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 5de4bd872fa805b68160a837a0a588f015361c76..fa23192689247389d43027e13d7f4c4d22536bfb 100644 (file)
--- a/include/sound/pcm.h
+++ b/include/sound/pcm.h
@@ -1384,6 +1384,8 @@ 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 8a458c167452a7c306a59b531adccb0b03e9260e..a2b9d1f0b0722b55b308488fd25eda5a477373eb 100644 (file)
--- a/sound/core/oss/pcm_oss.c
+++ b/sound/core/oss/pcm_oss.c
@@ -1079,8 +1079,7 @@ 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 56b4a25fc6f0b96f3684fdace6e00bd4b79fcddd..d6169fee5ea0b335c6d498898ca905fdcb1dd33f 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