fs,userns: Change inode_capable to capable_wrt_inode_uidgid

The kernel has no concept of capabilities with respect to inodes; inodes
exist independently of namespaces.  For example, inode_capable(inode,
CAP_LINUX_IMMUTABLE) would be nonsense.

This patch changes inode_capable to check for uid and gid mappings and
renames it to capable_wrt_inode_uidgid, which should make it more
obvious what it does.

Fixes CVE-2014-4014.

Cc: Theodore Ts'o <tytso@mit.edu>
Cc: Serge Hallyn <serge.hallyn@ubuntu.com>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Dave Chinner <david@fromorbit.com>
Cc: stable@vger.kernel.org
Signed-off-by: Andy Lutomirski <luto@amacapital.net>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
xfs_getbmap_format(void **ap, struct getbmapx *bmv, int *full)
{
	struct getbmap __user	*base = *ap;

	/* copy only getbmap portion (not getbmapx) */
	if (copy_to_user(base, bmv, sizeof(struct getbmap)))
		return XFS_ERROR(EFAULT);

	*ap += sizeof(struct getbmap);
	return 0;
}

xfs_getbmap_format(void **ap, struct getbmapx *bmv, int *full)
{
	struct getbmap __user	*base = *ap;

	/* copy only getbmap portion (not getbmapx) */
	if (copy_to_user(base, bmv, sizeof(struct getbmap)))
		return XFS_ERROR(EFAULT);

	*ap += sizeof(struct getbmap);
	return 0;
}
