From 8423f0b6d513b259fdab9c9bf4aaa6188d054c2d Mon Sep 17 00:00:00 2001

From: Takashi Iwai <tiwai@suse.de>

Date: Mon, 5 Sep 2022 08:07:14 +0200

Subject: [PATCH] ALSA: pcm: oss: Fix race at SNDCTL_DSP_SYNC

Git-commit: 8423f0b6d513b259fdab9c9bf4aaa6188d054c2d

Patch-mainline: v6.0-rc5

References: CVE-2022-3303 bsc#1203769

There is a small race window at snd_pcm_oss_sync() that is called from

OSS PCM SNDCTL_DSP_SYNC ioctl; namely the function calls

snd_pcm_oss_make_ready() at first, then takes the params_lock mutex

for the rest.  When the stream is set up again by another thread

between them, it leads to inconsistency, and may result in unexpected

results such as NULL dereference of OSS buffer as a fuzzer spotted

recently.

The fix is simply to cover snd_pcm_oss_make_ready() call into the same

params_lock mutex with snd_pcm_oss_make_ready_locked() variant.

Reported-and-tested-by: butt3rflyh4ck <butterflyhuangxx@gmail.com>

Reviewed-by: Jaroslav Kysela <perex@perex.cz>

Cc: <stable@vger.kernel.org>

Link: https://lore.kernel.org/r/CAFcO6XN7JDM4xSXGhtusQfS2mSBcx50VJKwQpCq=WeLt57aaZA@mail.gmail.com

Link: https://lore.kernel.org/r/20220905060714.22549-1-tiwai@suse.de

Signed-off-by: Takashi Iwai <tiwai@suse.de>

---

 sound/core/oss/pcm_oss.c |    5 +++--

 1 file changed, 3 insertions(+), 2 deletions(-)

--- a/sound/core/oss/pcm_oss.c

+++ b/sound/core/oss/pcm_oss.c

@@ -1645,13 +1645,14 @@ static int snd_pcm_oss_sync(struct snd_p

 		runtime = substream->runtime;

 		if (atomic_read(&substream->mmap_count))

 			goto __direct;

-		if ((err = snd_pcm_oss_make_ready(substream)) < 0)

-			return err;

 		atomic_inc(&runtime->oss.rw_ref);

 		if (mutex_lock_interruptible(&runtime->oss.params_lock)) {

 			atomic_dec(&runtime->oss.rw_ref);

 			return -ERESTARTSYS;

 		}

+		err = snd_pcm_oss_make_ready_locked(substream);

+		if (err < 0)

+			goto unlock;

 		format = snd_pcm_oss_format_from(runtime->oss.format);

 		width = snd_pcm_format_physical_width(format);

 		if (runtime->oss.buffer_used > 0) {