Re: [PATCH nft] src: netlink: fix crash when ops doesn't support udata

[Pablo Neira Ayuso <pablo@netfilter.org>]

On Thu, May 08, 2025 at 04:29:04PM +0200, Florian Westphal wrote:
> Whenever a new version adds udata support to an expression, then old
> versions of nft will crash when trying to list such a ruleset generated
> by a more recent version of nftables.
> 
> Fix this by falling back to 'type' format.

Fixes: 6e48df5329ea ('src: add "typeof" build/parse/print support')

> Signed-off-by: Florian Westphal <fw@strlen.de>

Reviewed-by: Pablo Neira Ayuso <pablo@netfilter.org>

Thanks.

> ---
>  src/netlink.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/src/netlink.c b/src/netlink.c
> index 25ee3419772b..5825a68d03bc 100644
> --- a/src/netlink.c
> +++ b/src/netlink.c
> @@ -913,7 +913,7 @@ static struct expr *set_make_key(const struct nftnl_udata *attr)
>  
>  	etype = nftnl_udata_get_u32(ud[NFTNL_UDATA_SET_TYPEOF_EXPR]);
>  	ops = expr_ops_by_type_u32(etype);
> -	if (!ops)
> +	if (!ops || !ops->parse_udata)
>  		return NULL;
>  
>  	expr = ops->parse_udata(ud[NFTNL_UDATA_SET_TYPEOF_DATA]);
> -- 
> 2.49.0
> 
>