[PATCH v2 1/5] ALSA: timer: Drop async signal support

[Takashi Iwai <tiwai@xxxxxxx>]

The async signal (SIGIO) support for ALSA timer API has been never
used by real applications, but yet it can be a cause of various
potential deadlocks, as spotted by syzkaller.  Let's drop the feature
as the simplest solution.

Reported-by: syzbot+1ee0910eca9c94f71f25@xxxxxxxxxxxxxxxxxxxxxxxxx
Reported-by: syzbot+49b10793b867871ee26f@xxxxxxxxxxxxxxxxxxxxxxxxx
Reported-by: syzbot+8285e973a41b5aa68902@xxxxxxxxxxxxxxxxxxxxxxxxx
Signed-off-by: Takashi Iwai <tiwai@xxxxxxx>
---
 sound/core/timer.c | 13 -------------
 1 file changed, 13 deletions(-)

diff --git a/sound/core/timer.c b/sound/core/timer.c
index b3214baa8919..4ac3ab2cf575 100644
--- a/sound/core/timer.c
+++ b/sound/core/timer.c
@@ -83,7 +83,6 @@ struct snd_timer_user {
 	unsigned int filter;
 	struct timespec64 tstamp;		/* trigger tstamp */
 	wait_queue_head_t qchange_sleep;
-	struct fasync_struct *fasync;
 	struct mutex ioctl_lock;
 };
 
@@ -1345,7 +1344,6 @@ static void snd_timer_user_interrupt(struct snd_timer_instance *timeri,
 	}
       __wake:
 	spin_unlock(&tu->qlock);
-	kill_fasync(&tu->fasync, SIGIO, POLL_IN);
 	wake_up(&tu->qchange_sleep);
 }
 
@@ -1383,7 +1381,6 @@ static void snd_timer_user_ccallback(struct snd_timer_instance *timeri,
 	spin_lock_irqsave(&tu->qlock, flags);
 	snd_timer_user_append_to_tqueue(tu, &r1);
 	spin_unlock_irqrestore(&tu->qlock, flags);
-	kill_fasync(&tu->fasync, SIGIO, POLL_IN);
 	wake_up(&tu->qchange_sleep);
 }
 
@@ -1453,7 +1450,6 @@ static void snd_timer_user_tinterrupt(struct snd_timer_instance *timeri,
 	spin_unlock(&tu->qlock);
 	if (append == 0)
 		return;
-	kill_fasync(&tu->fasync, SIGIO, POLL_IN);
 	wake_up(&tu->qchange_sleep);
 }
 
@@ -2130,14 +2126,6 @@ static long snd_timer_user_ioctl(struct file *file, unsigned int cmd,
 	return ret;
 }
 
-static int snd_timer_user_fasync(int fd, struct file * file, int on)
-{
-	struct snd_timer_user *tu;
-
-	tu = file->private_data;
-	return fasync_helper(fd, file, on, &tu->fasync);
-}
-
 static ssize_t snd_timer_user_read(struct file *file, char __user *buffer,
 				   size_t count, loff_t *offset)
 {
@@ -2280,7 +2268,6 @@ static const struct file_operations snd_timer_f_ops =
 	.poll =		snd_timer_user_poll,
 	.unlocked_ioctl =	snd_timer_user_ioctl,
 	.compat_ioctl =	snd_timer_user_ioctl_compat,
-	.fasync = 	snd_timer_user_fasync,
 };
 
 /* unregister the system timer */
-- 
2.35.3