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

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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>
This commit is contained in:
Takashi Iwai
2025-05-16 10:08:16 +02:00
committed by Greg Kroah-Hartman
parent b5bada85c1
commit 74d90875f3
3 changed files with 14 additions and 2 deletions
Download Patch File Download Diff File Expand all files Collapse all files

2
include/sound/pcm.h
View File

@@ -1427,6 +1427,8 @@ int snd_pcm_lib_mmap_iomem(struct snd_pcm_substream *substream, struct vm_area_s
#define snd_pcm_lib_mmap_iomem NULL #define snd_pcm_lib_mmap_iomem NULL
#endif #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 * snd_pcm_limit_isa_dma_size - Get the max size fitting with ISA DMA transfer
* @dma: DMA number * @dma: DMA number

3
sound/core/oss/pcm_oss.c
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@@ -1085,8 +1085,7 @@ static int snd_pcm_oss_change_params_locked(struct snd_pcm_substream *substream)
runtime->oss.params = 0; runtime->oss.params = 0;
runtime->oss.prepare = 1; runtime->oss.prepare = 1;
runtime->oss.buffer_used = 0; runtime->oss.buffer_used = 0;
if (runtime->dma_area) snd_pcm_runtime_buffer_set_silence(runtime);
snd_pcm_format_set_silence(runtime->format, runtime->dma_area, bytes_to_samples(runtime, runtime->dma_bytes));
runtime->oss.period_frames = snd_pcm_alsa_frames(substream, oss_period_size); runtime->oss.period_frames = snd_pcm_alsa_frames(substream, oss_period_size);

11
sound/core/pcm_native.c
View File

@@ -703,6 +703,17 @@ static void snd_pcm_buffer_access_unlock(struct snd_pcm_runtime *runtime)
atomic_inc(&runtime->buffer_accessing); 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) #if IS_ENABLED(CONFIG_SND_PCM_OSS)
#define is_oss_stream(substream) ((substream)->oss.oss) #define is_oss_stream(substream) ((substream)->oss.oss)
#else #else