btrfs: fix off-by-one when checking chunk map includes logical address

At btrfs_get_chunk_map() we get the extent map for the chunk that contains
the given logical address stored in the 'logical' argument. Then we do
sanity checks to verify the extent map contains the logical address. One
of these checks verifies if the extent map covers a range with an end
offset behind the target logical address - however this check has an
off-by-one error since it will consider an extent map whose start offset
plus its length matches the target logical address as inclusive, while
the fact is that the last byte it covers is behind the target logical
address (by 1).

So fix this condition by using '<=' rather than '<' when comparing the
extent map's "start + length" against the target logical address.

CC: stable@vger.kernel.org # 4.14+
Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

Author: fdmanana

fs/btrfs/volumes.c

@@ -3008,7 +3008,7 @@ struct extent_map *btrfs_get_chunk_map(struct btrfs_fs_info *fs_info,
 		return ERR_PTR(-EINVAL);
 	}
 
-	if (em->start > logical || em->start + em->len < logical) {
+	if (em->start > logical || em->start + em->len <= logical) {
 		btrfs_crit(fs_info,
 			   "found a bad mapping, wanted %llu-%llu, found %llu-%llu",
 			   logical, length, em->start, em->start + em->len);