udp reuseport: fix packet of same flow hashed to different socket

There is a corner case in which udp packets belonging to a same
flow are hashed to different socket when hslot->count changes from 10
to 11:

1) When hslot->count <= 10, __udp_lib_lookup() searches udp_table->hash,
and always passes 'daddr' to udp_ehashfn().

2) When hslot->count > 10, __udp_lib_lookup() searches udp_table->hash2,
but may pass 'INADDR_ANY' to udp_ehashfn() if the sockets are bound to
INADDR_ANY instead of some specific addr.

That means when hslot->count changes from 10 to 11, the hash calculated by
udp_ehashfn() is also changed, and the udp packets belonging to a same
flow will be hashed to different socket.

This is easily reproduced:
1) Create 10 udp sockets and bind all of them to 0.0.0.0:40000.
2) From the same host send udp packets to 127.0.0.1:40000, record the
socket index which receives the packets.
3) Create 1 more udp socket and bind it to 0.0.0.0:44096. The number 44096
is 40000 + UDP_HASH_SIZE(4096), this makes the new socket put into the
same hslot as the aformentioned 10 sockets, and makes the hslot->count
change from 10 to 11.
4) From the same host send udp packets to 127.0.0.1:40000, and the socket
index which receives the packets will be different from the one received
in step 2.
This should not happen as the socket bound to 0.0.0.0:44096 should not
change the behavior of the sockets bound to 0.0.0.0:40000.

It's the same case for IPv6, and this patch also fixes that.

Signed-off-by: Su, Xuemin <suxm@chinanetcenter.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 16 insertions, 55 deletions

diff --git a/net/ipv6/udp.c b/net/ipv6/udp.c
index f421c9f23c5b..005dc82c2138 100644
--- a/net/ipv6/udp.c
+++ b/net/ipv6/udp.c
@@ -115,11 +115,10 @@ static void udp_v6_rehash(struct sock *sk)
         udp_lib_rehash(sk, new_hash);
 }
 
-static inline int compute_score(struct sock *sk, struct net *net,
-                                unsigned short hnum,
-                                const struct in6_addr *saddr, __be16 sport,
-                                const struct in6_addr *daddr, __be16 dport,
-                                int dif)
+static int compute_score(struct sock *sk, struct net *net,
+                         const struct in6_addr *saddr, __be16 sport,
+                         const struct in6_addr *daddr, unsigned short hnum,
+                         int dif)
 {
         int score;
         struct inet_sock *inet;
@@ -162,54 +161,11 @@ static inline int compute_score(struct sock *sk, struct net *net,
         return score;
 }
 
-static inline int compute_score2(struct sock *sk, struct net *net,
-                                 const struct in6_addr *saddr, __be16 sport,
-                                 const struct in6_addr *daddr,
-                                 unsigned short hnum, int dif)
-{
-        int score;
-        struct inet_sock *inet;
-
-        if (!net_eq(sock_net(sk), net) ||
-            udp_sk(sk)->udp_port_hash != hnum ||
-            sk->sk_family != PF_INET6)
-                return -1;
-
-        if (!ipv6_addr_equal(&sk->sk_v6_rcv_saddr, daddr))
-                return -1;
-
-        score = 0;
-        inet = inet_sk(sk);
-
-        if (inet->inet_dport) {
-                if (inet->inet_dport != sport)
-                        return -1;
-                score++;
-        }
-
-        if (!ipv6_addr_any(&sk->sk_v6_daddr)) {
-                if (!ipv6_addr_equal(&sk->sk_v6_daddr, saddr))
-                        return -1;
-                score++;
-        }
-
-        if (sk->sk_bound_dev_if) {
-                if (sk->sk_bound_dev_if != dif)
-                        return -1;
-                score++;
-        }
-
-        if (sk->sk_incoming_cpu == raw_smp_processor_id())
-                score++;
-
-        return score;
-}
-
-/* called with read_rcu_lock() */
+/* called with rcu_read_lock() */
 static struct sock *udp6_lib_lookup2(struct net *net,
                 const struct in6_addr *saddr, __be16 sport,
                 const struct in6_addr *daddr, unsigned int hnum, int dif,
-                struct udp_hslot *hslot2, unsigned int slot2,
+                struct udp_hslot *hslot2,
                 struct sk_buff *skb)
 {
         struct sock *sk, *result;
@@ -219,7 +175,7 @@ static struct sock *udp6_lib_lookup2(struct net *net,
         result = NULL;
         badness = -1;
         udp_portaddr_for_each_entry_rcu(sk, &hslot2->head) {
-                score = compute_score2(sk, net, saddr, sport,
+                score = compute_score(sk, net, saddr, sport,
                                       daddr, hnum, dif);
                 if (score > badness) {
                         reuseport = sk->sk_reuseport;
@@ -268,17 +224,22 @@ struct sock *__udp6_lib_lookup(struct net *net,
 
                 result = udp6_lib_lookup2(net, saddr, sport,
                                           daddr, hnum, dif,
-                                          hslot2, slot2, skb);
+                                          hslot2, skb);
                 if (!result) {
+                        unsigned int old_slot2 = slot2;
                         hash2 = udp6_portaddr_hash(net, &in6addr_any, hnum);
                         slot2 = hash2 & udptable->mask;
+                        /* avoid searching the same slot again. */
+                        if (unlikely(slot2 == old_slot2))
+                                return result;
+
                         hslot2 = &udptable->hash2[slot2];
                         if (hslot->count < hslot2->count)
                                 goto begin;
 
                         result = udp6_lib_lookup2(net, saddr, sport,
-                                                  &in6addr_any, hnum, dif,
-                                                  hslot2, slot2, skb);
+                                                  daddr, hnum, dif,
+                                                  hslot2, skb);
                 }
                 return result;
         }
@@ -286,7 +247,7 @@ begin:
         result = NULL;
         badness = -1;
         sk_for_each_rcu(sk, &hslot->head) {
-                score = compute_score(sk, net, hnum, saddr, sport, daddr, dport, dif);
+                score = compute_score(sk, net, saddr, sport, daddr, hnum, dif);
                 if (score > badness) {
                         reuseport = sk->sk_reuseport;
                         if (reuseport) {