[PATCH 02/19] block_dev: Check permissions towards block device inode when mounting

[Serge E. Hallyn]

On Wed, Dec 02, 2015 at 09:40:02AM -0600, Seth Forshee wrote:
> Unprivileged users should not be able to mount block devices when
> they lack sufficient privileges towards the block device inode.
> Update blkdev_get_by_path() to validate that the user has the
> required access to the inode at the specified path. The check
> will be skipped for CAP_SYS_ADMIN, so privileged mounts will
> continue working as before.
> 
> Signed-off-by: Seth Forshee <seth.forshee at canonical.com>

Acked-by: Serge Hallyn <serge.hallyn at canonical.com>

> ---
>  fs/block_dev.c | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/block_dev.c b/fs/block_dev.c
> index 3ebbde85d898..4fdb6ab59816 100644
> --- a/fs/block_dev.c
> +++ b/fs/block_dev.c
> @@ -1424,9 +1424,14 @@ struct block_device *blkdev_get_by_path(const char *path, fmode_t mode,
>  					void *holder)
>  {
>  	struct block_device *bdev;
> +	int perm = 0;
>  	int err;
>  
> -	bdev = lookup_bdev(path, 0);
> +	if (mode & FMODE_READ)
> +		perm |= MAY_READ;
> +	if (mode & FMODE_WRITE)
> +		perm |= MAY_WRITE;
> +	bdev = lookup_bdev(path, perm);
>  	if (IS_ERR(bdev))
>  		return bdev;
>  
> -- 
> 1.9.1
> 
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