Re: [PATCH nft 3/3] netlink_linearize: skip set element expression in map statement key

[Phil Sutter <phil@nwl.cc>]

On Tue, Sep 26, 2023 at 05:25:00PM +0200, Pablo Neira Ayuso wrote:
> This fix is similar to 22d201010919 ("netlink_linearize: skip set element
> expression in set statement key") to fix map statement.
> 
> netlink_gen_map_stmt() relies on the map key, that is expressed as a set
> element. Use the set element key instead to skip the set element wrap,
> otherwise get_register() abort execution:
> 
>   nft: netlink_linearize.c:650: netlink_gen_expr: Assertion `dreg < ctx->reg_low' failed.
> 
> Reported-by: Luci Stanescu <luci@cnix.ro>
> Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

This patch adds map stmt printing and parsing support to JSON, but not a
word about that in the commit message. Did this slip in by accident
(e.g.  'git commit -a')? Anyway, I think it should go into a separate
patch.

[...]
> diff --git a/src/netlink_linearize.c b/src/netlink_linearize.c
> index 53a318aa2e62..99ed9f387a81 100644
> --- a/src/netlink_linearize.c
> +++ b/src/netlink_linearize.c
> @@ -1585,13 +1585,13 @@ static void netlink_gen_map_stmt(struct netlink_linearize_ctx *ctx,
>  	int num_stmts = 0;
>  	struct stmt *this;
>  
> -	sreg_key = get_register(ctx, stmt->map.key);
> -	netlink_gen_expr(ctx, stmt->map.key, sreg_key);
> +	sreg_key = get_register(ctx, stmt->set.key->key);
> +	netlink_gen_expr(ctx, stmt->set.key->key, sreg_key);
>  
>  	sreg_data = get_register(ctx, stmt->map.data);
>  	netlink_gen_expr(ctx, stmt->map.data, sreg_data);
>  
> -	release_register(ctx, stmt->map.key);
> +	release_register(ctx, stmt->set.key->key);
>  	release_register(ctx, stmt->map.data);
>  
>  	nle = alloc_nft_expr("dynset");

Any particular reason why this doesn't just use stmt->map.key->key? The
first two fields in structs set_stmt and map_stmt are identical, so the
above works "by accident".

Cheers, Phil