ALSA: pcm: oss: Avoid plugin buffer overflow

commit f2ecf903ef06eb1bbbfa969db9889643d487e73a upstream.

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/sound/core/oss/pcm_plugin.c b/sound/core/oss/pcm_plugin.c
index c6888d76ca5e98734d1fe9bfa10b3e85d2de328c..b08b2d2d804bdb9d269e58f23c2889e3e1e26435 100644 (file)
--- a/sound/core/oss/pcm_plugin.c
+++ b/sound/core/oss/pcm_plugin.c
@@ -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);