[PATCH 2/2 v2] staging: android: ashmem: Fix mmap size validation

[Joel Fernandes]

On Tue, Jun 19, 2018 at 05:57:35PM -0700, Alistair Strachan wrote:
> The ashmem driver did not check that the size/offset of the vma passed
> to its .mmap() function was not larger than the ashmem object being
> mapped. This could cause mmap() to succeed, even though accessing parts
> of the mapping would later fail with a segmentation fault.
> 
> Ensure an error is returned by the ashmem_mmap() function if the vma
> size is larger than the ashmem object size. This enables safer handling
> of the problem in userspace.
> 
> Cc: Greg Kroah-Hartman <gregkh at linuxfoundation.org>
> Cc: Arve Hjønnevåg <arve at android.com>
> Cc: Todd Kjos <tkjos at android.com>
> Cc: Martijn Coenen <maco at android.com>
> Cc: devel at driverdev.osuosl.org
> Cc: linux-kernel at vger.kernel.org
> Cc: kernel-team at android.com
> Cc: Joel Fernandes <joel at joelfernandes.org>
> Signed-off-by: Alistair Strachan <astrachan at google.com>
> ---
> v2: Removed unnecessary use of unlikely() macro
> 
>  drivers/staging/android/ashmem.c | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/drivers/staging/android/ashmem.c b/drivers/staging/android/ashmem.c
> index c6386e4f5c9b..e392358ec244 100644
> --- a/drivers/staging/android/ashmem.c
> +++ b/drivers/staging/android/ashmem.c
> @@ -366,6 +366,12 @@ static int ashmem_mmap(struct file *file, struct vm_area_struct *vma)
>  		goto out;
>  	}
>  
> +	/* requested mapping size larger than object size */
> +	if (vma->vm_end - vma->vm_start > PAGE_ALIGN(asma->size)) {
> +		ret = -EINVAL;
> +		goto out;
> +	}
> +

Acked-by: Joel Fernandes (Google) <joel at joelfernandes.org>

thanks,

 - Joel