[PATCH 4.9 016/102] ALSA: pcm: oss: Avoid plugin buffer overflow

[Greg Kroah-Hartman]

From: Takashi Iwai <tiwai@xxxxxxx>

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@xxxxxxxxxxxxxxxxxxxxxxxxx
Cc: <stable@xxxxxxxxxxxxxxx>
Link: https://lore.kernel.org/r/000000000000b25ea005a02bcf21@xxxxxxxxxx
Link: https://lore.kernel.org/r/20200309082148.19855-1-tiwai@xxxxxxx
Signed-off-by: Takashi Iwai <tiwai@xxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 sound/core/oss/pcm_plugin.c |    8 ++++++++
 1 file changed, 8 insertions(+)

--- 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_si
 	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_si
 			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_siz
 				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);