Re: [PATCH] hfs, hfsplus: remove WARN_ON when new bnode already hashed

[Viacheslav Dubeyko]

On Mon, 2026-06-22 at 17:17 +0000, Aditya Srivastava wrote:
> From: Aditya Prakash Srivastava <aditya.ansh182@xxxxxxxxx>
> 
> Syzbot reported a warning in hfsplus_bnode_create() when mounting and
> traversing a fuzzed/corrupted disk image.
> 
> The warning is triggered because the node index is found to be
> already
> active and hashed in the btree hash table, which indicates on-disk
> metadata corruption.
> 
> Filesystem corruption should be handled gracefully by returning an
> error
> and logging a message, rather than triggering kernel-level warnings
> (which can panic the system under panic_on_warn=1 configurations).
> The code already prints a critical message and returns -EEXIST (or
> the
> node in hfs), so the WARN_ON() is completely redundant and dangerous.
> 
> Remove the WARN_ON(1) from both hfs_bnode_create() and
> hfsplus_bnode_create().
> 
> Reported-by: syzbot+2bf21610eea63cb2ce93@xxxxxxxxxxxxxxxxxxxxxxxxx
> Closes: https://syzkaller.appspot.com/bug?extid=2bf21610eea63cb2ce93
> Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
> Signed-off-by: Aditya Prakash Srivastava <aditya.ansh182@xxxxxxxxx>
> ---
>  fs/hfs/bnode.c     | 1 -
>  fs/hfsplus/bnode.c | 1 -
>  2 files changed, 2 deletions(-)
> 
> diff --git a/fs/hfs/bnode.c b/fs/hfs/bnode.c
> index 13d58c51fc46..335834961741 100644
> --- a/fs/hfs/bnode.c
> +++ b/fs/hfs/bnode.c
> @@ -517,7 +517,6 @@ struct hfs_bnode *hfs_bnode_create(struct
> hfs_btree *tree, u32 num)
>  	spin_unlock(&tree->hash_lock);
>  	if (node) {
>  		pr_crit("new node %u already hashed?\n", num);
> -		WARN_ON(1);
>  		return node;
>  	}
>  	node = __hfs_bnode_create(tree, num);
> diff --git a/fs/hfsplus/bnode.c b/fs/hfsplus/bnode.c
> index f8b5a8ae58ff..bfc2a7f53edd 100644
> --- a/fs/hfsplus/bnode.c
> +++ b/fs/hfsplus/bnode.c
> @@ -631,7 +631,6 @@ struct hfs_bnode *hfs_bnode_create(struct
> hfs_btree *tree, u32 num)
>  	spin_unlock(&tree->hash_lock);
>  	if (node) {
>  		pr_crit("new node %u already hashed?\n", num);
> -		WARN_ON(1);
>  		return ERR_PTR(-EEXIST);
>  	}
>  	node = __hfs_bnode_create(tree, num);

If we have corrupted HFS/HFS+ volume and we can detect it during the
mount operation, then we should not mount the corrupted volume or mount
in READ-ONLY mode. As I remember, we already have HFS+ logic that
detects b-tree's map corruption for the case of node 0. We haven't this
logic for HFS file system logic yet, if I remember correctly. So, you
are welcomed to port this logic for HFS case. Removing WARN_ON() simply
hides the potential issues. So, I don't think that we need to remove
it.

Thanks,
Slava.