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Miller" , David Ahern , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Willem de Bruijn , Alexei Starovoitov , Daniel Borkmann , Andrii Nakryiko , Eduard Zingerman , Song Liu , Yonghong Song , John Fastabend , KP Singh , Stanislav Fomichev , Hao Luo , Jiri Olsa , Mykola Lysenko , Shuah Khan , netdev@vger.kernel.org, linux-kernel@vger.kernel.org, bpf@vger.kernel.org, linux-kselftest@vger.kernel.org, Jakub Sitnicki , kernel-team@cloudflare.com Subject: Re: [RFC PATCH 2/3] ipv6: Run a reverse sk_lookup on sendmsg. Message-ID: References: <20240913-reverse-sk-lookup-v1-0-e721ea003d4c@cloudflare.com> <20240913-reverse-sk-lookup-v1-2-e721ea003d4c@cloudflare.com> Precedence: bulk X-Mailing-List: linux-kselftest@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: On Fri, Sep 13, 2024 at 11:24:09AM -0700, Martin KaFai Lau wrote: > On 9/13/24 2:39 AM, Tiago Lam wrote: > > This follows the same rationale provided for the ipv4 counterpart, where > > it now runs a reverse socket lookup when source addresses and/or ports > > are changed, on sendmsg, to check whether egress traffic should be > > allowed to go through or not. > > > > As with ipv4, the ipv6 sendmsg path is also extended here to support the > > IPV6_ORIGDSTADDR ancilliary message to be able to specify a source > > address/port. > > > > Suggested-by: Jakub Sitnicki > > Signed-off-by: Tiago Lam > > --- > > net/ipv6/datagram.c | 76 +++++++++++++++++++++++++++++++++++++++++++++++++++++ > > net/ipv6/udp.c | 8 ++++-- > > 2 files changed, 82 insertions(+), 2 deletions(-) > > > > diff --git a/net/ipv6/datagram.c b/net/ipv6/datagram.c > > index fff78496803d..4214dda1c320 100644 > > --- a/net/ipv6/datagram.c > > +++ b/net/ipv6/datagram.c > > @@ -756,6 +756,27 @@ void ip6_datagram_recv_ctl(struct sock *sk, struct msghdr *msg, > > } > > EXPORT_SYMBOL_GPL(ip6_datagram_recv_ctl); > > +static inline bool reverse_sk_lookup(struct flowi6 *fl6, struct sock *sk, > > + struct in6_addr *saddr, __be16 sport) > > +{ > > + if (static_branch_unlikely(&bpf_sk_lookup_enabled) && > > + (saddr && sport) && > > + (ipv6_addr_cmp(&sk->sk_v6_rcv_saddr, saddr) || inet_sk(sk)->inet_sport != sport)) { > > + struct sock *sk_egress; > > + > > + bpf_sk_lookup_run_v6(sock_net(sk), IPPROTO_UDP, &fl6->daddr, fl6->fl6_dport, > > + saddr, ntohs(sport), 0, &sk_egress); > > iirc, in the ingress path, the sk could also be selected by a tc bpf prog > doing bpf_sk_assign. Then this re-run on sk_lookup may give an incorrect > result? > If it does give the incorrect result, we still fallback to the normal egress path. > In general, is it necessary to rerun any bpf prog if the user space has > specified the IP[v6]_ORIGDSTADDR. > More generally, wouldn't that also be the case if someone calls bpf_sk_assign() in both TC and sk_lookup on ingress? It can lead to some interference between the two. It seems like the interesting cases are: 1. Calling bpf_sk_assign() on both TC and sk_lookup ingress: if this happens sk_lookup on egress should match the correct socket when doing the reverse lookup; 2. Calling bpf_sk_assign() only on ingress TC: in this case it will depend if an sk_lookup program is attached or not: a. If not, there's no reverse lookup on egress either; b. But if yes, although the reverse sk_lookup here won't match the initial socket assigned at ingress TC, the packets will still fallback to the normal egress path; You're right in that case 2b above will continue with the same restrictions as before. Tiago.