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_merge_ioc_xflags(
	unsigned int	flags,
	unsigned int	start)
{
	unsigned int	xflags = start;

	if (flags & FS_IMMUTABLE_FL)
		xflags |= XFS_XFLAG_IMMUTABLE;
	else
		xflags &= ~XFS_XFLAG_IMMUTABLE;
	if (flags & FS_APPEND_FL)
		xflags |= XFS_XFLAG_APPEND;
	else
		xflags &= ~XFS_XFLAG_APPEND;
	if (flags & FS_SYNC_FL)
		xflags |= XFS_XFLAG_SYNC;
	else
		xflags &= ~XFS_XFLAG_SYNC;
	if (flags & FS_NOATIME_FL)
		xflags |= XFS_XFLAG_NOATIME;
	else
		xflags &= ~XFS_XFLAG_NOATIME;
	if (flags & FS_NODUMP_FL)
		xflags |= XFS_XFLAG_NODUMP;
	else
		xflags &= ~XFS_XFLAG_NODUMP;

	return xflags;
}

xfs_merge_ioc_xflags(
	unsigned int	flags,
	unsigned int	start)
{
	unsigned int	xflags = start;

	if (flags & FS_IMMUTABLE_FL)
		xflags |= XFS_XFLAG_IMMUTABLE;
	else
		xflags &= ~XFS_XFLAG_IMMUTABLE;
	if (flags & FS_APPEND_FL)
		xflags |= XFS_XFLAG_APPEND;
	else
		xflags &= ~XFS_XFLAG_APPEND;
	if (flags & FS_SYNC_FL)
		xflags |= XFS_XFLAG_SYNC;
	else
		xflags &= ~XFS_XFLAG_SYNC;
	if (flags & FS_NOATIME_FL)
		xflags |= XFS_XFLAG_NOATIME;
	else
		xflags &= ~XFS_XFLAG_NOATIME;
	if (flags & FS_NODUMP_FL)
		xflags |= XFS_XFLAG_NODUMP;
	else
		xflags &= ~XFS_XFLAG_NODUMP;

	return xflags;
}
