[alsa-devel] [PATCH 1/2] ALSA: pcm: Abort properly at pending signal in OSS read/write loops

[Takashi Iwai]

The loops for read and write in PCM OSS emulation have no proper check
of pending signals, and they keep processing even after user tries to
break.  This results in a very long delay, often seen as RCU stall
when a huge unprocessed bytes remain queued.  The bug could be easily
triggered by syzkaller.

As a simple workaround, this patch adds the proper check of pending
signals and aborts the loop appropriately.

Reported-by: syzbot+993cb4cfcbbff3947c21 at syzkaller.appspotmail.com
Cc: <stable at vger.kernel.org>
Signed-off-by: Takashi Iwai <tiwai at suse.de>
---
 sound/core/oss/pcm_oss.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/sound/core/oss/pcm_oss.c b/sound/core/oss/pcm_oss.c
index ceaa51f76591..e317964bd2ea 100644
--- a/sound/core/oss/pcm_oss.c
+++ b/sound/core/oss/pcm_oss.c
@@ -1381,6 +1381,10 @@ static ssize_t snd_pcm_oss_write1(struct snd_pcm_substream *substream, const cha
 			    tmp != runtime->oss.period_bytes)
 				break;
 		}
+		if (signal_pending(current)) {
+			tmp = -ERESTARTSYS;
+			goto err;
+		}
 	}
 	mutex_unlock(&runtime->oss.params_lock);
 	return xfer;
@@ -1466,6 +1470,10 @@ static ssize_t snd_pcm_oss_read1(struct snd_pcm_substream *substream, char __use
 			bytes -= tmp;
 			xfer += tmp;
 		}
+		if (signal_pending(current)) {
+			tmp = -ERESTARTSYS;
+			goto err;
+		}
 	}
 	mutex_unlock(&runtime->oss.params_lock);
 	return xfer;
-- 
2.15.1