Patch "sound/oss: fix deadlock in sequencer_ioctl(SNDCTL_SEQ_OUTOFBAND)" has been added to the 4.0-stable tree

This is a note to let you know that I've just added the patch titled

sound/oss: fix deadlock in sequencer_ioctl(SNDCTL_SEQ_OUTOFBAND)

to the 4.0-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
sound-oss-fix-deadlock-in-sequencer_ioctl-sndctl_seq_outofband.patch
and it can be found in the queue-4.0 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Alexey Khoroshilov <[email protected]>
Date: Sat, 18 Apr 2015 02:53:25 +0300
Subject: sound/oss: fix deadlock in sequencer_ioctl(SNDCTL_SEQ_OUTOFBAND)

From: Alexey Khoroshilov <[email protected]>

commit bc26d4d06e337ade069f33d3f4377593b24e6e36 upstream.

A deadlock can be initiated by userspace via ioctl(SNDCTL_SEQ_OUTOFBAND) on /dev/sequencer with TMR_ECHO midi event.

In this case the control flow is:
sound_ioctl()
-> case SND_DEV_SEQ:
case SND_DEV_SEQ2:

     sequencer_ioctl()
     -> case SNDCTL_SEQ_OUTOFBAND:
          spin_lock_irqsave(&lock,flags);
          play_event();
          -> case EV_TIMING:
               seq_timing_event()
               -> case TMR_ECHO:
                    seq_copy_to_input()
                    -> spin_lock_irqsave(&lock,flags);

It seems that spin_lock_irqsave() around play_event() is not necessary, because the only other call location in seq_startplay() makes the call without acquiring spinlock.

So, the patch just removes spinlocks around play_event(). By the way, it removes unreachable code in seq_timing_event(), since (seq_mode == SEQ_2) case is handled in the beginning.

Compile tested only.

Found by Linux Driver Verification project (linuxtesting.org).

---
 sound/oss/sequencer.c |   12 ++----------
 1 file changed, 2 insertions(+), 10 deletions(-)

@@ -681,13 +681,8 @@ static int seq_timing_event(unsigned cha
 			break;
 
 		case TMR_ECHO:
-			if (seq_mode == SEQ_2)
-				seq_copy_to_input(event_rec, 8);
-			else
-			{
-				parm = (parm << 8 | SEQ_ECHO);
-				seq_copy_to_input((unsigned char *) &parm, 4);
-			}
+			parm = (parm << 8 | SEQ_ECHO);
+			seq_copy_to_input((unsigned char *) &parm, 4);
 			break;
 
 		default:;

@@ -1324,7 +1319,6 @@ int sequencer_ioctl(int dev, struct file
 	int mode = translate_mode(file);
 	struct synth_info inf;
 	struct seq_event_rec event_rec;
-	unsigned long flags;
 	int __user *p = arg;
 
 	orig_dev = dev = dev >> 4;

@@ -1479,9 +1473,7 @@ int sequencer_ioctl(int dev, struct file
 		case SNDCTL_SEQ_OUTOFBAND:
 			if (copy_from_user(&event_rec, arg, sizeof(event_rec)))
 				return -EFAULT;
-			spin_lock_irqsave(&lock,flags);
 			play_event(event_rec.arr);
-			spin_unlock_irqrestore(&lock,flags);
 			return 0;
 
 		case SNDCTL_MIDI_INFO:

Patches currently in stable-queue which might be from [email protected] are

queue-4.0/sound-oss-fix-deadlock-in-sequencer_ioctl-sndctl_seq_outofband.patch