[SRU Bionic 1/1] ALSA: pcm: oss: Fix race at SNDCTL_DSP_SYNC

[Cengiz Can]

From: Sasha Levin <sashal at kernel.org>

[ Upstream commit 8423f0b6d513b259fdab9c9bf4aaa6188d054c2d ]

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 at gmail.com>
Reviewed-by: Jaroslav Kysela <perex at perex.cz>
Cc: <stable at 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 at suse.de>
Signed-off-by: Sasha Levin <sashal at kernel.org>
CVE-2022-3303
(cherry picked from commit 4051324a6dafd7053c74c475e80b3ba10ae672b0 linux-5.4.y)
Signed-off-by: Cengiz Can <cengiz.can at canonical.com>
---
 sound/core/oss/pcm_oss.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/sound/core/oss/pcm_oss.c b/sound/core/oss/pcm_oss.c
index 87806dab321a..2bc560787ef6 100644
--- a/sound/core/oss/pcm_oss.c
+++ b/sound/core/oss/pcm_oss.c
@@ -1672,13 +1672,14 @@ static int snd_pcm_oss_sync(struct snd_pcm_oss_file *pcm_oss_file)
 		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) {
-- 
2.39.2