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From:   Kuniyuki Iwashima <kuniyu@amazon.com>
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Subject: Re: [PATCH bpf-next 1/2] bpf, net: Support SO_REUSEPORT sockets with bpf_sk_assign
Date:   Thu, 25 May 2023 19:49:31 -0700
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From: Kuniyuki Iwashima <kuniyu@amazon.com>
Date: Thu, 25 May 2023 18:43:17 -0700
> From: Martin KaFai Lau <martin.lau@linux.dev>
> Date: Thu, 25 May 2023 16:42:46 -0700
> > On 5/25/23 1:19 AM, Lorenz Bauer wrote:
> > > diff --git a/include/net/inet6_hashtables.h b/include/net/inet6_hashtables.h
> > > index 56f1286583d3..3ba4dc2703da 100644
> > > --- a/include/net/inet6_hashtables.h
> > > +++ b/include/net/inet6_hashtables.h
> > > @@ -48,6 +48,13 @@ struct sock *__inet6_lookup_established(struct net *net,
> > >   					const u16 hnum, const int dif,
> > >   					const int sdif);
> > >   
> > > +struct sock *inet6_lookup_reuseport(struct net *net, struct sock *sk,
> > > +				    struct sk_buff *skb, int doff,
> > > +				    const struct in6_addr *saddr,
> > > +				    __be16 sport,
> > > +				    const struct in6_addr *daddr,
> > > +				    unsigned short hnum);
> > > +
> > >   struct sock *inet6_lookup_listener(struct net *net,
> > >   				   struct inet_hashinfo *hashinfo,
> > >   				   struct sk_buff *skb, int doff,
> > > @@ -85,14 +92,33 @@ static inline struct sock *__inet6_lookup_skb(struct inet_hashinfo *hashinfo,
> > >   					      int iif, int sdif,
> > >   					      bool *refcounted)
> > >   {
> > > -	struct sock *sk = skb_steal_sock(skb, refcounted);
> > > -
> > > +	bool prefetched;
> > > +	struct sock *sk = skb_steal_sock(skb, refcounted, &prefetched);
> > > +	struct net *net = dev_net(skb_dst(skb)->dev);
> > > +	const struct ipv6hdr *ip6h = ipv6_hdr(skb);
> > > +
> > > +	if (prefetched) {
> > > +		struct sock *reuse_sk = inet6_lookup_reuseport(net, sk, skb, doff,
> > 
> > If sk is TCP_ESTABLISHED, I suspect sk->sk_reuseport is 1 (from sk_clone)?
> 
> Exactly, it will cause null-ptr-deref in reuseport_select_sock().

Sorry, this doesn't occur.  reuseport_select_sock() has null check.


> We may want to use rcu_access_pointer(sk->sk_reuseport_cb) in
> each lookup_reuseport() instead of adding sk_state check ?

And if someone has a weird program that creates multiple listeners and
disable SO_REUSEPORT for a listener that hits first in lhash2, checking
sk_reuseport_cb might not work ?  I hope no one does such though, checking
sk_reuseport and sk_state could be better.

> 
> 
> > 
> > If it is, it should still work other than an extra inet6_ehashfn. Does it worth 
> > an extra sk->sk_state check or it is overkill?
> > 
> > 
> > > +							       &ip6h->saddr, sport,
> > > +							       &ip6h->daddr, ntohs(dport));