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Commit 4dff5c7b authored by Takashi Iwai's avatar Takashi Iwai
Browse files

ALSA: timer: Fix race at concurrent reads 



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.

Cc: <stable@vger.kernel.org>
Signed-off-by: default avatarTakashi Iwai <tiwai@suse.de>
parent ed8b1d6d

sound/core/timer.c

+15 −19
Original line number Original line Diff line number Diff line
@@ -1933,6 +1933,7 @@ 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;
@@ -1944,7 +1945,7 @@ 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);
@@ -1959,42 +1960,37 @@ static ssize_t snd_timer_user_read(struct file *file, char __user *buffer, 




			if (tu->disconnected) {

			if (tu->disconnected) {

				err = -ENODEV;

				err = -ENODEV;

				break;

				goto _error;

			}

			}

			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;

}

}