Merge branch 'ip-recvfragsize-cmsg'

Willem de Bruijn says:

====================
ip: add RECVFRAGSIZE cmsg

On IP datagrams and raw sockets, when packets arrive fragmented,
expose the largest received fragment size through a new cmsg.

Protocols implemented on top of these sockets may use this, for
instance, to inform peers to lower MSS on platforms that silently
allow send calls to exceed PMTU and cause fragmentation.
====================

Signed-off-by: David S. Miller <davem@davemloft.net>

8 files changed, 51 insertions, 3 deletions

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/net/inet_sock.h b/include/net/inet_sock.h
index 236a81034fef..c9cff977a7fb 100644
--- a/include/net/inet_sock.h
+++ b/include/net/inet_sock.h
@@ -228,6 +228,7 @@ struct inet_sock {
 #define IP_CMSG_PASSSEC		BIT(5)
 #define IP_CMSG_ORIGDSTADDR	BIT(6)
 #define IP_CMSG_CHECKSUM	BIT(7)
+#define IP_CMSG_RECVFRAGSIZE	BIT(8)
 
 /**
  * sk_to_full_sk - Access to a full socket
diff --git a/include/uapi/linux/in.h b/include/uapi/linux/in.h
index eaf94919291a..4e557f4e9553 100644
--- a/include/uapi/linux/in.h
+++ b/include/uapi/linux/in.h
@@ -117,6 +117,7 @@ struct in_addr {
 #define IP_NODEFRAG     22
 #define IP_CHECKSUM	23
 #define IP_BIND_ADDRESS_NO_PORT	24
+#define IP_RECVFRAGSIZE	25
 
 /* IP_MTU_DISCOVER values */
 #define IP_PMTUDISC_DONT		0	/* Never send DF frames */
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/ipv4/ip_sockglue.c b/net/ipv4/ip_sockglue.c
index b8a2d63d1fb8..ecbaae200131 100644
--- a/net/ipv4/ip_sockglue.c
+++ b/net/ipv4/ip_sockglue.c
@@ -97,6 +97,17 @@ static void ip_cmsg_recv_retopts(struct msghdr *msg, struct sk_buff *skb)
 	put_cmsg(msg, SOL_IP, IP_RETOPTS, opt->optlen, opt->__data);
 }
 
+static void ip_cmsg_recv_fragsize(struct msghdr *msg, struct sk_buff *skb)
+{
+	int val;
+
+	if (IPCB(skb)->frag_max_size == 0)
+		return;
+
+	val = IPCB(skb)->frag_max_size;
+	put_cmsg(msg, SOL_IP, IP_RECVFRAGSIZE, sizeof(val), &val);
+}
+
 static void ip_cmsg_recv_checksum(struct msghdr *msg, struct sk_buff *skb,
 				  int tlen, int offset)
 {
@@ -218,6 +229,9 @@ void ip_cmsg_recv_offset(struct msghdr *msg, struct sk_buff *skb,
 
 	if (flags & IP_CMSG_CHECKSUM)
 		ip_cmsg_recv_checksum(msg, skb, tlen, offset);
+
+	if (flags & IP_CMSG_RECVFRAGSIZE)
+		ip_cmsg_recv_fragsize(msg, skb);
 }
 EXPORT_SYMBOL(ip_cmsg_recv_offset);
 
@@ -614,6 +628,7 @@ static int do_ip_setsockopt(struct sock *sk, int level,
 	case IP_MULTICAST_LOOP:
 	case IP_RECVORIGDSTADDR:
 	case IP_CHECKSUM:
+	case IP_RECVFRAGSIZE:
 		if (optlen >= sizeof(int)) {
 			if (get_user(val, (int __user *) optval))
 				return -EFAULT;
@@ -726,6 +741,14 @@ static int do_ip_setsockopt(struct sock *sk, int level,
 			}
 		}
 		break;
+	case IP_RECVFRAGSIZE:
+		if (sk->sk_type != SOCK_RAW && sk->sk_type != SOCK_DGRAM)
+			goto e_inval;
+		if (val)
+			inet->cmsg_flags |= IP_CMSG_RECVFRAGSIZE;
+		else
+			inet->cmsg_flags &= ~IP_CMSG_RECVFRAGSIZE;
+		break;
 	case IP_TOS:	/* This sets both TOS and Precedence */
 		if (sk->sk_type == SOCK_STREAM) {
 			val &= ~INET_ECN_MASK;
@@ -1357,6 +1380,9 @@ static int do_ip_getsockopt(struct sock *sk, int level, int optname,
 	case IP_CHECKSUM:
 		val = (inet->cmsg_flags & IP_CMSG_CHECKSUM) != 0;
 		break;
+	case IP_RECVFRAGSIZE:
+		val = (inet->cmsg_flags & IP_CMSG_RECVFRAGSIZE) != 0;
+		break;
 	case IP_TOS:
 		val = inet->tos;
 		break;
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;
 	}
diff --git a/net/ipv6/reassembly.c b/net/ipv6/reassembly.c
index 3815e8505ed2..e1da5b888cc4 100644
--- a/net/ipv6/reassembly.c
+++ b/net/ipv6/reassembly.c
@@ -211,7 +211,7 @@ static int ip6_frag_queue(struct frag_queue *fq, struct sk_buff *skb,
 {
 	struct sk_buff *prev, *next;
 	struct net_device *dev;
-	int offset, end;
+	int offset, end, fragsize;
 	struct net *net = dev_net(skb_dst(skb)->dev);
 	u8 ecn;
 
@@ -336,6 +336,10 @@ found:
 	fq->ecn |= ecn;
 	add_frag_mem_limit(fq->q.net, skb->truesize);
 
+	fragsize = -skb_network_offset(skb) + skb->len;
+	if (fragsize > fq->q.max_size)
+		fq->q.max_size = fragsize;
+
 	/* The first fragment.
 	 * nhoffset is obtained from the first fragment, of course.
 	 */
@@ -495,6 +499,7 @@ static int ip6_frag_reasm(struct frag_queue *fq, struct sk_buff *prev,
 	ipv6_change_dsfield(ipv6_hdr(head), 0xff, ecn);
 	IP6CB(head)->nhoff = nhoff;
 	IP6CB(head)->flags |= IP6SKB_FRAGMENTED;
+	IP6CB(head)->frag_max_size = fq->q.max_size;
 
 	/* Yes, and fold redundant checksum back. 8) */
 	skb_postpush_rcsum(head, skb_network_header(head),