Re: [PATCH] netfilter: mark racy access on ext->gen_id

Florian Westphal
2024-04-25T10:04:31Z

Eric Dumazet <edumazet@google.com> wrote:
> > There are a more uses ext->gen_id in the code, my understanding this
> > patch is just a stub.
>
> Anyway, ext->gen_id was already read and stored in @this_id
>
> I would probably avoid reading it a second time.

> diff --git a/net/netfilter/nf_conntrack_extend.c
> b/net/netfilter/nf_conntrack_extend.c
> index dd62cc12e7750734fec9be8a90fd0defcbc815e0..747797b20bc7417a2b7270d84f62d24991a4b982
> 100644
> --- a/net/netfilter/nf_conntrack_extend.c
> +++ b/net/netfilter/nf_conntrack_extend.c
> @@ -141,7 +141,7 @@ void *__nf_ct_ext_find(const struct nf_ct_ext *ext, u8 id)
> if (!__nf_ct_ext_exist(ext, id))
> return NULL;
>
> - if (this_id == 0 || ext->gen_id == gen_id)
> + if (this_id == 0 || this_id == gen_id)
> return (void *)ext + ext->offset[id];
>
> return NULL;
>

Right, that should work, unconfirmed entries are not exposed to other
cpus and confirmed entries get their id set to 0.