Re: [PATCH v3 2/4] vfs,userns: Ensure real root is always capable towards inodes

[Serge Hallyn <serge.hallyn@ubuntu.com>]

Quoting Seth Forshee (seth.forshee@canonical.com):
> Currently root is restricted from performing some modifications
> to inodes whose owner is INVALID_UID or group is INVALID_GID
> because this id doesn't map into any user namespace. Add a
> special case to the relevant checks to make sure root is always
> capable of performing these operations.
> 
> Signed-off-by: Seth Forshee <seth.forshee@canonical.com>

(A case which was previously not possible.)

Acked-by: Serge E. Hallyn <serge.hallyn@ubuntu.com>

> ---
>  fs/inode.c          | 3 +++
>  kernel/capability.c | 6 +++++-
>  2 files changed, 8 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/inode.c b/fs/inode.c
> index 26753ba7b6d6..1029320ff029 100644
> --- a/fs/inode.c
> +++ b/fs/inode.c
> @@ -1840,6 +1840,9 @@ bool inode_owner_or_capable(const struct inode *inode)
>  {
>  	struct user_namespace *ns;
>  
> +	if (capable(CAP_SYS_ADMIN))
> +		return true;
> +
>  	if (uid_eq(current_fsuid(), inode->i_uid))
>  		return true;
>  
> diff --git a/kernel/capability.c b/kernel/capability.c
> index 989f5bfc57dc..a472eaa52b6a 100644
> --- a/kernel/capability.c
> +++ b/kernel/capability.c
> @@ -438,8 +438,12 @@ EXPORT_SYMBOL(capable);
>   */
>  bool capable_wrt_inode_uidgid(const struct inode *inode, int cap)
>  {
> -	struct user_namespace *ns = current_user_ns();
> +	struct user_namespace *ns;
>  
> +	if (capable(CAP_SYS_ADMIN))
> +		return true;
> +
> +	ns = current_user_ns();
>  	return ns_capable(ns, cap) && kuid_has_mapping(ns, inode->i_uid) &&
>  		kgid_has_mapping(ns, inode->i_gid);
>  }
> -- 
> 1.9.1
>