[PATCH] ALSA: pcm: Fix snd_pcm_hw_params struct copy in compat mode

[PATCH] ALSA: pcm: Fix snd_pcm_hw_params struct copy in compat mode

[Nicolas Boichat]

Running a kernel with KASan enabled, we spotted that the following
read in sound/soc/soc-pcm.c:soc_pcm_hw_params() is out of bounds:

		/* copy params for each codec */
		codec_params = *params;

The problem comes from sound/core/pcm_compat.c,
snd_pcm_ioctl_hw_params_compat, where we're copying from a
struct snd_pcm_hw_params to a struct snd_pcm_hw_params32:

	/* only fifo_size is different, so just copy all */
	data = memdup_user(data32, sizeof(*data32));

It turns out that snd_pcm_hw_params is 4 bytes longer than
snd_pcm_hw_params32, that's why an out-of-bounds read happens.

We separate kmalloc and memory copy operations to make sure
data has the correct length.

Signed-off-by: Nicolas Boichat <drinkcat@chromium.org>
---
 sound/core/pcm_compat.c | 13 +++++++++----
 1 file changed, 9 insertions(+), 4 deletions(-)

diff --git a/sound/core/pcm_compat.c b/sound/core/pcm_compat.c
index b48b434..9630e9f 100644
--- a/sound/core/pcm_compat.c
+++ b/sound/core/pcm_compat.c
@@ -255,10 +255,15 @@ static int snd_pcm_ioctl_hw_params_compat(struct snd_pcm_substream *substream,
 	if (! (runtime = substream->runtime))
 		return -ENOTTY;
 
-	/* only fifo_size is different, so just copy all */
-	data = memdup_user(data32, sizeof(*data32));
-	if (IS_ERR(data))
-		return PTR_ERR(data);
+	data = kmalloc(sizeof(*data), GFP_KERNEL);
+	if (!data)
+		return -ENOMEM;
+
+	/* only fifo_size (RO from userspace) is different, so just copy all */
+	if (copy_from_user(data, data32, sizeof(*data32))) {
+		err = -EFAULT;
+		goto error;
+	}
 
 	if (refine)
 		err = snd_pcm_hw_refine(substream, data);
-- 
2.6.0.rc2.230.g3dd15c0

Re: [PATCH] ALSA: pcm: Fix snd_pcm_hw_params struct copy in compat mode

[Takashi Iwai]

On Mon, 18 Jan 2016 04:49:18 +0100,
Nicolas Boichat wrote:
> 
> Running a kernel with KASan enabled, we spotted that the following
> read in sound/soc/soc-pcm.c:soc_pcm_hw_params() is out of bounds:
> 
> 		/* copy params for each codec */
> 		codec_params = *params;
> 
> The problem comes from sound/core/pcm_compat.c,
> snd_pcm_ioctl_hw_params_compat, where we're copying from a
> struct snd_pcm_hw_params to a struct snd_pcm_hw_params32:
> 
> 	/* only fifo_size is different, so just copy all */
> 	data = memdup_user(data32, sizeof(*data32));
> 
> It turns out that snd_pcm_hw_params is 4 bytes longer than
> snd_pcm_hw_params32, that's why an out-of-bounds read happens.
> 
> We separate kmalloc and memory copy operations to make sure
> data has the correct length.
> 
> Signed-off-by: Nicolas Boichat <drinkcat@chromium.org>

Thanks for reporting.  This is indeed effectively a revert of the
commit ef44a1ec6eee ('ALSA: sound/core: use memdup_user()'), which is
obviously wrong.  Sigh, it's a really danger of such a "cleanup"
patch.
    
Could you rephrase the changelog mentioning the affecting commit and
resubmit?


Takashi

> ---
>  sound/core/pcm_compat.c | 13 +++++++++----
>  1 file changed, 9 insertions(+), 4 deletions(-)
> 
> diff --git a/sound/core/pcm_compat.c b/sound/core/pcm_compat.c
> index b48b434..9630e9f 100644
> --- a/sound/core/pcm_compat.c
> +++ b/sound/core/pcm_compat.c
> @@ -255,10 +255,15 @@ static int snd_pcm_ioctl_hw_params_compat(struct snd_pcm_substream *substream,
>  	if (! (runtime = substream->runtime))
>  		return -ENOTTY;
>  
> -	/* only fifo_size is different, so just copy all */
> -	data = memdup_user(data32, sizeof(*data32));
> -	if (IS_ERR(data))
> -		return PTR_ERR(data);
> +	data = kmalloc(sizeof(*data), GFP_KERNEL);
> +	if (!data)
> +		return -ENOMEM;
> +
> +	/* only fifo_size (RO from userspace) is different, so just copy all */
> +	if (copy_from_user(data, data32, sizeof(*data32))) {
> +		err = -EFAULT;
> +		goto error;
> +	}
>  
>  	if (refine)
>  		err = snd_pcm_hw_refine(substream, data);
> -- 
> 2.6.0.rc2.230.g3dd15c0
> 
> 

Re: [PATCH] ALSA: pcm: Fix snd_pcm_hw_params struct copy in compat mode

[Nicolas Boichat]

