git: 29a062108405 - main - tcp: allow connections to IPv6 anycast address

The branch main has been updated by ivy:

URL: https://cgit.FreeBSD.org/src/commit/?id=29a062108405cf97e16d9a82635ddc9cfd89ae06

commit 29a062108405cf97e16d9a82635ddc9cfd89ae06
Author:     Lexi Winter <ivy@FreeBSD.org>
AuthorDate: 2025-05-19 12:33:45 +0000
Commit:     Lexi Winter <ivy@FreeBSD.org>
CommitDate: 2025-05-19 12:40:26 +0000

    tcp: allow connections to IPv6 anycast address
    
    currently, we reject incoming TCP connections to an IPv6 anycast address
    based on IETF I-D "draft-itojun-ipv6-tcp-to-anycast-01"[0].  the
    rationale is that since RFC2373 prohibits sending IPv6 packets with an
    anycast address as the source address, it would be impossible to
    establish a TCP connection to such an address since the destination host
    could not send any replies.
    
    however, this restriction was lifted in RFC4291 and it is no longer
    forbidden to send packets from an anycast address; therefore, it's both
    possible and permitted to establish a TCP connection using an anycast
    address as src or dst address (or both).
    
    based on the above, delete this restriction and allow people to do this.
    
    while there are certain operational reasons to avoid TCP anycast (such
    as the risk of the route changing while the connection is open), these
    also apply to IPv4 anycast and are specific to the local environment;
    for example, it's perfectly valid to have an anycast address which is
    only ever assigned to one node.
    
    [0] https://www.ietf.org/archive/id/draft-itojun-ipv6-tcp-to-anycast-01.txt
    
    Reviewed by:    tuexen, kevans, adrian
    Approved by:    kevans (mentor), des (mentor)
    Differential Revision:  https://reviews.freebsd.org/D50019
---
 sys/netinet/tcp_input.c | 15 ---------------
 1 file changed, 15 deletions(-)

diff --git a/sys/netinet/tcp_input.c b/sys/netinet/tcp_input.c
index 817079dfe6c8..c00a102e8520 100644
--- a/sys/netinet/tcp_input.c
+++ b/sys/netinet/tcp_input.c
@@ -567,8 +567,6 @@ int
 tcp6_input_with_port(struct mbuf **mp, int *offp, int proto, uint16_t port)
 {
 	struct mbuf *m;
-	struct in6_ifaddr *ia6;
-	struct ip6_hdr *ip6;
 
 	m = *mp;
 	if (m->m_len < *offp + sizeof(struct tcphdr)) {
@@ -580,19 +578,6 @@ tcp6_input_with_port(struct mbuf **mp, int *offp, int proto, uint16_t port)
 		}
 	}
 
-	/*
-	 * draft-itojun-ipv6-tcp-to-anycast
-	 * better place to put this in?
-	 */
-	ip6 = mtod(m, struct ip6_hdr *);
-	ia6 = in6ifa_ifwithaddr(&ip6->ip6_dst, 0 /* XXX */, false);
-	if (ia6 && (ia6->ia6_flags & IN6_IFF_ANYCAST)) {
-		icmp6_error(m, ICMP6_DST_UNREACH, ICMP6_DST_UNREACH_ADDR,
-			    (caddr_t)&ip6->ip6_dst - (caddr_t)ip6);
-		*mp = NULL;
-		return (IPPROTO_DONE);
-	}
-
 	*mp = m;
 	return (tcp_input_with_port(mp, offp, proto, port));
 }