Re: [Linux-kernel-mentees] [PATCH] hfs, hfsplus: Fix NULL pointer dereference in hfs_find_init()

[Greg Kroah-Hartman]

On Wed, Aug 12, 2020 at 02:55:56AM -0400, Peilin Ye wrote:
> Prevent hfs_find_init() from dereferencing `tree` as NULL.
> 
> Reported-and-tested-by: syzbot+7ca256d0da4af073b2e2@xxxxxxxxxxxxxxxxxxxxxxxxx
> Signed-off-by: Peilin Ye <yepeilin.cs@xxxxxxxxx>
> ---
>  fs/hfs/bfind.c     | 3 +++
>  fs/hfsplus/bfind.c | 3 +++
>  2 files changed, 6 insertions(+)
> 
> diff --git a/fs/hfs/bfind.c b/fs/hfs/bfind.c
> index 4af318fbda77..880b7ea2c0fc 100644
> --- a/fs/hfs/bfind.c
> +++ b/fs/hfs/bfind.c
> @@ -16,6 +16,9 @@ int hfs_find_init(struct hfs_btree *tree, struct hfs_find_data *fd)
>  {
>  	void *ptr;
>  
> +	if (!tree)
> +		return -EINVAL;
> +
>  	fd->tree = tree;
>  	fd->bnode = NULL;
>  	ptr = kmalloc(tree->max_key_len * 2 + 4, GFP_KERNEL);
> diff --git a/fs/hfsplus/bfind.c b/fs/hfsplus/bfind.c
> index ca2ba8c9f82e..85bef3e44d7a 100644
> --- a/fs/hfsplus/bfind.c
> +++ b/fs/hfsplus/bfind.c
> @@ -16,6 +16,9 @@ int hfs_find_init(struct hfs_btree *tree, struct hfs_find_data *fd)
>  {
>  	void *ptr;
>  
> +	if (!tree)
> +		return -EINVAL;
> +

How can tree ever be NULL in these calls?  Shouldn't that be fixed as
the root problem here?

thanks,

greg k-h