On Mon, Jan 18, 2016 at 2:37 PM, Takashi Iwai <tiwai@suse.de> wrote:
> On Mon, 18 Jan 2016 04:49:18 +0100,
> Nicolas Boichat wrote:
>>
>> Running a kernel with KASan enabled, we spotted that the following
>> read in sound/soc/soc-pcm.c:soc_pcm_hw_params() is out of bounds:
>>
>>               /* copy params for each codec */
>>               codec_params = *params;
>>
>> The problem comes from sound/core/pcm_compat.c,
>> snd_pcm_ioctl_hw_params_compat, where we're copying from a
>> struct snd_pcm_hw_params to a struct snd_pcm_hw_params32:
>>
>>       /* only fifo_size is different, so just copy all */
>>       data = memdup_user(data32, sizeof(*data32));
>>
>> It turns out that snd_pcm_hw_params is 4 bytes longer than
>> snd_pcm_hw_params32, that's why an out-of-bounds read happens.
>>
>> We separate kmalloc and memory copy operations to make sure
>> data has the correct length.
>>
>> Signed-off-by: Nicolas Boichat <drinkcat@chromium.org>
>
> Thanks for reporting.  This is indeed effectively a revert of the
> commit ef44a1ec6eee ('ALSA: sound/core: use memdup_user()'), which is
> obviously wrong.  Sigh, it's a really danger of such a "cleanup"
> patch.

Oh, well spotted!

> Could you rephrase the changelog mentioning the affecting commit and
> resubmit?

Sure. Looking at that commit, there is another suspicious memdup_user
in sound/seq/seq_compat.c (similar issue: struct snd_seq_port_info32
is 4 bytes shorter than struct snd_seq_port_info). I'll revert that
one as well.

>
> Takashi
>
>> ---
>>  sound/core/pcm_compat.c | 13 +++++++++----
>>  1 file changed, 9 insertions(+), 4 deletions(-)
>>
>> diff --git a/sound/core/pcm_compat.c b/sound/core/pcm_compat.c
>> index b48b434..9630e9f 100644
>> --- a/sound/core/pcm_compat.c
>> +++ b/sound/core/pcm_compat.c
>> @@ -255,10 +255,15 @@ static int snd_pcm_ioctl_hw_params_compat(struct snd_pcm_substream *substream,
>>       if (! (runtime = substream->runtime))
>>               return -ENOTTY;
>>
>> -     /* only fifo_size is different, so just copy all */
>> -     data = memdup_user(data32, sizeof(*data32));
>> -     if (IS_ERR(data))
>> -             return PTR_ERR(data);
>> +     data = kmalloc(sizeof(*data), GFP_KERNEL);
>> +     if (!data)
>> +             return -ENOMEM;
>> +
>> +     /* only fifo_size (RO from userspace) is different, so just copy all */
>> +     if (copy_from_user(data, data32, sizeof(*data32))) {
>> +             err = -EFAULT;
>> +             goto error;
>> +     }
>>
>>       if (refine)
>>               err = snd_pcm_hw_refine(substream, data);
>> --
>> 2.6.0.rc2.230.g3dd15c0
>>
>>

Re: [PATCH] ALSA: pcm: Fix snd_pcm_hw_params struct copy in compat mode

[Takashi Iwai]

On Mon, 18 Jan 2016 14:00:19 +0100,
Nicolas Boichat wrote:
> 
> On Mon, Jan 18, 2016 at 2:37 PM, Takashi Iwai <tiwai@suse.de> wrote:
> > On Mon, 18 Jan 2016 04:49:18 +0100,
> > Nicolas Boichat wrote:
> >>
> >> Running a kernel with KASan enabled, we spotted that the following
> >> read in sound/soc/soc-pcm.c:soc_pcm_hw_params() is out of bounds:
> >>
> >>               /* copy params for each codec */
> >>               codec_params = *params;
> >>
> >> The problem comes from sound/core/pcm_compat.c,
> >> snd_pcm_ioctl_hw_params_compat, where we're copying from a
> >> struct snd_pcm_hw_params to a struct snd_pcm_hw_params32:
> >>
> >>       /* only fifo_size is different, so just copy all */
> >>       data = memdup_user(data32, sizeof(*data32));
> >>
> >> It turns out that snd_pcm_hw_params is 4 bytes longer than
> >> snd_pcm_hw_params32, that's why an out-of-bounds read happens.
> >>
> >> We separate kmalloc and memory copy operations to make sure
> >> data has the correct length.
> >>
> >> Signed-off-by: Nicolas Boichat <drinkcat@chromium.org>
> >
> > Thanks for reporting.  This is indeed effectively a revert of the
> > commit ef44a1ec6eee ('ALSA: sound/core: use memdup_user()'), which is
> > obviously wrong.  Sigh, it's a really danger of such a "cleanup"
> > patch.
> 
> Oh, well spotted!
> 
> > Could you rephrase the changelog mentioning the affecting commit and
> > resubmit?
> 
> Sure. Looking at that commit, there is another suspicious memdup_user
> in sound/seq/seq_compat.c (similar issue: struct snd_seq_port_info32
> is 4 bytes shorter than struct snd_seq_port_info). I'll revert that
> one as well.

Good catch.  I'm looking forward to seeing newer patches!


Takashi