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

[Florian Westphal <fw@strlen.de>]

Pablo Neira Ayuso <pablo@netfilter.org> wrote:
> 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);
> }

Oh, I see -- you are right, this follows the destroy_expr special case.

> But I will post a v2 setting nft_ctx anyway.

Thanks, I find it hard to assert correctness otherwise.