[PATCH v2] Btrfs: fix read_node_slot to return errors

[Liu Bo <bo.li.liu@oracle.com>]

We use read_node_slot() to read btree node and it has two cases,
a) slot is out of range, which means 'no such entry'
b) we fail to read the block, due to checksum fails or corrupted
   content or not with uptodate flag.
But we're returning NULL in both cases, this makes it return -ENOENT
in case a) and return -EIO in case b), and this fixes its callers
as well as btrfs_search_forward() 's caller to catch the new errors.

The problem is reported by Peter Becker, and I can manage to
hit the same BUG_ON by mounting my fuzz image.

Reported-by: Peter Becker <floyd.net@gmail.com>
Signed-off-by: Liu Bo <bo.li.liu@oracle.com>
---
v2: fix tree_move_down to check the correct extent buffer.

 fs/btrfs/ctree.c    | 69 +++++++++++++++++++++++++++++++++++++----------------
 fs/btrfs/tree-log.c |  4 ++++
 2 files changed, 52 insertions(+), 21 deletions(-)

diff --git a/fs/btrfs/ctree.c b/fs/btrfs/ctree.c
index a85cf7d..169deea 100644
--- a/fs/btrfs/ctree.c
+++ b/fs/btrfs/ctree.c
@@ -1858,7 +1858,6 @@ static void root_sub_used(struct btrfs_root *root, u32 size)
 
 /* given a node and slot number, this reads the blocks it points to.  The
  * extent buffer is returned with a reference taken (but unlocked).
- * NULL is returned on error.
  */
 static noinline struct extent_buffer *read_node_slot(struct btrfs_root *root,
 				   struct extent_buffer *parent, int slot)
@@ -1866,19 +1865,16 @@ static noinline struct extent_buffer *read_node_slot(struct btrfs_root *root,
 	int level = btrfs_header_level(parent);
 	struct extent_buffer *eb;
 
-	if (slot < 0)
-		return NULL;
-	if (slot >= btrfs_header_nritems(parent))
-		return NULL;
+	if (slot < 0 || slot >= btrfs_header_nritems(parent))
+		return ERR_PTR(-ENOENT);
 
 	BUG_ON(level == 0);
 
 	eb = read_tree_block(root, btrfs_node_blockptr(parent, slot),
 			     btrfs_node_ptr_generation(parent, slot));
-	if (IS_ERR(eb) || !extent_buffer_uptodate(eb)) {
-		if (!IS_ERR(eb))
-			free_extent_buffer(eb);
-		eb = NULL;
+	if (!IS_ERR(eb) && !extent_buffer_uptodate(eb)) {
+		free_extent_buffer(eb);
+		eb = ERR_PTR(-EIO);
 	}
 
 	return eb;
@@ -1931,8 +1927,8 @@ static noinline int balance_level(struct btrfs_trans_handle *trans,
 
 		/* promote the child to a root */
 		child = read_node_slot(root, mid, 0);
-		if (!child) {
-			ret = -EROFS;
+		if (IS_ERR(child)) {
+			ret = PTR_ERR(child);
 			btrfs_handle_fs_error(root->fs_info, ret, NULL);
 			goto enospc;
 		}
@@ -1970,6 +1966,9 @@ static noinline int balance_level(struct btrfs_trans_handle *trans,
 		return 0;
 
 	left = read_node_slot(root, parent, pslot - 1);
+	if (IS_ERR(left))
+		left = NULL;
+
 	if (left) {
 		btrfs_tree_lock(left);
 		btrfs_set_lock_blocking(left);
@@ -1980,7 +1979,11 @@ static noinline int balance_level(struct btrfs_trans_handle *trans,
 			goto enospc;
 		}
 	}
+
 	right = read_node_slot(root, parent, pslot + 1);
+	if (IS_ERR(right))
+		right = NULL;
+
 	if (right) {
 		btrfs_tree_lock(right);
 		btrfs_set_lock_blocking(right);
@@ -2135,6 +2138,8 @@ static noinline int push_nodes_for_insert(struct btrfs_trans_handle *trans,
 		return 1;
 
 	left = read_node_slot(root, parent, pslot - 1);
+	if (IS_ERR(left))
+		left = NULL;
 
 	/* first, try to make some room in the middle buffer */
 	if (left) {
@@ -2185,6 +2190,8 @@ static noinline int push_nodes_for_insert(struct btrfs_trans_handle *trans,
 		free_extent_buffer(left);
 	}
 	right = read_node_slot(root, parent, pslot + 1);
+	if (IS_ERR(right))
+		right = NULL;
 
