Btrfs: improve check_node to avoid reading corrupted nodes

BugLink: https://bugs.launchpad.net/bugs/1818237

commit 6b722c17 upstream.

We need to check items in a node to make sure that we're reading
a valid one, otherwise we could get various crashes while processing
delayed_refs.
Signed-off-by: Liu Bo <bo.li.liu@oracle.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
Signed-off-by: Ben Hutchings <ben.hutchings@codethink.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Juerg Haefliger <juergh@canonical.com>
Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>

fs/btrfs/disk-io.c

@@ -523,9 +523,10 @@ static int check_tree_block_fsid(struct btrfs_fs_info *fs_info,
 }
 
 #define CORRUPT(reason, eb, root, slot)				\
-	btrfs_crit(root->fs_info, "corrupt leaf, %s: block=%llu,"	\
-		   "root=%llu, slot=%d", reason,			\
-	       btrfs_header_bytenr(eb),	root->objectid, slot)
+	btrfs_crit(root->fs_info, "corrupt %s, %s: block=%llu,"	\
+		   " root=%llu, slot=%d",			\
+		   btrfs_header_level(eb) == 0 ? "leaf" : "node",\
+		   reason, btrfs_header_bytenr(eb), root->objectid, slot)
 
 static noinline int check_leaf(struct btrfs_root *root,
 			       struct extent_buffer *leaf)
@@ -616,6 +617,10 @@ static noinline int check_leaf(struct btrfs_root *root,
 static int check_node(struct btrfs_root *root, struct extent_buffer *node)
 {
 	unsigned long nr = btrfs_header_nritems(node);
+	struct btrfs_key key, next_key;
+	int slot;
+	u64 bytenr;
+	int ret = 0;
 
 	if (nr == 0 || nr > BTRFS_NODEPTRS_PER_BLOCK(root)) {
 		btrfs_crit(root->fs_info,
@@ -623,7 +628,26 @@ static int check_node(struct btrfs_root *root, struct extent_buffer *node)
 			   node->start, root->objectid, nr);
 		return -EIO;
 	}
-	return 0;
+
+	for (slot = 0; slot < nr - 1; slot++) {
+		bytenr = btrfs_node_blockptr(node, slot);
+		btrfs_node_key_to_cpu(node, &key, slot);
+		btrfs_node_key_to_cpu(node, &next_key, slot + 1);
+
+		if (!bytenr) {
+			CORRUPT("invalid item slot", node, root, slot);
+			ret = -EIO;
+			goto out;
+		}
+
+		if (btrfs_comp_cpu_keys(&key, &next_key) >= 0) {
+			CORRUPT("bad key order", node, root, slot);
+			ret = -EIO;
+			goto out;
+		}
+	}
+out:
+	return ret;
 }
 
 static int btree_readpage_end_io_hook(struct btrfs_io_bio *io_bio,