Re: [nf PATCH v3] netfilter: nfnetlink: Fix for interrupted hook dumps

[Phil Sutter <phil@nwl.cc>]

Hi Pablo,

On Mon, Sep 07, 2026 at 08:19:47PM +0200, Pablo Neira Ayuso wrote:
> On Fri, Sep 04, 2026 at 02:52:15PM +0200, Phil Sutter wrote:
> > @@ -338,27 +337,47 @@ nfnl_hook_entries_head(u8 pf, unsigned int hook, struct net *net, const char *de
> >  }
> >  
> >  static int nfnl_hook_dump_nat(struct sk_buff *nlskb,
> > -			      const struct nfnl_dump_hook_data *ctx,
> > -			      const struct nf_hook_ops *ops,
> > -			      int family, unsigned int seq)
> > +			      struct netlink_callback *cb,
> > +			      const struct nf_hook_ops *ops, int family)
> >  {
> >  	struct nf_nat_lookup_hook_priv *priv = ops->priv;
> > -	struct nf_hook_entries *e = rcu_dereference(priv->entries);
> > +	struct nfnl_dump_hook_data *ctx = cb->data;
> > +	struct net *net = sock_net(nlskb->sk);
> >  	struct nf_hook_ops **nat_ops;
> > -	int i, err;
> > +	unsigned int i = cb->args[1];
> > +	struct nf_hook_entries *e;
> > +	unsigned int base_seq;
> > +	int err = 0;
> >  
> > +	base_seq = smp_load_acquire(&net->nf.nat_hook_base_seq);
> 
> Maybe annnotate this base sequence in the .start via:
> 
> struct netlink_dump_control c = {
>         .start = ...;
> 
> We should probably start doing this in other nfnetlink subsystems too.
> 
> This will help catch an interference between two netlink recv() calls
> which results in calling netlink_dump() which calls this function.

I do not comprehend, sorry. The concurrent hook dumps have distinct cb
buffers and net->nf.{nat_,}hook_base_seq is shared but read-only. How
does the problematic interference happen?

Cheers, Phil