udp6: fix socket leak on early demux

Paolo Abeni · davem330 · commit c9f2c1ae123a · 2017-07-29T14:19:03.000-07:00
When an early demuxed packet reaches __udp6_lib_lookup_skb(), the sk reference is retrieved and used, but the relevant reference count is leaked and the socket destructor is never called. Beyond leaking the sk memory, if there are pending UDP packets in the receive queue, even the related accounted memory is leaked. In the long run, this will cause persistent forward allocation errors and no UDP skbs (both ipv4 and ipv6) will be able to reach the user-space. Fix this by explicitly accessing the early demux reference before the lookup, and properly decreasing the socket reference count after usage. Also drop the skb_steal_sock() in __udp6_lib_lookup_skb(), and the now obsoleted comment about "socket cache". The newly added code is derived from the current ipv4 code for the similar path. v1 -> v2: fixed the __udp6_lib_rcv() return code for resubmission, as suggested by Eric Reported-by: Sam Edwards <CFSworks@gmail.com> Reported-by: Marc Haber <mh+netdev@zugschlus.de> Fixes: 5425077 ("net: ipv6: Add early demux handler for UDP unicast") Signed-off-by: Paolo Abeni <pabeni@redhat.com> Acked-by: Eric Dumazet <edumazet@google.com> Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/include/net/udp.h b/include/net/udp.h
@@ -260,6 +260,7 @@ static inline struct sk_buff *skb_recv_udp(struct sock *sk, unsigned int flags,
 }
 
 void udp_v4_early_demux(struct sk_buff *skb);
+void udp_sk_rx_dst_set(struct sock *sk, struct dst_entry *dst);
 int udp_get_port(struct sock *sk, unsigned short snum,
 		 int (*saddr_cmp)(const struct sock *,
 				  const struct sock *));
diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c
@@ -1928,7 +1928,7 @@ static int udp_queue_rcv_skb(struct sock *sk, struct sk_buff *skb)
 /* For TCP sockets, sk_rx_dst is protected by socket lock
  * For UDP, we use xchg() to guard against concurrent changes.
  */
-static void udp_sk_rx_dst_set(struct sock *sk, struct dst_entry *dst)
+void udp_sk_rx_dst_set(struct sock *sk, struct dst_entry *dst)
 {
 	struct dst_entry *old;
 
@@ -1937,6 +1937,7 @@ static void udp_sk_rx_dst_set(struct sock *sk, struct dst_entry *dst)
 		dst_release(old);
 	}
 }
+EXPORT_SYMBOL(udp_sk_rx_dst_set);
 
 /*
  *	Multicasts and broadcasts go to each listener.
diff --git a/net/ipv6/udp.c b/net/ipv6/udp.c
@@ -291,11 +291,7 @@ static struct sock *__udp6_lib_lookup_skb(struct sk_buff *skb,
 					  struct udp_table *udptable)
 {
 	const struct ipv6hdr *iph = ipv6_hdr(skb);
-	struct sock *sk;
 
-	sk = skb_steal_sock(skb);
-	if (unlikely(sk))
-		return sk;
 	return __udp6_lib_lookup(dev_net(skb->dev), &iph->saddr, sport,
 				 &iph->daddr, dport, inet6_iif(skb),
 				 udptable, skb);
@@ -804,6 +800,24 @@ int __udp6_lib_rcv(struct sk_buff *skb, struct udp_table *udptable,
 	if (udp6_csum_init(skb, uh, proto))
 		goto csum_error;
 
+	/* Check if the socket is already available, e.g. due to early demux */
+	sk = skb_steal_sock(skb);
+	if (sk) {
+		struct dst_entry *dst = skb_dst(skb);
+		int ret;
+
+		if (unlikely(sk->sk_rx_dst != dst))
+			udp_sk_rx_dst_set(sk, dst);
+
+		ret = udpv6_queue_rcv_skb(sk, skb);
+		sock_put(sk);
+
+		/* a return value > 0 means to resubmit the input */
+		if (ret > 0)
+			return ret;
+		return 0;
+	}
+
 	/*
 	 *	Multicast receive code
 	 */
@@ -812,11 +826,6 @@ int __udp6_lib_rcv(struct sk_buff *skb, struct udp_table *udptable,
 				saddr, daddr, udptable, proto);
 
 	/* Unicast */
-
-	/*
-	 * check socket cache ... must talk to Alan about his plans
-	 * for sock caches... i'll skip this for now.
-	 */
 	sk = __udp6_lib_lookup_skb(skb, uh->source, uh->dest, udptable);
 	if (sk) {
 		int ret;

Original file line number	Diff line number	Diff line change
`@@ -260,6 +260,7 @@ static inline struct sk_buff skb_recv_udp(struct sock sk, unsigned int flags,`
`260`	`260`	`}`
`261`	`261`
`262`	`262`	`void udp_v4_early_demux(struct sk_buff *skb);`
	`263`	`+void udp_sk_rx_dst_set(struct sock sk, struct dst_entry dst);`
`263`	`264`	`int udp_get_port(struct sock *sk, unsigned short snum,`
`264`	`265`	`int (saddr_cmp)(const struct sock ,`
`265`	`266`	`const struct sock *));`
Original file line number	Diff line number	Diff line change
`@@ -1928,7 +1928,7 @@ static int udp_queue_rcv_skb(struct sock sk, struct sk_buff skb)`
`1928`	`1928`	`/* For TCP sockets, sk_rx_dst is protected by socket lock`
`1929`	`1929`	`* For UDP, we use xchg() to guard against concurrent changes.`
`1930`	`1930`	`*/`
`1931`		`-static void udp_sk_rx_dst_set(struct sock sk, struct dst_entry dst)`
	`1931`	`+void udp_sk_rx_dst_set(struct sock sk, struct dst_entry dst)`
`1932`	`1932`	`{`
`1933`	`1933`	`struct dst_entry *old;`
`1934`	`1934`
`@@ -1937,6 +1937,7 @@ static void udp_sk_rx_dst_set(struct sock sk, struct dst_entry dst)`
`1937`	`1937`	`dst_release(old);`
`1938`	`1938`	`}`
`1939`	`1939`	`}`
	`1940`	`+EXPORT_SYMBOL(udp_sk_rx_dst_set);`
`1940`	`1941`
`1941`	`1942`	`/*`
`1942`	`1943`	`* Multicasts and broadcasts go to each listener.`