[PATCH 5.15 211/691] nilfs2: determine empty node blocks as corrupted

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5.15-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Ryusuke Konishi <konishi.ryusuke@xxxxxxxxx>

[ Upstream commit 111b812d3662f3a1b831d19208f83aa711583fe6 ]

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@xxxxxxxxx
Fixes: 17c76b0104e4 ("nilfs2: B-tree based block mapping")
Signed-off-by: Ryusuke Konishi <konishi.ryusuke@xxxxxxxxx>
Cc: Lizhi Xu <lizhi.xu@xxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 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 fbb6ec56843f4..4de33c534e470 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







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