ALSA: pcm: oss: Avoid plugin buffer overflow (f2ecf903) · Commits · 戴 / test

Each OSS PCM plugins allocate its internal buffer per pre-calculation of the max buffer size through the chain of plugins (calling src_frames and dst_frames callbacks). This works for most plugins, but the rate plugin might behave incorrectly. The calculation in the rate plugin involves with the fractional position, i.e. it may vary depending on the input position. Since the buffer size pre-calculation is always done with the offset zero, it may return a shorter size than it might be; this may result in the out-of-bound access as spotted by fuzzer. This patch addresses those possible buffer overflow accesses by simply setting the upper limit per the given buffer size for each plugin before src_frames() and after dst_frames() calls. Reported-by:

<syzbot+e1fe9f44fb8ecf4fb5dd@syzkaller.appspotmail.com> Cc: <stable@vger.kernel.org> Link: https://lore.kernel.org/r/000000000000b25ea005a02bcf21@google.com Link: https://lore.kernel.org/r/20200309082148.19855-1-tiwai@suse.de Signed-off-by:

Takashi Iwai <tiwai@suse.de>

sound/core/oss/pcm_plugin.c

+8 −0

Original line number	Diff line number	Diff line
		@@ -209,6 +209,8 @@ snd_pcm_sframes_t snd_pcm_plug_client_size(struct snd_pcm_substream *plug, snd_p
		if (stream == SNDRV_PCM_STREAM_PLAYBACK) {
		plugin = snd_pcm_plug_last(plug);
		while (plugin && drv_frames > 0) {
		if (drv_frames > plugin->buf_frames)
		drv_frames = plugin->buf_frames;
		plugin_prev = plugin->prev;
		if (plugin->src_frames)
		drv_frames = plugin->src_frames(plugin, drv_frames);
		@@ -220,6 +222,8 @@ snd_pcm_sframes_t snd_pcm_plug_client_size(struct snd_pcm_substream *plug, snd_p
		plugin_next = plugin->next;
		if (plugin->dst_frames)
		drv_frames = plugin->dst_frames(plugin, drv_frames);
		if (drv_frames > plugin->buf_frames)
		drv_frames = plugin->buf_frames;
		plugin = plugin_next;
		}
		} else
		@@ -248,11 +252,15 @@ snd_pcm_sframes_t snd_pcm_plug_slave_size(struct snd_pcm_substream *plug, snd_pc
		if (frames < 0)
		return frames;
		}
		if (frames > plugin->buf_frames)
		frames = plugin->buf_frames;
		plugin = plugin_next;
		}
		} else if (stream == SNDRV_PCM_STREAM_CAPTURE) {
		plugin = snd_pcm_plug_last(plug);
		while (plugin) {
		if (frames > plugin->buf_frames)
		frames = plugin->buf_frames;
		plugin_prev = plugin->prev;
		if (plugin->src_frames) {
		frames = plugin->src_frames(plugin, frames);

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