net: ipv6: Fix UDP early demux lookup with udp_l3mdev_accept=0"

David Ahern reported that "net: ipv6: Add early demux
handler for UDP unicast" breaks udp_l3mdev_accept=0 since early
demux for IPv6 UDP was doing a generic socket lookup which does not
require an exact match. Fix this by making UDPv6 early demux match
connected sockets only.

v1->v2: Take reference to socket after match as suggested by Eric
v2->v3: Add comment before break

CRs-Fixed: 2057820
Change-Id: Ief9fd4a51561b7a49efa3780ebe8dc3632bdfa1c
Fixes: 5425077d73e0c ("net: ipv6: Add early demux handler for UDP unicast")
Reported-by: David Ahern <dsa@cumulusnetworks.com>
Signed-off-by: Subash Abhinov Kasiviswanathan <subashab@codeaurora.org>
Cc: Eric Dumazet <edumazet@google.com>
Acked-by: David Ahern <dsa@cumulusnetworks.com>
Tested-by: David Ahern <dsa@cumulusnetworks.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Git-commit: 0bd84065b19bca12f07f288c8ea470e2c1b2de7a
Git-repo: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
[subashab@codeaurora.org: resolve trivial merge conflicts]

1 files changed, 17 insertions, 10 deletions

diff --git a/net/ipv6/udp.c b/net/ipv6/udp.c
index 8a07c63ddccd..a48a8faa401c 100644
--- a/net/ipv6/udp.c
+++ b/net/ipv6/udp.c
@@ -45,6 +45,7 @@
 #include <net/tcp_states.h>
 #include <net/ip6_checksum.h>
 #include <net/xfrm.h>
+#include <net/inet_hashtables.h>
 #include <net/inet6_hashtables.h>
 #include <net/busy_poll.h>
 
@@ -964,15 +965,21 @@ static struct sock *__udp6_lib_demux_lookup(struct net *net,
 			int dif)
 {
 	struct sock *sk;
-
-	rcu_read_lock();
-	sk = __udp6_lib_lookup(net, rmt_addr, rmt_port, loc_addr, loc_port,
-			       dif, &udp_table);
-	if (sk && !atomic_inc_not_zero(&sk->sk_refcnt))
-		sk = NULL;
-	rcu_read_unlock();
-
-	return sk;
+	struct hlist_nulls_node *hnode;
+	unsigned short hnum = ntohs(loc_port);
+	unsigned int hash2 = udp6_portaddr_hash(net, loc_addr, hnum);
+	unsigned int slot2 = hash2 & udp_table.mask;
+	struct udp_hslot *hslot2 = &udp_table.hash2[slot2];
+
+	const __portpair ports = INET_COMBINED_PORTS(rmt_port, hnum);
+
+	udp_portaddr_for_each_entry_rcu(sk, hnode, &hslot2->head) {
+		if (INET6_MATCH(sk, net, rmt_addr, loc_addr, ports, dif))
+			return sk;
+		/* Only check first socket in chain */
+		break;
+	}
+	return NULL;
 }
 
 static void udp_v6_early_demux(struct sk_buff *skb)
@@ -997,7 +1004,7 @@ static void udp_v6_early_demux(struct sk_buff *skb)
 	else
 		return;
 
-	if (!sk)
+	if (!sk || !atomic_inc_not_zero_hint(&sk->sk_refcnt, 2))
 		return;
 
 	skb->sk = sk;