squashfs: fix length field overlap check in metadata reading

This is a regression introduced by the "migrate from ll_rw_block usage
to BIO" patch.

Squashfs packs structures on byte boundaries, and due to that the length
field (of the metadata block) may not be fully in the current block.
The new code rewrote and introduced a faulty check for that edge case.

Fixes: 93e72b3 ("squashfs: migrate from ll_rw_block usage to BIO")
Reported-by: Bernd Amend <[email protected]>
Signed-off-by: Phillip Lougher <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Cc: Christoph Hellwig <[email protected]>
Cc: Adrien Schildknecht <[email protected]>
Cc: Guenter Roeck <[email protected]>
Cc: Daniel Rosenberg <[email protected]>
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Linus Torvalds <[email protected]>

Author: plougher

fs/squashfs/block.c

@@ -175,7 +175,7 @@ int squashfs_read_data(struct super_block *sb, u64 index, int length,
 		/* Extract the length of the metadata block */
 		data = page_address(bvec->bv_page) + bvec->bv_offset;
 		length = data[offset];
-		if (offset <= bvec->bv_len - 1) {
+		if (offset < bvec->bv_len - 1) {
 			length |= data[offset + 1] << 8;
 		} else {
 			if (WARN_ON_ONCE(!bio_next_segment(bio, &iter_all))) {