ipv6: drop feature RTAX_FEATURE_ALLFRAG

RTAX_FEATURE_ALLFRAG was added before the first git commit:

https://www.mail-archive.com/bk-commits-head@vger.kernel.org/msg03399.html

The feature would send packets to the fragmentation path if a box
receives a PMTU value with less than 1280 byte. However, since commit
9d289715eb5c ("ipv6: stop sending PTB packets for MTU < 1280"), such
message would be simply discarded. The feature flag is neither supported
in iproute2 utility. In theory one can still manipulate it with direct
netlink message, but it is not ideal because it was based on obsoleted
guidance of RFC-2460 (replaced by RFC-8200).

The feature would always test false at the moment, so remove related
code or mark them as unused.

Signed-off-by: Yan Zhai <yan@cloudflare.com>
Reviewed-by: Florian Westphal <fw@strlen.de>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Link: https://lore.kernel.org/r/d78e44dcd9968a252143ffe78460446476a472a1.1698156966.git.yan@cloudflare.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

5 files changed, 4 insertions, 35 deletions

diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index 2866ccbccde0..ca4d7594efd4 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -1698,14 +1698,6 @@ static inline int __tcp_mtu_to_mss(struct sock *sk, int pmtu)
 	 */
 	mss_now = pmtu - icsk->icsk_af_ops->net_header_len - sizeof(struct tcphdr);
 
-	/* IPv6 adds a frag_hdr in case RTAX_FEATURE_ALLFRAG is set */
-	if (icsk->icsk_af_ops->net_frag_header_len) {
-		const struct dst_entry *dst = __sk_dst_get(sk);
-
-		if (dst && dst_allfrag(dst))
-			mss_now -= icsk->icsk_af_ops->net_frag_header_len;
-	}
-
 	/* Clamp it (mss_clamp does not include tcp options) */
 	if (mss_now > tp->rx_opt.mss_clamp)
 		mss_now = tp->rx_opt.mss_clamp;
@@ -1733,21 +1725,11 @@ int tcp_mss_to_mtu(struct sock *sk, int mss)
 {
 	const struct tcp_sock *tp = tcp_sk(sk);
 	const struct inet_connection_sock *icsk = inet_csk(sk);
-	int mtu;
 
-	mtu = mss +
+	return mss +
 	      tp->tcp_header_len +
 	      icsk->icsk_ext_hdr_len +
 	      icsk->icsk_af_ops->net_header_len;
-
-	/* IPv6 adds a frag_hdr in case RTAX_FEATURE_ALLFRAG is set */
-	if (icsk->icsk_af_ops->net_frag_header_len) {
-		const struct dst_entry *dst = __sk_dst_get(sk);
-
-		if (dst && dst_allfrag(dst))
-			mtu += icsk->icsk_af_ops->net_frag_header_len;
-	}
-	return mtu;
 }
 EXPORT_SYMBOL(tcp_mss_to_mtu);
 
diff --git a/net/ipv6/ip6_output.c b/net/ipv6/ip6_output.c
index 3c7de89d6755..86efd901ee5a 100644
--- a/net/ipv6/ip6_output.c
+++ b/net/ipv6/ip6_output.c
@@ -191,7 +191,6 @@ static int __ip6_finish_output(struct net *net, struct sock *sk, struct sk_buff
 		return ip6_finish_output_gso_slowpath_drop(net, sk, skb, mtu);
 
 	if ((skb->len > mtu && !skb_is_gso(skb)) ||
-	    dst_allfrag(skb_dst(skb)) ||
 	    (IP6CB(skb)->frag_max_size && skb->len > IP6CB(skb)->frag_max_size))
 		return ip6_fragment(net, sk, skb, ip6_finish_output2);
 	else
@@ -1017,9 +1016,6 @@ slow_path:
 	return err;
 
 fail_toobig:
-	if (skb->sk && dst_allfrag(skb_dst(skb)))
-		sk_gso_disable(skb->sk);
-
 	icmpv6_send(skb, ICMPV6_PKT_TOOBIG, 0, mtu);
 	err = -EMSGSIZE;
 
@@ -1384,10 +1380,7 @@ static int ip6_setup_cork(struct sock *sk, struct inet_cork_full *cork,
 	cork->base.mark = ipc6->sockc.mark;
 	sock_tx_timestamp(sk, ipc6->sockc.tsflags, &cork->base.tx_flags);
 
