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SubjectRe: [PATCH] sound/oss: fix deadlock in sequencer_ioctl(SNDCTL_SEQ_OUTOFBAND)
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
>


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