Commit bc26d4d0 authored Apr 18, 2015 by Alexey Khoroshilov Committed by Takashi Iwai Apr 18, 2015

sound/oss: fix deadlock in sequencer_ioctl(SNDCTL_SEQ_OUTOFBAND)



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).

Signed-off-by: Alexey Khoroshilov <khoroshilov@ispras.ru>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

parent 43c499dc

sound/oss/sequencer.c

+2 −10

Original line number	Diff line number	Diff line
		@@ -681,13 +681,8 @@ static int seq_timing_event(unsigned char *event_rec)
		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);
		}
		break;

		default:;
		@@ -1324,7 +1319,6 @@ int sequencer_ioctl(int dev, struct file file, unsigned int cmd, void __user a
		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 file, unsigned int cmd, void __user a
		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: