6.6-stable review patch. If anyone has any objections, please let me know.
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From: Takashi Iwai tiwai@suse.de
commit 93a81ca0657758b607c3f4ba889ae806be9beb73 upstream.
The PCM OSS layer tries to clear the buffer with the silence data at initialization (or reconfiguration) of a stream with the explicit call of snd_pcm_format_set_silence() with runtime->dma_area. But this may lead to a UAF because the accessed runtime->dma_area might be freed concurrently, as it's performed outside the PCM ops.
For avoiding it, move the code into the PCM core and perform it inside the buffer access lock, so that it won't be changed during the operation.
Reported-by: syzbot+32d4647f551007595173@syzkaller.appspotmail.com Closes: https://lore.kernel.org/68164d8e.050a0220.11da1b.0019.GAE@google.com Cc: stable@vger.kernel.org Link: https://patch.msgid.link/20250516080817.20068-1-tiwai@suse.de Signed-off-by: Takashi Iwai tiwai@suse.de Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- include/sound/pcm.h | 2 ++ sound/core/oss/pcm_oss.c | 3 +-- sound/core/pcm_native.c | 11 +++++++++++ 3 files changed, 14 insertions(+), 2 deletions(-)
--- a/include/sound/pcm.h +++ b/include/sound/pcm.h @@ -1427,6 +1427,8 @@ int snd_pcm_lib_mmap_iomem(struct snd_pc #define snd_pcm_lib_mmap_iomem NULL #endif
+void snd_pcm_runtime_buffer_set_silence(struct snd_pcm_runtime *runtime); + /** * snd_pcm_limit_isa_dma_size - Get the max size fitting with ISA DMA transfer * @dma: DMA number --- a/sound/core/oss/pcm_oss.c +++ b/sound/core/oss/pcm_oss.c @@ -1085,8 +1085,7 @@ static int snd_pcm_oss_change_params_loc runtime->oss.params = 0; runtime->oss.prepare = 1; runtime->oss.buffer_used = 0; - if (runtime->dma_area) - snd_pcm_format_set_silence(runtime->format, runtime->dma_area, bytes_to_samples(runtime, runtime->dma_bytes)); + snd_pcm_runtime_buffer_set_silence(runtime);
runtime->oss.period_frames = snd_pcm_alsa_frames(substream, oss_period_size);
--- a/sound/core/pcm_native.c +++ b/sound/core/pcm_native.c @@ -703,6 +703,17 @@ static void snd_pcm_buffer_access_unlock atomic_inc(&runtime->buffer_accessing); }
+/* fill the PCM buffer with the current silence format; called from pcm_oss.c */ +void snd_pcm_runtime_buffer_set_silence(struct snd_pcm_runtime *runtime) +{ + snd_pcm_buffer_access_lock(runtime); + if (runtime->dma_area) + snd_pcm_format_set_silence(runtime->format, runtime->dma_area, + bytes_to_samples(runtime, runtime->dma_bytes)); + snd_pcm_buffer_access_unlock(runtime); +} +EXPORT_SYMBOL_GPL(snd_pcm_runtime_buffer_set_silence); + #if IS_ENABLED(CONFIG_SND_PCM_OSS) #define is_oss_stream(substream) ((substream)->oss.oss) #else