 	/*
 	 * then try to empty the right most buffer into the middle
@@ -3773,7 +3780,11 @@ static int push_leaf_right(struct btrfs_trans_handle *trans, struct btrfs_root
 	btrfs_assert_tree_locked(path->nodes[1]);
 
 	right = read_node_slot(root, upper, slot + 1);
-	if (right == NULL)
+	/*
+	 * slot + 1 is not valid or we fail to read the right node,
+	 * no big deal, just return.
+	 */
+	if (IS_ERR(right))
 		return 1;
 
 	btrfs_tree_lock(right);
@@ -4003,7 +4014,11 @@ static int push_leaf_left(struct btrfs_trans_handle *trans, struct btrfs_root
 	btrfs_assert_tree_locked(path->nodes[1]);
 
 	left = read_node_slot(root, path->nodes[1], slot - 1);
-	if (left == NULL)
+	/*
+	 * slot - 1 is not valid or we fail to read the left node,
+	 * no big deal, just return.
+	 */
+	if (IS_ERR(left))
 		return 1;
 
 	btrfs_tree_lock(left);
@@ -5210,7 +5225,10 @@ find_next_key:
 		}
 		btrfs_set_path_blocking(path);
 		cur = read_node_slot(root, cur, slot);
-		BUG_ON(!cur); /* -ENOMEM */
+		if (IS_ERR(cur)) {
+			ret = PTR_ERR(cur);
+			goto out;
+		}
 
 		btrfs_tree_read_lock(cur);
 
@@ -5229,15 +5247,21 @@ out:
 	return ret;
 }
 
-static void tree_move_down(struct btrfs_root *root,
+static int tree_move_down(struct btrfs_root *root,
 			   struct btrfs_path *path,
 			   int *level, int root_level)
 {
+	struct extent_buffer *eb;
+
 	BUG_ON(*level == 0);
-	path->nodes[*level - 1] = read_node_slot(root, path->nodes[*level],
-					path->slots[*level]);
+	eb = read_node_slot(root, path->nodes[*level], path->slots[*level]);
+	if (IS_ERR(eb))
+		return PTR_ERR(eb);
+
+	path->nodes[*level - 1] = eb;
 	path->slots[*level - 1] = 0;
 	(*level)--;
+	return 0;
 }
 
 static int tree_move_next_or_upnext(struct btrfs_root *root,
@@ -5282,8 +5306,7 @@ static int tree_advance(struct btrfs_root *root,
 	if (*level == 0 || !allow_down) {
 		ret = tree_move_next_or_upnext(root, path, level, root_level);
 	} else {
-		tree_move_down(root, path, level, root_level);
-		ret = 0;
+		ret = tree_move_down(root, path, level, root_level);
 	}
 	if (ret >= 0) {
 		if (*level == 0)
@@ -5457,8 +5480,10 @@ int btrfs_compare_trees(struct btrfs_root *left_root,
 					left_root_level,
 					advance_left != ADVANCE_ONLY_NEXT,
 					&left_key);
-			if (ret < 0)
+			if (ret == -1)
 				left_end_reached = ADVANCE;
+			else if (ret < 0)
+				goto out;
 			advance_left = 0;
 		}
 		if (advance_right && !right_end_reached) {
@@ -5466,8 +5491,10 @@ int btrfs_compare_trees(struct btrfs_root *left_root,
 					right_root_level,
 					advance_right != ADVANCE_ONLY_NEXT,
 					&right_key);
-			if (ret < 0)
+			if (ret == -1)
 				right_end_reached = ADVANCE;
+			else if (ret < 0)
+				goto out;
 			advance_right = 0;
 		}
 
diff --git a/fs/btrfs/tree-log.c b/fs/btrfs/tree-log.c
index c05f69a..aa4475e 100644
--- a/fs/btrfs/tree-log.c
+++ b/fs/btrfs/tree-log.c
@@ -4703,6 +4703,10 @@ static int btrfs_log_inode(struct btrfs_trans_handle *trans,
 		ins_nr = 0;
 		ret = btrfs_search_forward(root, &min_key,
 					   path, trans->transid);
+		if (ret < 0) {
+			err = ret;
+			goto out_unlock;
+		}
 		if (ret != 0)
 			break;
 again:
-- 
2.5.5