-	if (dst_allfrag(xfrm_dst_path(&rt->dst)))
-		cork->base.flags |= IPCORK_ALLFRAG;
 	cork->base.length = 0;
-
 	cork->base.transmit_time = ipc6->sockc.transmit_time;
 
 	return 0;
@@ -1444,8 +1437,6 @@ static int __ip6_append_data(struct sock *sk,
 
 	headersize = sizeof(struct ipv6hdr) +
 		     (opt ? opt->opt_flen + opt->opt_nflen : 0) +
-		     (dst_allfrag(&rt->dst) ?
-		      sizeof(struct frag_hdr) : 0) +
 		     rt->rt6i_nfheader_len;
 
 	if (mtu <= fragheaderlen ||
@@ -1555,7 +1546,7 @@ emsgsize:
 
 	while (length > 0) {
 		/* Check if the remaining data fits into current packet. */
-		copy = (cork->length <= mtu && !(cork->flags & IPCORK_ALLFRAG) ? mtu : maxfraglen) - skb->len;
+		copy = (cork->length <= mtu ? mtu : maxfraglen) - skb->len;
 		if (copy < length)
 			copy = maxfraglen - skb->len;
 
@@ -1586,7 +1577,7 @@ alloc_new_skb:
 			 */
 			datalen = length + fraggap;
 
-			if (datalen > (cork->length <= mtu && !(cork->flags & IPCORK_ALLFRAG) ? mtu : maxfraglen) - fragheaderlen)
+			if (datalen > (cork->length <= mtu ? mtu : maxfraglen) - fragheaderlen)
 				datalen = maxfraglen - fragheaderlen - rt->dst.trailer_len;
 			fraglen = datalen + fragheaderlen;
 			pagedlen = 0;
@@ -1835,7 +1826,6 @@ static void ip6_cork_steal_dst(struct sk_buff *skb, struct inet_cork_full *cork)
 	struct dst_entry *dst = cork->base.dst;
 
 	cork->base.dst = NULL;
-	cork->base.flags &= ~IPCORK_ALLFRAG;
 	skb_dst_set(skb, dst);
 }
 
@@ -1856,7 +1846,6 @@ static void ip6_cork_release(struct inet_cork_full *cork,
 	if (cork->base.dst) {
 		dst_release(cork->base.dst);
 		cork->base.dst = NULL;
-		cork->base.flags &= ~IPCORK_ALLFRAG;
 	}
 }
 
diff --git a/net/ipv6/tcp_ipv6.c b/net/ipv6/tcp_ipv6.c
index 0c8a14ba104f..dc27988512a6 100644
--- a/net/ipv6/tcp_ipv6.c
+++ b/net/ipv6/tcp_ipv6.c
@@ -1895,7 +1895,6 @@ const struct inet_connection_sock_af_ops ipv6_specific = {
 	.conn_request	   = tcp_v6_conn_request,
 	.syn_recv_sock	   = tcp_v6_syn_recv_sock,
 	.net_header_len	   = sizeof(struct ipv6hdr),
-	.net_frag_header_len = sizeof(struct frag_hdr),
 	.setsockopt	   = ipv6_setsockopt,
 	.getsockopt	   = ipv6_getsockopt,
 	.addr2sockaddr	   = inet6_csk_addr2sockaddr,
diff --git a/net/ipv6/xfrm6_output.c b/net/ipv6/xfrm6_output.c
index ad07904642ca..5f7b1fdbffe6 100644
--- a/net/ipv6/xfrm6_output.c
+++ b/net/ipv6/xfrm6_output.c
@@ -95,7 +95,7 @@ static int __xfrm6_output(struct net *net, struct sock *sk, struct sk_buff *skb)
 		return -EMSGSIZE;
 	}
 
-	if (toobig || dst_allfrag(skb_dst(skb)))
+	if (toobig)
 		return ip6_fragment(net, sk, skb,
 				    __xfrm6_output_finish);
 
diff --git a/net/mptcp/subflow.c b/net/mptcp/subflow.c
index 2b43577f952e..e120e9616454 100644
--- a/net/mptcp/subflow.c
+++ b/net/mptcp/subflow.c
@@ -2051,7 +2051,6 @@ void __init mptcp_subflow_init(void)
 	subflow_v6m_specific.send_check = ipv4_specific.send_check;
 	subflow_v6m_specific.net_header_len = ipv4_specific.net_header_len;
 	subflow_v6m_specific.mtu_reduced = ipv4_specific.mtu_reduced;
-	subflow_v6m_specific.net_frag_header_len = 0;
 	subflow_v6m_specific.rebuild_header = subflow_rebuild_header;
 
 	tcpv6_prot_override = tcpv6_prot;