isofs: Fix unbounded recursion when processing relocated directories

We did not check relocated directory in any way when processing Rock
Ridge 'CL' tag. Thus a corrupted isofs image can possibly have a CL
entry pointing to another CL entry leading to possibly unbounded
recursion in kernel code and thus stack overflow or deadlocks (if there
is a loop created from CL entries).

Fix the problem by not allowing CL entry to point to a directory entry
with CL entry (such use makes no good sense anyway) and by checking
whether CL entry doesn't point to itself.

CC: stable@vger.kernel.org
Reported-by: Chris Evans <cevans@google.com>
Signed-off-by: Jan Kara <jack@suse.cz>
static int isofs_statfs (struct dentry *dentry, struct kstatfs *buf)
{
	struct super_block *sb = dentry->d_sb;
	u64 id = huge_encode_dev(sb->s_bdev->bd_dev);

	buf->f_type = ISOFS_SUPER_MAGIC;
	buf->f_bsize = sb->s_blocksize;
	buf->f_blocks = (ISOFS_SB(sb)->s_nzones
		<< (ISOFS_SB(sb)->s_log_zone_size - sb->s_blocksize_bits));
	buf->f_bfree = 0;
	buf->f_bavail = 0;
	buf->f_files = ISOFS_SB(sb)->s_ninodes;
	buf->f_ffree = 0;
	buf->f_fsid.val[0] = (u32)id;
	buf->f_fsid.val[1] = (u32)(id >> 32);
	buf->f_namelen = NAME_MAX;
	return 0;
}

static int isofs_statfs (struct dentry *dentry, struct kstatfs *buf)
{
	struct super_block *sb = dentry->d_sb;
	u64 id = huge_encode_dev(sb->s_bdev->bd_dev);

	buf->f_type = ISOFS_SUPER_MAGIC;
	buf->f_bsize = sb->s_blocksize;
	buf->f_blocks = (ISOFS_SB(sb)->s_nzones
		<< (ISOFS_SB(sb)->s_log_zone_size - sb->s_blocksize_bits));
	buf->f_bfree = 0;
	buf->f_bavail = 0;
	buf->f_files = ISOFS_SB(sb)->s_ninodes;
	buf->f_ffree = 0;
	buf->f_fsid.val[0] = (u32)id;
	buf->f_fsid.val[1] = (u32)(id >> 32);
	buf->f_namelen = NAME_MAX;
	return 0;
}
