[PATCH v3 2/7] userns: Simpilify MNT_NODEV handling.

[Andy Lutomirski]

On Wed, Sep 16, 2015 at 1:02 PM, Seth Forshee
<seth.forshee at canonical.com> wrote:
> From: "Eric W. Biederman" <ebiederm at xmission.com>
>
> - Consolidate the testing if a device node may be opened in a new
>   function may_open_dev.
>
> - Move the check for allowing access to device nodes on filesystems
>   not mounted in the initial user namespace from mount time to open
>   time and include it in may_open_dev.
>
> This set of changes removes the implicit adding of MNT_NODEV which
> simplifies the logic in fs/namespace.c and removes a potentially
> problematic user visible difference in how normal and unprivileged
> mount namespaces work.
>
> Signed-off-by: "Eric W. Biederman" <ebiederm at xmission.com>

> -               /* Only in special cases allow devices from mounts
> -                * created outside the initial user namespace.
> -                */
> -               if (!(type->fs_flags & FS_USERNS_DEV_MOUNT)) {
> -                       flags |= MS_NODEV;
> -                       mnt_flags |= MNT_NODEV | MNT_LOCK_NODEV;
> -               }

This is an ABI change.  It's probably okay, but I think the commit
message should make it clear what's happening.


--Andy