nilfs2: determine empty node blocks as corrupted

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.

Link: https://lkml.kernel.org/r/20240904081401.16682-3-konishi.ryusuke@gmail.com
Fixes: 17c76b0104e4 ("nilfs2: B-tree based block mapping")
Signed-off-by: Ryusuke Konishi <konishi.ryusuke@gmail.com>
Cc: Lizhi Xu <lizhi.xu@windriver.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/fs/nilfs2/btree.c b/fs/nilfs2/btree.c
index d390b8ba00d45d4c5f589276f7d9e622bc91e9d1..dedd3c48084230b51697e1542fbc0362166871dd 100644 (file)
--- 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",