At Sat, 18 Apr 2015 02:53:25 +0300, Alexey Khoroshilov wrote:

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

Applied, thanks.

Takashi

---

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

diff --git a/sound/oss/sequencer.c b/sound/oss/sequencer.c index c0eea1dfe90f..f19da4b47c1d 100644 --- a/sound/oss/sequencer.c +++ b/sound/oss/sequencer.c @@ -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);
  

• 	}
  

• 	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:

-- 1.9.1