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>

1 files 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: