From 33c162a980fe03498fcecb917f618ad7e7c55e61 Mon Sep 17 00:00:00 2001 From: Martin KaFai Lau Date: Mon, 11 Apr 2016 15:29:36 -0700 Subject: [PATCH] ipv6: datagram: Update dst cache of a connected datagram sk during pmtu update There is a case in connected UDP socket such that getsockopt(IPV6_MTU) will return a stale MTU value. The reproducible sequence could be the following: 1. Create a connected UDP socket 2. Send some datagrams out 3. Receive a ICMPV6_PKT_TOOBIG 4. No new outgoing datagrams to trigger the sk_dst_check() logic to update the sk->sk_dst_cache. 5. getsockopt(IPV6_MTU) returns the mtu from the invalid sk->sk_dst_cache instead of the newly created RTF_CACHE clone. This patch updates the sk->sk_dst_cache for a connected datagram sk during pmtu-update code path. Note that the sk->sk_v6_daddr is used to do the route lookup instead of skb->data (i.e. iph). It is because a UDP socket can become connected after sending out some datagrams in un-connected state. or It can be connected multiple times to different destinations. Hence, iph may not be related to where sk is currently connected to. It is done under '!sock_owned_by_user(sk)' condition because the user may make another ip6_datagram_connect() (i.e changing the sk->sk_v6_daddr) while dst lookup is happening in the pmtu-update code path. For the sock_owned_by_user(sk) == true case, the next patch will introduce a release_cb() which will update the sk->sk_dst_cache. Test: Server (Connected UDP Socket): ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Route Details: [root@arch-fb-vm1 ~]# ip -6 r show | egrep '2fac' 2fac::/64 dev eth0 proto kernel metric 256 pref medium 2fac:face::/64 via 2fac::face dev eth0 metric 1024 pref medium A simple python code to create a connected UDP socket: import socket import errno HOST = '2fac::1' PORT = 8080 s = socket.socket(socket.AF_INET6, socket.SOCK_DGRAM) s.bind((HOST, PORT)) s.connect(('2fac:face::face', 53)) print("connected") while True: try: data = s.recv(1024) except socket.error as se: if se.errno == errno.EMSGSIZE: pmtu = s.getsockopt(41, 24) print("PMTU:%d" % pmtu) break s.close() Python program output after getting a ICMPV6_PKT_TOOBIG: [root@arch-fb-vm1 ~]# python2 ~/devshare/kernel/tasks/fib6/udp-connect-53-8080.py connected PMTU:1300 Cache routes after recieving TOOBIG: [root@arch-fb-vm1 ~]# ip -6 r show table cache 2fac:face::face via 2fac::face dev eth0 metric 0 cache expires 463sec mtu 1300 pref medium Client (Send the ICMPV6_PKT_TOOBIG): ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ scapy is used to generate the TOOBIG message. Here is the scapy script I have used: >>> p=Ether(src='da:75:4d:36:ac:32', dst='52:54:00:12:34:66', type=0x86dd)/IPv6(src='2fac::face', dst='2fac::1')/ICMPv6PacketTooBig(mtu=1300)/IPv6(src='2fac:: 1',dst='2fac:face::face', nh='UDP')/UDP(sport=8080,dport=53) >>> sendp(p, iface='qemubr0') Fixes: 45e4fd26683c ("ipv6: Only create RTF_CACHE routes after encountering pmtu exception") Signed-off-by: Martin KaFai Lau Reported-by: Wei Wang Cc: Cong Wang Cc: Eric Dumazet Cc: Wei Wang Signed-off-by: David S. Miller --- include/net/ipv6.h | 1 + net/ipv6/datagram.c | 20 +++++++++++--------- net/ipv6/route.c | 12 ++++++++++++ 3 files changed, 24 insertions(+), 9 deletions(-) diff --git a/include/net/ipv6.h b/include/net/ipv6.h index d0aeb97aec5d..fd02e90b1289 100644 --- a/include/net/ipv6.h +++ b/include/net/ipv6.h @@ -959,6 +959,7 @@ int compat_ipv6_getsockopt(struct sock *sk, int level, int optname, int ip6_datagram_connect(struct sock *sk, struct sockaddr *addr, int addr_len); int ip6_datagram_connect_v6_only(struct sock *sk, struct sockaddr *addr, int addr_len); +int ip6_datagram_dst_update(struct sock *sk, bool fix_sk_saddr); int ipv6_recv_error(struct sock *sk, struct msghdr *msg, int len, int *addr_len); diff --git a/net/ipv6/datagram.c b/net/ipv6/datagram.c index 669585e11294..59e01f27db9f 100644 --- a/net/ipv6/datagram.c +++ b/net/ipv6/datagram.c @@ -64,7 +64,7 @@ static void ip6_datagram_flow_key_init(struct flowi6 *fl6, struct sock *sk) security_sk_classify_flow(sk, flowi6_to_flowi(fl6)); } -static int ip6_datagram_dst_update(struct sock *sk) +int ip6_datagram_dst_update(struct sock *sk, bool fix_sk_saddr) { struct ip6_flowlabel *flowlabel = NULL; struct in6_addr *final_p, final; @@ -93,14 +93,16 @@ static int ip6_datagram_dst_update(struct sock *sk) goto out; } - if (ipv6_addr_any(&np->saddr)) - np->saddr = fl6.saddr; + if (fix_sk_saddr) { + if (ipv6_addr_any(&np->saddr)) + np->saddr = fl6.saddr; - if (ipv6_addr_any(&sk->sk_v6_rcv_saddr)) { - sk->sk_v6_rcv_saddr = fl6.saddr; - inet->inet_rcv_saddr = LOOPBACK4_IPV6; - if (sk->sk_prot->rehash) - sk->sk_prot->rehash(sk); + if (ipv6_addr_any(&sk->sk_v6_rcv_saddr)) { + sk->sk_v6_rcv_saddr = fl6.saddr; + inet->inet_rcv_saddr = LOOPBACK4_IPV6; + if (sk->sk_prot->rehash) + sk->sk_prot->rehash(sk); + } } ip6_dst_store(sk, dst, @@ -221,7 +223,7 @@ ipv4_connected: * destination cache for it. */ - err = ip6_datagram_dst_update(sk); + err = ip6_datagram_dst_update(sk, true); if (err) goto out; diff --git a/net/ipv6/route.c b/net/ipv6/route.c index 1d8871a5ed20..d916d6ab9ad2 100644 --- a/net/ipv6/route.c +++ b/net/ipv6/route.c @@ -1418,8 +1418,20 @@ EXPORT_SYMBOL_GPL(ip6_update_pmtu); void ip6_sk_update_pmtu(struct sk_buff *skb, struct sock *sk, __be32 mtu) { + struct dst_entry *dst; + ip6_update_pmtu(skb, sock_net(sk), mtu, sk->sk_bound_dev_if, sk->sk_mark); + + dst = __sk_dst_get(sk); + if (!dst || !dst->obsolete || + dst->ops->check(dst, inet6_sk(sk)->dst_cookie)) + return; + + bh_lock_sock(sk); + if (!sock_owned_by_user(sk) && !ipv6_addr_v4mapped(&sk->sk_v6_daddr)) + ip6_datagram_dst_update(sk, false); + bh_unlock_sock(sk); } EXPORT_SYMBOL_GPL(ip6_sk_update_pmtu); -- 2.20.1