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_ioc_swapext(
	xfs_swapext_t	*sxp)
{
	xfs_inode_t     *ip, *tip;
	struct fd	f, tmp;
	int		error = 0;

	/* Pull information for the target fd */
	f = fdget((int)sxp->sx_fdtarget);
	if (!f.file) {
		error = XFS_ERROR(EINVAL);
		goto out;
	}

	if (!(f.file->f_mode & FMODE_WRITE) ||
	    !(f.file->f_mode & FMODE_READ) ||
	    (f.file->f_flags & O_APPEND)) {
		error = XFS_ERROR(EBADF);
		goto out_put_file;
	}

	tmp = fdget((int)sxp->sx_fdtmp);
	if (!tmp.file) {
		error = XFS_ERROR(EINVAL);
		goto out_put_file;
	}

	if (!(tmp.file->f_mode & FMODE_WRITE) ||
	    !(tmp.file->f_mode & FMODE_READ) ||
	    (tmp.file->f_flags & O_APPEND)) {
		error = XFS_ERROR(EBADF);
		goto out_put_tmp_file;
	}

	if (IS_SWAPFILE(file_inode(f.file)) ||
	    IS_SWAPFILE(file_inode(tmp.file))) {
		error = XFS_ERROR(EINVAL);
		goto out_put_tmp_file;
	}

	ip = XFS_I(file_inode(f.file));
	tip = XFS_I(file_inode(tmp.file));

	if (ip->i_mount != tip->i_mount) {
		error = XFS_ERROR(EINVAL);
		goto out_put_tmp_file;
	}

	if (ip->i_ino == tip->i_ino) {
		error = XFS_ERROR(EINVAL);
		goto out_put_tmp_file;
	}

	if (XFS_FORCED_SHUTDOWN(ip->i_mount)) {
		error = XFS_ERROR(EIO);
		goto out_put_tmp_file;
	}

	error = xfs_swap_extents(ip, tip, sxp);

 out_put_tmp_file:
	fdput(tmp);
 out_put_file:
	fdput(f);
 out:
	return error;
}

xfs_ioc_swapext(
	xfs_swapext_t	*sxp)
{
	xfs_inode_t     *ip, *tip;
	struct fd	f, tmp;
	int		error = 0;

	/* Pull information for the target fd */
	f = fdget((int)sxp->sx_fdtarget);
	if (!f.file) {
		error = XFS_ERROR(EINVAL);
		goto out;
	}

	if (!(f.file->f_mode & FMODE_WRITE) ||
	    !(f.file->f_mode & FMODE_READ) ||
	    (f.file->f_flags & O_APPEND)) {
		error = XFS_ERROR(EBADF);
		goto out_put_file;
	}

	tmp = fdget((int)sxp->sx_fdtmp);
	if (!tmp.file) {
		error = XFS_ERROR(EINVAL);
		goto out_put_file;
	}

	if (!(tmp.file->f_mode & FMODE_WRITE) ||
	    !(tmp.file->f_mode & FMODE_READ) ||
	    (tmp.file->f_flags & O_APPEND)) {
		error = XFS_ERROR(EBADF);
		goto out_put_tmp_file;
	}

	if (IS_SWAPFILE(file_inode(f.file)) ||
	    IS_SWAPFILE(file_inode(tmp.file))) {
		error = XFS_ERROR(EINVAL);
		goto out_put_tmp_file;
	}

	ip = XFS_I(file_inode(f.file));
	tip = XFS_I(file_inode(tmp.file));

	if (ip->i_mount != tip->i_mount) {
		error = XFS_ERROR(EINVAL);
		goto out_put_tmp_file;
	}

	if (ip->i_ino == tip->i_ino) {
		error = XFS_ERROR(EINVAL);
		goto out_put_tmp_file;
	}

	if (XFS_FORCED_SHUTDOWN(ip->i_mount)) {
		error = XFS_ERROR(EIO);
		goto out_put_tmp_file;
	}

	error = xfs_swap_extents(ip, tip, sxp);

 out_put_tmp_file:
	fdput(tmp);
 out_put_file:
	fdput(f);
 out:
	return error;
}
