ipv6: do not clear pinet6 field

We have seen multiple NULL dereferences in __inet6_lookup_established()

After analysis, I found that inet6_sk() could be NULL while the
check for sk_family == AF_INET6 was true.

Bug was added in linux-2.6.29 when RCU lookups were introduced in UDP
and TCP stacks.

Once an IPv6 socket, using SLAB_DESTROY_BY_RCU is inserted in a hash
table, we no longer can clear pinet6 field.

This patch extends logic used in commit fcbdf09d9652c891
("net: fix nulls list corruptions in sk_prot_alloc")

TCP/UDP/UDPLite IPv6 protocols provide their own .clear_sk() method
to make sure we do not clear pinet6 field.

At socket clone phase, we do not really care, as cloning the parent (non
NULL) pinet6 is not adding a fatal race.

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

1 files changed, 12 insertions, 1 deletions

diff --git a/net/ipv6/udp.c b/net/ipv6/udp.c
index d4defdd..42923b1 100644
--- a/net/ipv6/udp.c
+++ b/net/ipv6/udp.c
@@ -1432,6 +1432,17 @@ void udp6_proc_exit(struct net *net) {
 }
 #endif /* CONFIG_PROC_FS */
 
+void udp_v6_clear_sk(struct sock *sk, int size)
+{
+	struct inet_sock *inet = inet_sk(sk);
+
+	/* we do not want to clear pinet6 field, because of RCU lookups */
+	sk_prot_clear_portaddr_nulls(sk, offsetof(struct inet_sock, pinet6));
+
+	size -= offsetof(struct inet_sock, pinet6) + sizeof(inet->pinet6);
+	memset(&inet->pinet6 + 1, 0, size);
+}
+
 /* ------------------------------------------------------------------------ */
 
 struct proto udpv6_prot = {
@@ -1462,7 +1473,7 @@ struct proto udpv6_prot = {
 	.compat_setsockopt = compat_udpv6_setsockopt,
 	.compat_getsockopt = compat_udpv6_getsockopt,
 #endif
-	.clear_sk	   = sk_prot_clear_portaddr_nulls,
+	.clear_sk	   = udp_v6_clear_sk,
 };
 
 static struct inet_protosw udpv6_protosw = {