net: udp: prefer listeners bound to an address

A relatively common use case is to have several IPs configured
on a host, and have different listeners for each of them. We would
like to add a "catch all" listener on addr_any, to match incoming
connections not served by any of the listeners bound to a specific
address.

However, port-only lookups can match addr_any sockets when sockets
listening on specific addresses are present if so_reuseport flag
is set. This patch eliminates lookups into port-only hashtable,
as lookups by (addr,port) tuple are easily available.

In addition, compute_score() is tweaked to _not_ match
addr_any sockets to specific addresses, as hash collisions
could result in the unwanted behavior described above.

Tested: the patch compiles; full test in the last patch in this
patchset. Existing reuseport_* selftests also pass.

Suggested-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: Peter Oskolkov <posk@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c
index aff2a8e..3fb0ed5 100644 (file)
--- a/net/ipv4/udp.c
+++ b/net/ipv4/udp.c
@@ -380,15 +380,12 @@ static int compute_score(struct sock *sk, struct net *net,
            ipv6_only_sock(sk))
                return -1;
 
-       score = (sk->sk_family == PF_INET) ? 2 : 1;
-       inet = inet_sk(sk);
+       if (sk->sk_rcv_saddr != daddr)
+               return -1;
 
-       if (inet->inet_rcv_saddr) {
-               if (inet->inet_rcv_saddr != daddr)
-                       return -1;
-               score += 4;
-       }
+       score = (sk->sk_family == PF_INET) ? 2 : 1;
 
+       inet = inet_sk(sk);
        if (inet->inet_daddr) {
                if (inet->inet_daddr != saddr)
                        return -1;
@@ -464,65 +461,30 @@ struct sock *__udp4_lib_lookup(struct net *net, __be32 saddr,
                __be16 sport, __be32 daddr, __be16 dport, int dif,
                int sdif, struct udp_table *udptable, struct sk_buff *skb)
 {
-       struct sock *sk, *result;
+       struct sock *result;
        unsigned short hnum = ntohs(dport);
-       unsigned int hash2, slot2, slot = udp_hashfn(net, hnum, udptable->mask);
-       struct udp_hslot *hslot2, *hslot = &udptable->hash[slot];
+       unsigned int hash2, slot2;
+       struct udp_hslot *hslot2;
        bool exact_dif = udp_lib_exact_dif_match(net, skb);
-       int score, badness;
-       u32 hash = 0;
 
-       if (hslot->count > 10) {
-               hash2 = ipv4_portaddr_hash(net, daddr, hnum);
+       hash2 = ipv4_portaddr_hash(net, daddr, hnum);
+       slot2 = hash2 & udptable->mask;
+       hslot2 = &udptable->hash2[slot2];
+
+       result = udp4_lib_lookup2(net, saddr, sport,
+                                 daddr, hnum, dif, sdif,
+                                 exact_dif, hslot2, skb);
+       if (!result) {
+               hash2 = ipv4_portaddr_hash(net, htonl(INADDR_ANY), hnum);
                slot2 = hash2 & udptable->mask;
                hslot2 = &udptable->hash2[slot2];
-               if (hslot->count < hslot2->count)
-                       goto begin;
 
                result = udp4_lib_lookup2(net, saddr, sport,
-                                         daddr, hnum, dif, sdif,
+                                         htonl(INADDR_ANY), hnum, dif, sdif,
                                          exact_dif, hslot2, skb);
-               if (!result) {
-                       unsigned int old_slot2 = slot2;
-                       hash2 = ipv4_portaddr_hash(net, htonl(INADDR_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 = udp4_lib_lookup2(net, saddr, sport,
-                                                 daddr, hnum, dif, sdif,
-                                                 exact_dif, hslot2, skb);
-               }
-               if (unlikely(IS_ERR(result)))
-                       return NULL;
-               return result;
-       }
-begin:
-       result = NULL;
-       badness = 0;
-       sk_for_each_rcu(sk, &hslot->head) {
-               score = compute_score(sk, net, saddr, sport,
-                                     daddr, hnum, dif, sdif, exact_dif);
-               if (score > badness) {
-                       if (sk->sk_reuseport) {
-                               hash = udp_ehashfn(net, daddr, hnum,
-                                                  saddr, sport);
-                               result = reuseport_select_sock(sk, hash, skb,
-                                                       sizeof(struct udphdr));
-                               if (unlikely(IS_ERR(result)))
-                                       return NULL;
-                               if (result)
-                                       return result;
-                       }
-                       result = sk;
-                       badness = score;
-               }
        }
+       if (unlikely(IS_ERR(result)))
+               return NULL;
        return result;
 }
 EXPORT_SYMBOL_GPL(__udp4_lib_lookup);