The patch below does not apply to the 4.4-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.
thanks,
greg k-h
------------------ original commit in Linus's tree ------------------
From e15dc99dbb9cf99f6432e8e3c0b3a8f7a3403a86 Mon Sep 17 00:00:00 2001
From: Takashi Iwai tiwai@suse.de Date: Sat, 7 Apr 2018 11:48:58 +0200 Subject: [PATCH] ALSA: pcm: Fix endless loop for XRUN recovery in OSS emulation
The commit 02a5d6925cd3 ("ALSA: pcm: Avoid potential races between OSS ioctls and read/write") split the PCM preparation code to a locked version, and it added a sanity check of runtime->oss.prepare flag along with the change. This leaded to an endless loop when the stream gets XRUN: namely, snd_pcm_oss_write3() and co call snd_pcm_oss_prepare() without setting runtime->oss.prepare flag and the loop continues until the PCM state reaches to another one.
As the function is supposed to execute the preparation unconditionally, drop the invalid state check there.
The bug was triggered by syzkaller.
Fixes: 02a5d6925cd3 ("ALSA: pcm: Avoid potential races between OSS ioctls and read/write") Reported-by: syzbot+150189c103427d31a053@syzkaller.appspotmail.com Reported-by: syzbot+7e3f31a52646f939c052@syzkaller.appspotmail.com Reported-by: syzbot+4f2016cf5185da7759dc@syzkaller.appspotmail.com Cc: stable@vger.kernel.org Signed-off-by: Takashi Iwai tiwai@suse.de
diff --git a/sound/core/oss/pcm_oss.c b/sound/core/oss/pcm_oss.c index 481ab0e94ffa..1980f68246cb 100644 --- a/sound/core/oss/pcm_oss.c +++ b/sound/core/oss/pcm_oss.c @@ -1128,13 +1128,14 @@ static int snd_pcm_oss_get_active_substream(struct snd_pcm_oss_file *pcm_oss_fil }
/* call with params_lock held */ +/* NOTE: this always call PREPARE unconditionally no matter whether + * runtime->oss.prepare is set or not + */ static int snd_pcm_oss_prepare(struct snd_pcm_substream *substream) { int err; struct snd_pcm_runtime *runtime = substream->runtime;
- if (!runtime->oss.prepare) - return 0; err = snd_pcm_kernel_ioctl(substream, SNDRV_PCM_IOCTL_PREPARE, NULL); if (err < 0) { pcm_dbg(substream->pcm,