Re: [PATCH nf] nf_tables: nft_dynset: fix possible stateful expression memleak in error path

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

On Thu, Mar 12, 2026 at 12:02:37PM +0100, Florian Westphal wrote:
> Pablo Neira Ayuso <pablo@netfilter.org> wrote:
> > If cloning the second stateful expression in the element via GFP_ATOMIC
> > fails, then the first stateful expression remains in place without being
> > released.
> > 
> >    unreferenced object (percpu) 0x607b97e9cab8 (size 16):
> >      comm "softirq", pid 0, jiffies 4294931867
> >      hex dump (first 16 bytes on cpu 3):
> >        00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
> >      backtrace (crc 0):
> >        pcpu_alloc_noprof+0x453/0xd80
> >        nft_counter_clone+0x9c/0x190 [nf_tables]
> >        nft_expr_clone+0x8f/0x1b0 [nf_tables]
> >        nft_dynset_new+0x2cb/0x5f0 [nf_tables]
> >        nft_rhash_update+0x236/0x11c0 [nf_tables]
> >        nft_dynset_eval+0x11f/0x670 [nf_tables]
> >        nft_do_chain+0x253/0x1700 [nf_tables]
> >        nft_do_chain_ipv4+0x18d/0x270 [nf_tables]
> >        nf_hook_slow+0xaa/0x1e0
> >        ip_local_deliver+0x209/0x330
> > 
> > Pass NULL to nft_set_elem_expr_destroy() given stateful expressions do
> > not require context at this stage.
> 
> static void nft_connlimit_do_destroy(const struct nft_ctx *ctx,
>                                      struct nft_connlimit *priv)
> {
>         nf_ct_netns_put(ctx->net, ctx->family);
>         nf_conncount_cache_free(priv->list);
>         kfree(priv->list);
> }
> 
> I think minimal fake context could work though, the clone wasn't
> exposed to other cpus yet.
> 
> Other than this patch looks correct to me.

It is following this path:

static void nft_connlimit_destroy_clone(const struct nft_ctx *ctx,
                                        const struct nft_expr *expr)
{
        struct nft_connlimit *priv = nft_expr_priv(expr);
 
        nf_conncount_cache_free(priv->list);
        kfree(priv->list);
}

But I will post a v2 setting nft_ctx anyway.