ALSA: pcm: oss: Fix race at SNDCTL_DSP_SYNC

[ Upstream commit f54c529a5c66d329621e8718c2773a3baa5f4759 ]

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>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/sound/core/oss/pcm_oss.c b/sound/core/oss/pcm_oss.c
index ad4e0af2d0d0361414e971564515b7e8a59e2891..51d2911366e9308cc64a7103be30186b64628956 100644 (file)
--- a/sound/core/oss/pcm_oss.c
+++ b/sound/core/oss/pcm_oss.c
@@ -1661,13 +1661,14 @@ 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) {