Re: [PATCH -next] ALSA: Fix oversized kvmalloc() calls

[Takashi Iwai <tiwai@suse.de>]

On Tue, 30 Nov 2021 12:39:27 +0100,
Takashi Iwai wrote:
> 
> On Tue, 30 Nov 2021 12:16:18 +0100,
> Bixuan Cui wrote:
> > 
> > The commit 7661809d493b ("mm: don't allow oversized kvmalloc()
> > calls") limits the max allocatable memory via kvzalloc() to MAX_INT.
> > 
> > Reported-by: syzbot+bb348e9f9a954d42746f@syzkaller.appspotmail.com
> > Signed-off-by: Bixuan Cui <cuibixuan@linux.alibaba.com>
> 
> We should check the allocation size a lot earlier than here.
> IOW, such a big size shouldn't have been passed to this function but
> it should have been handled as an error in the caller side
> (snd_pcm_oss_change_params*()).
> 
> Could you give the reproducer?

I'm asking it because the patch like below might cover the case.


Takashi

-- 8< --
From: Takashi Iwai <tiwai@suse.de>
Subject: [PATCH] ALSA: pcm: oss: Fix negative period/buffer sizes

The period size calculation in OSS layer may receive a negative value
as an error, but the code there assumes only the positive values and
handle them with size_t.  Due to that, a too big value may be passed
to the lower layers.

This patch changes the code to handle with ssize_t and adds the proper
error checks appropriately.

Signed-off-by: Takashi Iwai <tiwai@suse.de>
---
 sound/core/oss/pcm_oss.c | 24 +++++++++++++++---------
 1 file changed, 15 insertions(+), 9 deletions(-)

diff --git a/sound/core/oss/pcm_oss.c b/sound/core/oss/pcm_oss.c
index 82a818734a5f..bec7590bc84b 100644
--- a/sound/core/oss/pcm_oss.c
+++ b/sound/core/oss/pcm_oss.c
@@ -147,7 +147,7 @@ snd_pcm_hw_param_value_min(const struct snd_pcm_hw_params *params,
  *
  * Return the maximum value for field PAR.
  */
-static unsigned int
+static int
 snd_pcm_hw_param_value_max(const struct snd_pcm_hw_params *params,
 			   snd_pcm_hw_param_t var, int *dir)
 {
@@ -682,18 +682,24 @@ static int snd_pcm_oss_period_size(struct snd_pcm_substream *substream,
 				   struct snd_pcm_hw_params *oss_params,
 				   struct snd_pcm_hw_params *slave_params)
 {
-	size_t s;
-	size_t oss_buffer_size, oss_period_size, oss_periods;
-	size_t min_period_size, max_period_size;
+	ssize_t s;
+	ssize_t oss_buffer_size;
+	ssize_t oss_period_size, oss_periods;
+	ssize_t min_period_size, max_period_size;
 	struct snd_pcm_runtime *runtime = substream->runtime;
 	size_t oss_frame_size;
 
 	oss_frame_size = snd_pcm_format_physical_width(params_format(oss_params)) *
 			 params_channels(oss_params) / 8;
 
+	oss_buffer_size = snd_pcm_hw_param_value_max(slave_params,
+						     SNDRV_PCM_HW_PARAM_BUFFER_SIZE,
+						     NULL);
+	if (oss_buffer_size <= 0)
+		return -EINVAL;
 	oss_buffer_size = snd_pcm_plug_client_size(substream,
-						   snd_pcm_hw_param_value_max(slave_params, SNDRV_PCM_HW_PARAM_BUFFER_SIZE, NULL)) * oss_frame_size;
-	if (!oss_buffer_size)
+						   oss_buffer_size * oss_frame_size);
+	if (oss_buffer_size <= 0)
 		return -EINVAL;
 	oss_buffer_size = rounddown_pow_of_two(oss_buffer_size);
 	if (atomic_read(&substream->mmap_count)) {
@@ -730,7 +736,7 @@ static int snd_pcm_oss_period_size(struct snd_pcm_substream *substream,
 
 	min_period_size = snd_pcm_plug_client_size(substream,
 						   snd_pcm_hw_param_value_min(slave_params, SNDRV_PCM_HW_PARAM_PERIOD_SIZE, NULL));
-	if (min_period_size) {
+	if (min_period_size > 0) {
 		min_period_size *= oss_frame_size;
 		min_period_size = roundup_pow_of_two(min_period_size);
 		if (oss_period_size < min_period_size)
@@ -739,7 +745,7 @@ static int snd_pcm_oss_period_size(struct snd_pcm_substream *substream,
 
 	max_period_size = snd_pcm_plug_client_size(substream,
 						   snd_pcm_hw_param_value_max(slave_params, SNDRV_PCM_HW_PARAM_PERIOD_SIZE, NULL));
-	if (max_period_size) {
+	if (max_period_size > 0) {
 		max_period_size *= oss_frame_size;
 		max_period_size = rounddown_pow_of_two(max_period_size);
 		if (oss_period_size > max_period_size)
@@ -752,7 +758,7 @@ static int snd_pcm_oss_period_size(struct snd_pcm_substream *substream,
 		oss_periods = substream->oss.setup.periods;
 
 	s = snd_pcm_hw_param_value_max(slave_params, SNDRV_PCM_HW_PARAM_PERIODS, NULL);
-	if (runtime->oss.maxfrags && s > runtime->oss.maxfrags)
+	if (s > 0 && runtime->oss.maxfrags && s > runtime->oss.maxfrags)
 		s = runtime->oss.maxfrags;
 	if (oss_periods > s)
 		oss_periods = s;
-- 
2.31.1