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sound/oss: fix deadlock in sequencer_ioctl(SNDCTL_SEQ_OUTOFBAND) 

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).

Signed-off-by: Alexey Khoroshilov <khoroshilov@ispras.ru>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Cc: Willy Tarreau <w@1wt.eu>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Alexey Khoroshilov 2015-04-18 02:53:25 +03:00 committed by Greg Kroah-Hartman
parent 6186ada9e4
commit cccea7f5c4
1 changed files with 2 additions and 10 deletions
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12
sound/oss/sequencer.c
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@ -683,13 +683,8 @@ 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:;
@ -1332,7 +1327,6 @@ 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;
@ -1487,9 +1481,7 @@ 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: