[PATCH 31/43] userns: Teach inode_capable to understand inodes whose uids map to other namespaces.

[Serge E. Hallyn]

Quoting Eric W. Beiderman (ebiederm at xmission.com):
> From: Eric W. Biederman <ebiederm at xmission.com>
> 
> Signed-off-by: Eric W. Biederman <ebiederm at xmission.com>

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

> ---
>  kernel/capability.c |    6 ++++--
>  1 files changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/kernel/capability.c b/kernel/capability.c
> index cc5f071..493d972 100644
> --- a/kernel/capability.c
> +++ b/kernel/capability.c
> @@ -429,12 +429,14 @@ bool nsown_capable(int cap)
>   * targeted at it's own user namespace and that the given inode is owned
>   * by the current user namespace or a child namespace.
>   *
> - * Currently inodes can only be owned by the initial user namespace.
> + * Currently we check to see if an inode is owned by the current
> + * user namespace by seeing if the inode's owner maps into the
> + * current user namespace.
>   *
>   */
>  bool inode_capable(const struct inode *inode, int cap)
>  {
>  	struct user_namespace *ns = current_user_ns();
>  
> -	return ns_capable(ns, cap) && (ns == &init_user_ns);
> +	return ns_capable(ns, cap) && kuid_has_mapping(ns, inode->i_uid);
>  }
> -- 
> 1.7.2.5
> 
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