ALSA: timer: fix NULL pointer dereference in read()/ioctl() race

[firefly-linux-kernel-4.4.55.git] / sound / core / timer.c

diff --git a/sound/core/timer.c b/sound/core/timer.c
index 637d034bb084ffcd8865e934de91dca42a3d446d..8de029c17f906160cdc4821ab44e9224a078b831 100644 (file)
--- a/sound/core/timer.c
+++ b/sound/core/timer.c
@@ -1967,6 +1967,7 @@ static ssize_t snd_timer_user_read(struct file *file, char __user *buffer,
                tu->qused--;
                spin_unlock_irq(&tu->qlock);
 
+               mutex_lock(&tu->ioctl_lock);
                if (tu->tread) {
                        if (copy_to_user(buffer, &tu->tqueue[qhead],
                                         sizeof(struct snd_timer_tread)))
@@ -1976,6 +1977,7 @@ static ssize_t snd_timer_user_read(struct file *file, char __user *buffer,
                                         sizeof(struct snd_timer_read)))
                                err = -EFAULT;
                }
+               mutex_unlock(&tu->ioctl_lock);
 
                spin_lock_irq(&tu->qlock);
                if (err < 0)