[PATCH 1/5] fs: Verify access of user towards block device file when mounting

[Seth Forshee]

On Thu, Oct 01, 2015 at 10:40:08AM -0500, Eric W. Biederman wrote:
> Seth Forshee <seth.forshee at canonical.com> writes:
> 
> > When mounting a filesystem on a block device there is currently
> > no verification that the user has appropriate access to the
> > device file passed to mount. This has not been an issue so far
> > since the user in question has always been root, but this must
> > be changed before allowing unprivileged users to mount in user
> > namespaces.
> >
> > To fix this, add an argument to lookup_bdev() to specify the
> > required permissions. If the mask of permissions is zero, or
> > if the user has CAP_SYS_ADMIN, the permission check is skipped,
> > otherwise the lookup fails if the user does not have the
> > specified access rights for the inode at the supplied path.
> >
> > Callers associated with mounting are updated to pass permission
> > masks to lookup_bdev() so that these mounts will fail for an
> > unprivileged user who lacks permissions for the block device
> > inode. All other callers pass 0 to maintain their current
> > behaviors.
> >
> 
> Seth can you split this patch?
> 
> One patch to add an argument to lookup_bdev,
> and then for each kind of callsite a follow-on patch (if we are ready
> for that).
> 
> That will separate the logical changes and make things easier to track
> via bisect and more importantly easier to review things.

Sure, I'll do that.

Seth