ALSA: pcm: Fix race of buffer access at PCM OSS layer

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>

diff --git a/include/sound/pcm.h b/include/sound/pcm.h
index 27040b472a4f69dec49c3c2bf68e3f840b67d349..51881ffbd155f4d1d1d6c1516886eaf11ca75cf8 100644 (file)
--- a/include/sound/pcm.h
+++ b/include/sound/pcm.h
@@ -1429,6 +1429,8 @@ int snd_pcm_lib_mmap_iomem(struct snd_pcm_substream *substream, struct vm_area_s
 #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

diff --git a/sound/core/oss/pcm_oss.c b/sound/core/oss/pcm_oss.c
index ac2efeb63a39637d0399c3273491bb3924c9ddde..2b9fada9753227cfe8f3967ab0fad9b5d0b105b4 100644 (file)
--- 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_locked(struct snd_pcm_substream *substream)
        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);
 

diff --git a/sound/core/pcm_native.c b/sound/core/pcm_native.c
index f46b87ca76d0d842e0e35418f0d66ede1c2d4705..bf752b188b05614d2751cb4bfe990ac3be52900a 100644 (file)
--- a/sound/core/pcm_native.c
+++ b/sound/core/pcm_native.c
@@ -703,6 +703,17 @@ static void snd_pcm_buffer_access_unlock(struct snd_pcm_runtime *runtime)
        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