f_flags & O_NONBLOCK) != 0 || result > 0) {
err = -EAGAIN; err = -EAGAIN;
break; goto _error;
} }
set_current_state(TASK_INTERRUPTIBLE); set_current_state(TASK_INTERRUPTIBLE);
...@@ -1917,38 +1918,33 @@ static ssize_t snd_timer_user_read(struct file *file, char __user *buffer, ...@@ -1917,38 +1918,33 @@ static ssize_t snd_timer_user_read(struct file *file, char __user *buffer,
if (signal_pending(current)) { if (signal_pending(current)) {
err = -ERESTARTSYS; err = -ERESTARTSYS;
break; goto _error;
} }
} }
qhead = tu->qhead++;
tu->qhead %= tu->queue_size;
spin_unlock_irq(&tu->qlock); spin_unlock_irq(&tu->qlock);
if (err < 0)
goto _error;
if (tu->tread) { if (tu->tread) {
if (copy_to_user(buffer, &tu->tqueue[tu->qhead++], if (copy_to_user(buffer, &tu->tqueue[qhead],
sizeof(struct snd_timer_tread))) { sizeof(struct snd_timer_tread)))
err = -EFAULT; err = -EFAULT;
goto _error;
}
} else { } else {
if (copy_to_user(buffer, &tu->queue[tu->qhead++], if (copy_to_user(buffer, &tu->queue[qhead],
sizeof(struct snd_timer_read))) { sizeof(struct snd_timer_read)))
err = -EFAULT; err = -EFAULT;
goto _error;
}
} }
tu->qhead %= tu->queue_size;
result += unit;
buffer += unit;
spin_lock_irq(&tu->qlock); spin_lock_irq(&tu->qlock);
tu->qused--; tu->qused--;
if (err < 0)
goto _error;
result += unit;
buffer += unit;
} }
spin_unlock_irq(&tu->qlock);
_error: _error:
spin_unlock_irq(&tu->qlock);
return result > 0 ? result : err; return result > 0 ? result : err;
} }
......
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