[1/1] v4l: ioctl: Fix memory leak in video_usercopy

When an IOCTL with argument size larger than 128 that also used array
arguments were handled, two memory allocations were made but alas, only
the latter one of them was released. This happened because there was only
a single local variable to hold such a temporary allocation.

Fix this by adding separate variables to hold the pointers to the
temporary allocations.

Reported-by: Arnd Bergmann <arnd@kernel.org>
Reported-by: syzbot+1115e79c8df6472c612b@syzkaller.appspotmail.com
Fixes: d14e6d76ebf7 ("[media] v4l: Add multi-planar ioctl handling code")
Cc: stable@vger.kernel.org
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
---
 drivers/media/v4l2-core/v4l2-ioctl.c | 31 +++++++++++++---------------
 1 file changed, 14 insertions(+), 17 deletions(-)

On Sun, Dec 20, 2020 at 12:06 PM Sakari Ailus
<sakari.ailus@linux.intel.com> wrote:
>
> When an IOCTL with argument size larger than 128 that also used array
> arguments were handled, two memory allocations were made but alas, only
> the latter one of them was released. This happened because there was only
> a single local variable to hold such a temporary allocation.
>
> Fix this by adding separate variables to hold the pointers to the
> temporary allocations.
>
> Reported-by: Arnd Bergmann <arnd@kernel.org>
> Reported-by: syzbot+1115e79c8df6472c612b@syzkaller.appspotmail.com
> Fixes: d14e6d76ebf7 ("[media] v4l: Add multi-planar ioctl handling code")
> Cc: stable@vger.kernel.org
> Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>

Acked-by: Arnd Bergmann <arnd@arndb.de>

>  out:
> +       kvfree(array_buf);
>         kvfree(mbuf);

I think it would make sense to change mbuf back to kzalloc()/kfree
after this, since the size of the ioctl argument has an upper bound
of 2^_IOC_SIZEBITS (16KB), which does not need the vmalloc
path, unlike the array args.

        Arnd

Hi Sakari,

Thank you for the patch.

On Sun, Dec 20, 2020 at 01:06:51PM +0200, Sakari Ailus wrote:
> When an IOCTL with argument size larger than 128 that also used array
> arguments were handled, two memory allocations were made but alas, only
> the latter one of them was released.

Alas, this fills my heart with sorrow indeed :-)

> This happened because there was only
> a single local variable to hold such a temporary allocation.
> 
> Fix this by adding separate variables to hold the pointers to the
> temporary allocations.
> 
> Reported-by: Arnd Bergmann <arnd@kernel.org>
> Reported-by: syzbot+1115e79c8df6472c612b@syzkaller.appspotmail.com
> Fixes: d14e6d76ebf7 ("[media] v4l: Add multi-planar ioctl handling code")
> Cc: stable@vger.kernel.org
> Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
> ---
>  drivers/media/v4l2-core/v4l2-ioctl.c | 31 +++++++++++++---------------
>  1 file changed, 14 insertions(+), 17 deletions(-)
> 
> diff --git a/drivers/media/v4l2-core/v4l2-ioctl.c b/drivers/media/v4l2-core/v4l2-ioctl.c
> index 3198abdd538ce..f42a779948779 100644
> --- a/drivers/media/v4l2-core/v4l2-ioctl.c
> +++ b/drivers/media/v4l2-core/v4l2-ioctl.c
> @@ -3283,7 +3283,7 @@ video_usercopy(struct file *file, unsigned int orig_cmd, unsigned long arg,
>  	       v4l2_kioctl func)
>  {
>  	char	sbuf[128];
> -	void    *mbuf = NULL;
> +	void    *mbuf = NULL, *array_buf = NULL;
>  	void	*parg = (void *)arg;
>  	long	err  = -EINVAL;
>  	bool	has_array_args;
> @@ -3318,27 +3318,21 @@ video_usercopy(struct file *file, unsigned int orig_cmd, unsigned long arg,
>  	has_array_args = err;
>  
>  	if (has_array_args) {
> -		/*
> -		 * When adding new types of array args, make sure that the
> -		 * parent argument to ioctl (which contains the pointer to the
> -		 * array) fits into sbuf (so that mbuf will still remain
> -		 * unused up to here).
> -		 */
> -		mbuf = kvmalloc(array_size, GFP_KERNEL);
> +		array_buf = kvmalloc(array_size, GFP_KERNEL);
>  		err = -ENOMEM;
> -		if (NULL == mbuf)
> +		if (array_buf == NULL)
>  			goto out_array_args;
>  		err = -EFAULT;
>  		if (in_compat_syscall())
> -			err = v4l2_compat_get_array_args(file, mbuf, user_ptr,
> -							 array_size, orig_cmd,
> -							 parg);
> +			err = v4l2_compat_get_array_args(file, array_buf,
> +							 user_ptr, array_size,
> +							 orig_cmd, parg);
>  		else
> -			err = copy_from_user(mbuf, user_ptr, array_size) ?
> +			err = copy_from_user(array_buf, user_ptr, array_size) ?
>  								-EFAULT : 0;
>  		if (err)
>  			goto out_array_args;
> -		*kernel_ptr = mbuf;
> +		*kernel_ptr = array_buf;
>  	}
>  
>  	/* Handles IOCTL */
> @@ -3360,12 +3354,14 @@ video_usercopy(struct file *file, unsigned int orig_cmd, unsigned long arg,
>  		if (in_compat_syscall()) {
>  			int put_err;
>  
> -			put_err = v4l2_compat_put_array_args(file, user_ptr, mbuf,
> -							     array_size, orig_cmd,
> +			put_err = v4l2_compat_put_array_args(file, user_ptr,
> +							     array_buf,
> +							     array_size,
> +							     orig_cmd,
>  							     parg);

orig_cmd and pargs would fit on the same line if you want to.

Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>

>  			if (put_err)
>  				err = put_err;
> -		} else if (copy_to_user(user_ptr, mbuf, array_size)) {
> +		} else if (copy_to_user(user_ptr, array_buf, array_size)) {
>  			err = -EFAULT;
>  		}
>  		goto out_array_args;
> @@ -3381,6 +3377,7 @@ video_usercopy(struct file *file, unsigned int orig_cmd, unsigned long arg,
>  	if (video_put_user((void __user *)arg, parg, cmd, orig_cmd))
>  		err = -EFAULT;
>  out:
> +	kvfree(array_buf);
>  	kvfree(mbuf);
>  	return err;
>  }