udp: add rehash on connect()

commit 30fff923 introduced in linux-2.6.33 (udp: bind() optimisation)
added a secondary hash on UDP, hashed on (local addr, local port).

Problem is that following sequence :

fd = socket(...)
connect(fd, &remote, ...)

not only selects remote end point (address and port), but also sets
local address, while UDP stack stored in secondary hash table the socket
while its local address was INADDR_ANY (or ipv6 equivalent)

Sequence is :
 - autobind() : choose a random local port, insert socket in hash tables
              [while local address is INADDR_ANY]
 - connect() : set remote address and port, change local address to IP
              given by a route lookup.

When an incoming UDP frame comes, if more than 10 sockets are found in
primary hash table, we switch to secondary table, and fail to find
socket because its local address changed.

One solution to this problem is to rehash datagram socket if needed.

We add a new rehash(struct socket *) method in "struct proto", and
implement this method for UDP v4 & v6, using a common helper.

This rehashing only takes care of secondary hash table, since primary
hash (based on local port only) is not changed.

Reported-by: Krzysztof Piotr Oledzki <ole@ans.pl>
Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Tested-by: Krzysztof Piotr Oledzki <ole@ans.pl>
Signed-off-by: David S. Miller <davem@davemloft.net>

2 files changed, 16 insertions, 1 deletions

diff --git a/net/ipv6/datagram.c b/net/ipv6/datagram.c
index 7d929a22cbc2..ef371aa01ac5 100644
--- a/net/ipv6/datagram.c
+++ b/net/ipv6/datagram.c
@@ -105,9 +105,12 @@ ipv4_connected:
                 if (ipv6_addr_any(&np->saddr))
                         ipv6_addr_set_v4mapped(inet->inet_saddr, &np->saddr);
 
-                if (ipv6_addr_any(&np->rcv_saddr))
+                if (ipv6_addr_any(&np->rcv_saddr)) {
                         ipv6_addr_set_v4mapped(inet->inet_rcv_saddr,
                                                &np->rcv_saddr);
+                        if (sk->sk_prot->rehash)
+                                sk->sk_prot->rehash(sk);
+                }
 
                 goto out;
         }
@@ -181,6 +184,8 @@ ipv4_connected:
         if (ipv6_addr_any(&np->rcv_saddr)) {
                 ipv6_addr_copy(&np->rcv_saddr, &fl.fl6_src);
                 inet->inet_rcv_saddr = LOOPBACK4_IPV6;
+                if (sk->sk_prot->rehash)
+                        sk->sk_prot->rehash(sk);
         }
 
         ip6_dst_store(sk, dst,
diff --git a/net/ipv6/udp.c b/net/ipv6/udp.c
index 1dd1affdead2..5acb3560ff15 100644
--- a/net/ipv6/udp.c
+++ b/net/ipv6/udp.c
@@ -111,6 +111,15 @@ int udp_v6_get_port(struct sock *sk, unsigned short snum)
         return udp_lib_get_port(sk, snum, ipv6_rcv_saddr_equal, hash2_nulladdr);
 }
 
+static void udp_v6_rehash(struct sock *sk)
+{
+        u16 new_hash = udp6_portaddr_hash(sock_net(sk),
+                                          &inet6_sk(sk)->rcv_saddr,
+                                          inet_sk(sk)->inet_num);
+
+        udp_lib_rehash(sk, new_hash);
+}
+
 static inline int compute_score(struct sock *sk, struct net *net,
                                 unsigned short hnum,
                                 struct in6_addr *saddr, __be16 sport,
@@ -1447,6 +1456,7 @@ struct proto udpv6_prot = {
         .backlog_rcv       = udpv6_queue_rcv_skb,
         .hash              = udp_lib_hash,
         .unhash            = udp_lib_unhash,
+        .rehash            = udp_v6_rehash,
         .get_port          = udp_v6_get_port,
         .memory_allocated  = &udp_memory_allocated,
         .sysctl_mem        = sysctl_udp_mem,