udp: fix potential infinite loop in SO_REUSEPORT logic

edumazet · davem330 · commit ed0dfffd7dcd · 2016-01-19T13:52:25.000-05:00
Using a combination of connected and un-connected sockets, Dmitry was able to trigger soft lockups with his fuzzer. The problem is that sockets in the SO_REUSEPORT array might have different scores. Right after sk2=socket(), setsockopt(sk2,...,SO_REUSEPORT, on) and bind(sk2, ...), but _before_ the connect(sk2) is done, sk2 is added into the soreuseport array, with a score which is smaller than the score of first socket sk1 found in hash table (I am speaking of the regular UDP hash table), if sk1 had the connect() done, giving a +8 to its score. hash bucket [X] -> sk1 -> sk2 -> NULL sk1 score = 14 (because it did a connect()) sk2 score = 6 SO_REUSEPORT fast selection is an optimization. If it turns out the score of the selected socket does not match score of first socket, just fallback to old SO_REUSEPORT logic instead of trying to be too smart. Normal SO_REUSEPORT users do not mix different kind of sockets, as this mechanism is used for load balance traffic. Fixes: e32ea7e ("soreuseport: fast reuseport UDP socket selection") Reported-by: Dmitry Vyukov <dvyukov@google.com> Signed-off-by: Eric Dumazet <edumazet@google.com> Cc: Craig Gallek <kraigatgoog@gmail.com> Acked-by: Craig Gallek <kraig@google.com> Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c
@@ -499,6 +499,7 @@ static struct sock *udp4_lib_lookup2(struct net *net,
 	struct sock *sk, *result;
 	struct hlist_nulls_node *node;
 	int score, badness, matches = 0, reuseport = 0;
+	bool select_ok = true;
 	u32 hash = 0;
 
 begin:
@@ -512,14 +513,18 @@ static struct sock *udp4_lib_lookup2(struct net *net,
 			badness = score;
 			reuseport = sk->sk_reuseport;
 			if (reuseport) {
-				struct sock *sk2;
 				hash = udp_ehashfn(net, daddr, hnum,
 						   saddr, sport);
-				sk2 = reuseport_select_sock(sk, hash, skb,
-							    sizeof(struct udphdr));
-				if (sk2) {
-					result = sk2;
-					goto found;
+				if (select_ok) {
+					struct sock *sk2;
+
+					sk2 = reuseport_select_sock(sk, hash, skb,
+							sizeof(struct udphdr));
+					if (sk2) {
+						result = sk2;
+						select_ok = false;
+						goto found;
+					}
 				}
 				matches = 1;
 			}
@@ -563,6 +568,7 @@ struct sock *__udp4_lib_lookup(struct net *net, __be32 saddr,
 	unsigned int hash2, slot2, slot = udp_hashfn(net, hnum, udptable->mask);
 	struct udp_hslot *hslot2, *hslot = &udptable->hash[slot];
 	int score, badness, matches = 0, reuseport = 0;
+	bool select_ok = true;
 	u32 hash = 0;
 
 	rcu_read_lock();
@@ -601,14 +607,18 @@ struct sock *__udp4_lib_lookup(struct net *net, __be32 saddr,
 			badness = score;
 			reuseport = sk->sk_reuseport;
 			if (reuseport) {
-				struct sock *sk2;
 				hash = udp_ehashfn(net, daddr, hnum,
 						   saddr, sport);
-				sk2 = reuseport_select_sock(sk, hash, skb,
+				if (select_ok) {
+					struct sock *sk2;
+
+					sk2 = reuseport_select_sock(sk, hash, skb,
 							sizeof(struct udphdr));
-				if (sk2) {
-					result = sk2;
-					goto found;
+					if (sk2) {
+						result = sk2;
+						select_ok = false;
+						goto found;
+					}
 				}
 				matches = 1;
 			}
diff --git a/net/ipv6/udp.c b/net/ipv6/udp.c
@@ -257,6 +257,7 @@ static struct sock *udp6_lib_lookup2(struct net *net,
 	struct sock *sk, *result;
 	struct hlist_nulls_node *node;
 	int score, badness, matches = 0, reuseport = 0;
+	bool select_ok = true;
 	u32 hash = 0;
 
 begin:
@@ -270,14 +271,18 @@ static struct sock *udp6_lib_lookup2(struct net *net,
 			badness = score;
 			reuseport = sk->sk_reuseport;
 			if (reuseport) {
-				struct sock *sk2;
 				hash = udp6_ehashfn(net, daddr, hnum,
 						    saddr, sport);
-				sk2 = reuseport_select_sock(sk, hash, skb,
-							    sizeof(struct udphdr));
-				if (sk2) {
-					result = sk2;
-					goto found;
+				if (select_ok) {
+					struct sock *sk2;
+
+					sk2 = reuseport_select_sock(sk, hash, skb,
+							sizeof(struct udphdr));
+					if (sk2) {
+						result = sk2;
+						select_ok = false;
+						goto found;
+					}
 				}
 				matches = 1;
 			}
@@ -321,6 +326,7 @@ struct sock *__udp6_lib_lookup(struct net *net,
 	unsigned int hash2, slot2, slot = udp_hashfn(net, hnum, udptable->mask);
 	struct udp_hslot *hslot2, *hslot = &udptable->hash[slot];
 	int score, badness, matches = 0, reuseport = 0;
+	bool select_ok = true;
 	u32 hash = 0;
 
 	rcu_read_lock();
@@ -358,14 +364,18 @@ struct sock *__udp6_lib_lookup(struct net *net,
 			badness = score;
 			reuseport = sk->sk_reuseport;
 			if (reuseport) {
-				struct sock *sk2;
 				hash = udp6_ehashfn(net, daddr, hnum,
 						    saddr, sport);
-				sk2 = reuseport_select_sock(sk, hash, skb,
+				if (select_ok) {
+					struct sock *sk2;
+
+					sk2 = reuseport_select_sock(sk, hash, skb,
 							sizeof(struct udphdr));
-				if (sk2) {
-					result = sk2;
-					goto found;
+					if (sk2) {
+						result = sk2;
+						select_ok = false;
+						goto found;
+					}
 				}
 				matches = 1;
 			}
