[alsa-devel] [PATCH] ALSA: pcm: oss: Avoid potential buffer overflows

[Takashi Iwai]

syzkaller reported an invalid access in PCM OSS read, and this seems
to be an overflow of the internal buffer allocated for a plugin.
Since the rate plugin adjusts its transfer size dynamically, the
calculation for the chained plugin might be bigger than the given
buffer size in some extreme cases, which lead to such an buffer
overflow as caught by KASAN.

Fix it by limiting the max transfer size properly by checking against
the destination size in each plugin transfer callback.

Reported-by: syzbot+f153bde47a62e0b05f83 at syzkaller.appspotmail.com
Cc: <stable at vger.kernel.org>
Signed-off-by: Takashi Iwai <tiwai at suse.de>
---
 sound/core/oss/linear.c | 2 ++
 sound/core/oss/mulaw.c  | 2 ++
 sound/core/oss/route.c  | 2 ++
 3 files changed, 6 insertions(+)

diff --git a/sound/core/oss/linear.c b/sound/core/oss/linear.c
index 2045697f449d..797d838a2f9e 100644
--- a/sound/core/oss/linear.c
+++ b/sound/core/oss/linear.c
@@ -107,6 +107,8 @@ static snd_pcm_sframes_t linear_transfer(struct snd_pcm_plugin *plugin,
 		}
 	}
 #endif
+	if (frames > dst_channels[0].frames)
+		frames = dst_channels[0].frames;
 	convert(plugin, src_channels, dst_channels, frames);
 	return frames;
 }
diff --git a/sound/core/oss/mulaw.c b/sound/core/oss/mulaw.c
index 7915564bd394..3788906421a7 100644
--- a/sound/core/oss/mulaw.c
+++ b/sound/core/oss/mulaw.c
@@ -269,6 +269,8 @@ static snd_pcm_sframes_t mulaw_transfer(struct snd_pcm_plugin *plugin,
 		}
 	}
 #endif
+	if (frames > dst_channels[0].frames)
+		frames = dst_channels[0].frames;
 	data = (struct mulaw_priv *)plugin->extra_data;
 	data->func(plugin, src_channels, dst_channels, frames);
 	return frames;
diff --git a/sound/core/oss/route.c b/sound/core/oss/route.c
index c8171f5783c8..72dea04197ef 100644
--- a/sound/core/oss/route.c
+++ b/sound/core/oss/route.c
@@ -57,6 +57,8 @@ static snd_pcm_sframes_t route_transfer(struct snd_pcm_plugin *plugin,
 		return -ENXIO;
 	if (frames == 0)
 		return 0;
+	if (frames > dst_channels[0].frames)
+		frames = dst_channels[0].frames;
 
 	nsrcs = plugin->src_format.channels;
 	ndsts = plugin->dst_format.channels;
-- 
2.16.4