From: Takashi Iwai tiwai@suse.de
commit 8423f0b6d513b259fdab9c9bf4aaa6188d054c2d upstream.
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=WeLt57aaZ... Link: https://lore.kernel.org/r/20220905060714.22549-1-tiwai@suse.de Signed-off-by: Takashi Iwai tiwai@suse.de Signed-off-by: Zubin Mithra zsm@google.com --- Note: * 8423f0b6d513 is present in linux-5.15.y and linux-5.4.y; missing in linux-5.10.y. * Backport addresses conflict due to surrounding context. * Tests run: build and boot.
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 f88de74da1eb..de6f94bee50b 100644 --- a/sound/core/oss/pcm_oss.c +++ b/sound/core/oss/pcm_oss.c @@ -1662,13 +1662,14 @@ 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) {