[PATCH 2/3] nilfs2: determine empty node blocks as corrupted

[Ryusuke Konishi]

Due to the nature of b-trees, nilfs2 itself and admin tools such as
mkfs.nilfs2 will never create an intermediate b-tree node block with 0
child nodes, nor will they delete (key, pointer)-entries that would
result in such a state.  However, it is possible that a b-tree node
block is corrupted on the backing device and is read with 0 child
nodes.

Because operation is not guaranteed if the number of child nodes is 0
for intermediate node blocks other than the root node, modify
nilfs_btree_node_broken(), which performs sanity checks when reading a
b-tree node block, so that such cases will be judged as metadata
corruption.

Signed-off-by: Ryusuke Konishi <konishi.ryusuke@xxxxxxxxx>
Fixes: 17c76b0104e4 ("nilfs2: B-tree based block mapping")
---
 fs/nilfs2/btree.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/nilfs2/btree.c b/fs/nilfs2/btree.c
index d390b8ba00d4..dedd3c480842 100644
--- a/fs/nilfs2/btree.c
+++ b/fs/nilfs2/btree.c
@@ -350,7 +350,7 @@ static int nilfs_btree_node_broken(const struct nilfs_btree_node *node,
 	if (unlikely(level < NILFS_BTREE_LEVEL_NODE_MIN ||
 		     level >= NILFS_BTREE_LEVEL_MAX ||
 		     (flags & NILFS_BTREE_NODE_ROOT) ||
-		     nchildren < 0 ||
+		     nchildren <= 0 ||
 		     nchildren > NILFS_BTREE_NODE_NCHILDREN_MAX(size))) {
 		nilfs_crit(inode->i_sb,
 			   "bad btree node (ino=%lu, blocknr=%llu): level = %d, flags = 0x%x, nchildren = %d",
-- 
2.43.0