[PATCH] ALSA: oss: Fix PCM OSS buffer allocation overflow

[Takashi Iwai <tiwai@suse.de>]

We've got syzbot reports hitting INT_MAX overflow at vmalloc()
allocation that is called from snd_pcm_plug_alloc().  Although we
apply the restrictions to input parameters, it's based only on the
hw_params of the underlying PCM device.  Since the PCM OSS layer
allocates a temporary buffer for the data conversion, the size may
become unexpectedly large when more channels or higher rates is given;
in the reported case, it went over INT_MAX, hence it hits WARN_ON().

This patch is an attempt to avoid such an overflow and an allocation
for too large buffers.  First off, it adds the limit of 1MB as the
upper bound for period bytes.  This must be large enough for all use
cases, and we really don't want to handle a larger temporary buffer
than this size.  The size check is performed at two places, where the
original period bytes is calculated and where the plugin buffer size
is calculated.

In addition, the driver uses array_size() and array3_size() for
multiplications to catch overflows for the converted period size and
buffer bytes.

Reported-by: syzbot+72732c532ac1454eeee9@syzkaller.appspotmail.com
Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Cc: <stable@vger.kernel.org>
Link: https://lore.kernel.org/r/00000000000085b1b305da5a66f3@google.com
Signed-off-by: Takashi Iwai <tiwai@suse.de>
---
 sound/core/oss/pcm_oss.c    | 12 ++++++++----
 sound/core/oss/pcm_plugin.c |  5 ++++-
 2 files changed, 12 insertions(+), 5 deletions(-)

diff --git a/sound/core/oss/pcm_oss.c b/sound/core/oss/pcm_oss.c
index 3ee9edf85815..f158f0abd25d 100644
--- a/sound/core/oss/pcm_oss.c
+++ b/sound/core/oss/pcm_oss.c
@@ -774,6 +774,11 @@ static int snd_pcm_oss_period_size(struct snd_pcm_substream *substream,
 
 	if (oss_period_size < 16)
 		return -EINVAL;
+
+	/* don't allocate too large period; 1MB period must be enough */
+	if (oss_period_size > 1024 * 1024)
+		return -ENOMEM;
+
 	runtime->oss.period_bytes = oss_period_size;
 	runtime->oss.period_frames = 1;
 	runtime->oss.periods = oss_periods;
@@ -1043,10 +1048,9 @@ static int snd_pcm_oss_change_params_locked(struct snd_pcm_substream *substream)
 			goto failure;
 	}
 #endif
-	oss_period_size *= oss_frame_size;
-
-	oss_buffer_size = oss_period_size * runtime->oss.periods;
-	if (oss_buffer_size < 0) {
+	oss_period_size = array_size(oss_period_size, oss_frame_size);
+	oss_buffer_size = array_size(oss_period_size, runtime->oss.periods);
+	if (oss_buffer_size <= 0) {
 		err = -EINVAL;
 		goto failure;
 	}
diff --git a/sound/core/oss/pcm_plugin.c b/sound/core/oss/pcm_plugin.c
index 061ba06bc926..82e180c776ae 100644
--- a/sound/core/oss/pcm_plugin.c
+++ b/sound/core/oss/pcm_plugin.c
@@ -62,7 +62,10 @@ static int snd_pcm_plugin_alloc(struct snd_pcm_plugin *plugin, snd_pcm_uframes_t
 	width = snd_pcm_format_physical_width(format->format);
 	if (width < 0)
 		return width;
-	size = frames * format->channels * width;
+	size = array3_size(frames, format->channels, width);
+	/* check for too large period size once again */
+	if (size > 1024 * 1024)
+		return -ENOMEM;
 	if (snd_BUG_ON(size % 8))
 		return -ENXIO;
 	size /= 8;
-- 
2.34.1