Re: [PATCH] hfsplus: Supports freeing newly created tree head

[Viacheslav Dubeyko]

On Fri, 2026-04-17 at 14:58 +0800, Edward Adam Davis wrote:
> hfs_bnode_put() does not support deallocating a newly created btree
> head node; therefore, regardless of whether hfsplus_bnode_find() succeeds
> or fails, it cannot effectively reclaim the memory allocated for a newly
> created head node.
> 
> When finding a head node, if the node is a newly created one, we can use
> hfs_bnode_free() to reclaim its memory.
> 
> [1]
> BUG: memory leak
> unreferenced object 0xffff88811cabc840 (size 96):
>   backtrace (crc 3e2dadb7):
>     __hfs_bnode_create+0x59/0x310 fs/hfsplus/bnode.c:469
>     hfsplus_bnode_find+0x13e/0x580 fs/hfsplus/bnode.c:547
>     hfsplus_btree_open+0x2fa/0x6d0 fs/hfsplus/btree.c:382
>     hfsplus_fill_super+0x272/0x880 fs/hfsplus/super.c:548

I need slightly more detailed and clear explanation how the issue has been
happened and why we need to fix it in a such way. Currently, I don't have the
complete picture how this happened. I am sure that you have the complete
picture. :) Could you please share what you have in your mind? :) Don't hide the
wisdom. ;)

Thanks,
Slava.

> 
> Fixes: 8ad2c6a36ac4 ("hfsplus: validate b-tree node 0 bitmap at mount time")
> Reported-by: syzbot+98547b0428b6a6a3467c@xxxxxxxxxxxxxxxxxxxxxxxxx
> Closes: https://syzkaller.appspot.com/bug?extid=98547b0428b6a6a3467c
> Tested-by: syzbot+98547b0428b6a6a3467c@xxxxxxxxxxxxxxxxxxxxxxxxx
> Signed-off-by: Edward Adam Davis <eadavis@xxxxxx>
> ---
>  fs/hfsplus/bnode.c | 16 ++++++++++++----
>  1 file changed, 12 insertions(+), 4 deletions(-)
> 
> diff --git a/fs/hfsplus/bnode.c b/fs/hfsplus/bnode.c
> index f8b5a8ae58ff..65902104882a 100644
> --- a/fs/hfsplus/bnode.c
> +++ b/fs/hfsplus/bnode.c
> @@ -598,14 +598,18 @@ struct hfs_bnode *hfs_bnode_find(struct hfs_btree *tree, u32 num)
>  		if (key_size >= entry_size || key_size & 1)
>  			goto node_error;
>  	}
> -	clear_bit(HFS_BNODE_NEW, &node->flags);
> -	wake_up(&node->lock_wq);
> +	if (num != HFSPLUS_TREE_HEAD) {
> +		clear_bit(HFS_BNODE_NEW, &node->flags);
> +		wake_up(&node->lock_wq);
> +	}
>  	return node;
>  
>  node_error:
>  	set_bit(HFS_BNODE_ERROR, &node->flags);
> -	clear_bit(HFS_BNODE_NEW, &node->flags);
> -	wake_up(&node->lock_wq);
> +	if (num != HFSPLUS_TREE_HEAD) {
> +		clear_bit(HFS_BNODE_NEW, &node->flags);
> +		wake_up(&node->lock_wq);
> +	}
>  	hfs_bnode_put(node);
>  	return ERR_PTR(-EIO);
>  }
> @@ -694,6 +698,10 @@ void hfs_bnode_put(struct hfs_bnode *node)
>  			hfs_bnode_free(node);
>  			return;
>  		}
> +		if (test_bit(HFS_BNODE_NEW, &node->flags)) {
> +			hfs_bnode_unhash(node);
> +			hfs_bnode_free(node);
> +		}
>  		spin_unlock(&tree->hash_lock);
>  	}
>  }