From: Willem de Bruijn <willemb@google.com>
Date: Wed, 2 Nov 2016 15:02:17 +0000 (-0400)
Subject: ipv6: add IPV6_RECVFRAGSIZE cmsg
X-Git-Url: http://git.lede-project.org./?a=commitdiff_plain;h=0cc0aa614b4c24b21b2492c0a1753035ee8c6edb;p=openwrt%2Fstaging%2Fblogic.git

ipv6: add IPV6_RECVFRAGSIZE cmsg

When reading a datagram or raw packet that arrived fragmented, expose
the maximum fragment size if recorded to allow applications to
estimate receive path MTU.

At this point, the field is only recorded when ipv6 connection
tracking is enabled. A follow-up patch will record this field also
in the ipv6 input path.

Tested using the test for IP_RECVFRAGSIZE plus

  ip netns exec to ip addr add dev veth1 fc07::1/64
  ip netns exec from ip addr add dev veth0 fc07::2/64

  ip netns exec to ./recv_cmsg_recvfragsize -6 -u -p 6000 &
  ip netns exec from nc -q 1 -u fc07::1 6000 < payload

Both with and without enabling connection tracking

  ip6tables -A INPUT -m state --state NEW -p udp -j LOG

Signed-off-by: Willem de Bruijn <willemb@google.com>
Acked-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
---

diff --git a/include/linux/ipv6.h b/include/linux/ipv6.h
index ca1ad9ebbc92..1afb6e8d35c3 100644
--- a/include/linux/ipv6.h
+++ b/include/linux/ipv6.h
@@ -229,8 +229,9 @@ struct ipv6_pinfo {
                                 rxflow:1,
 				rxtclass:1,
 				rxpmtu:1,
-				rxorigdstaddr:1;
-				/* 2 bits hole */
+				rxorigdstaddr:1,
+				recvfragsize:1;
+				/* 1 bits hole */
 		} bits;
 		__u16		all;
 	} rxopt;
diff --git a/include/uapi/linux/in6.h b/include/uapi/linux/in6.h
index b39ea4f2e701..46444f8fbee4 100644
--- a/include/uapi/linux/in6.h
+++ b/include/uapi/linux/in6.h
@@ -283,6 +283,7 @@ struct in6_flowlabel_req {
 #define IPV6_RECVORIGDSTADDR    IPV6_ORIGDSTADDR
 #define IPV6_TRANSPARENT        75
 #define IPV6_UNICAST_IF         76
+#define IPV6_RECVFRAGSIZE	77
 
 /*
  * Multicast Routing:
diff --git a/net/ipv6/datagram.c b/net/ipv6/datagram.c
index 37874e2f30ed..620c79a0130a 100644
--- a/net/ipv6/datagram.c
+++ b/net/ipv6/datagram.c
@@ -715,6 +715,11 @@ void ip6_datagram_recv_specific_ctl(struct sock *sk, struct msghdr *msg,
 			put_cmsg(msg, SOL_IPV6, IPV6_ORIGDSTADDR, sizeof(sin6), &sin6);
 		}
 	}
+	if (np->rxopt.bits.recvfragsize && opt->frag_max_size) {
+		int val = opt->frag_max_size;
+
+		put_cmsg(msg, SOL_IPV6, IPV6_RECVFRAGSIZE, sizeof(val), &val);
+	}
 }
 
 void ip6_datagram_recv_ctl(struct sock *sk, struct msghdr *msg,
diff --git a/net/ipv6/ipv6_sockglue.c b/net/ipv6/ipv6_sockglue.c
index 636ec56f5f50..6c126780fcf2 100644
--- a/net/ipv6/ipv6_sockglue.c
+++ b/net/ipv6/ipv6_sockglue.c
@@ -868,6 +868,10 @@ pref_skip_coa:
 		np->autoflowlabel = valbool;
 		retv = 0;
 		break;
+	case IPV6_RECVFRAGSIZE:
+		np->rxopt.bits.recvfragsize = valbool;
+		retv = 0;
+		break;
 	}
 
 	release_sock(sk);
@@ -1310,6 +1314,10 @@ static int do_ipv6_getsockopt(struct sock *sk, int level, int optname,
 		val = np->autoflowlabel;
 		break;
 
+	case IPV6_RECVFRAGSIZE:
+		val = np->rxopt.bits.recvfragsize;
+		break;
+
 	default:
 		return -ENOPROTOOPT;
 	}