linux-kernel - [PATCH] bfs: reject inodes with zero link count in bfs

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Message-Id: <20260208185122.1115949-1-n7l8m4@u.northwestern.edu>
Date: Sun,  8 Feb 2026 18:51:22 +0000
From: Ziyi Guo <n7l8m4@...orthwestern.edu>
To: "Tigran A . Aivazian" <aivazian.tigran@...il.com>
Cc: linux-kernel@...r.kernel.org,
	Ziyi Guo <n7l8m4@...orthwestern.edu>
Subject: [PATCH] bfs: reject inodes with zero link count in bfs_iget()

bfs_iget() reads i_nlink directly from disk without validating that
it is non-zero. A corrupted BFS image with an inode that has
i_nlink == 0 but is still referenced by a directory entry allows that
inode to be loaded. While bfs_unlink() has a recovery guard for this
case, other functions like bfs_rename() calls inode_dec_link_count()
without checking, triggering WARN_ON(inode->i_nlink == 0) in drop_nlink().

Reject inodes with zero link count at load time, consistent with
the approach used by ext4, minix, nilfs2, and other filesystems.

Signed-off-by: Ziyi Guo <n7l8m4@...orthwestern.edu>
---
 fs/bfs/inode.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/fs/bfs/inode.c b/fs/bfs/inode.c
index ce6f83234b67..85d664e169f0 100644
--- a/fs/bfs/inode.c
+++ b/fs/bfs/inode.c
@@ -96,6 +96,10 @@ struct inode *bfs_iget(struct super_block *sb, unsigned long ino)
 	i_uid_write(inode, le32_to_cpu(di->i_uid));
 	i_gid_write(inode,  le32_to_cpu(di->i_gid));
 	set_nlink(inode, le32_to_cpu(di->i_nlink));
+	if (!inode->i_nlink) {
+		brelse(bh);
+		goto error;
+	}
 	inode->i_size = BFS_FILESIZE(di);
 	inode->i_blocks = BFS_FILEBLOCKS(di);
 	inode_set_atime(inode, le32_to_cpu(di->i_atime), 0);
-- 
2.34.1