tcp: fix race in tcp_v6_syn_recv_sock()

[ Upstream commit d37fe4255abe8e7b419b90c5847e8ec2b8debb08 ]

tcp_v6_syn_recv_sock() calls ip6_dst_store() before
inet_sk(newsk)->pinet6 has been set up.

This means ip6_dst_store() writes over the parent (listener)
np->dst_cookie.

This is racy because multiple threads could share the same
parent and their final np->dst_cookie could be wrong.

Move ip6_dst_store() call after inet_sk(newsk)->pinet6
has been changed and after the copy of parent ipv6_pinfo.

Fixes: e994b2f0fb92 ("tcp: do not lock listener to process SYN packets")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/net/ipv6/tcp_ipv6.c b/net/ipv6/tcp_ipv6.c
index 7cb622d300aa23fc169014d8964809c56d34640b..c5efbfe2a2c4aab8fd6d23c4569190c8754be7ba 100644 (file)
--- a/net/ipv6/tcp_ipv6.c
+++ b/net/ipv6/tcp_ipv6.c
@@ -1228,7 +1228,6 @@ static struct sock *tcp_v6_syn_recv_sock(const struct sock *sk, struct sk_buff *
         */
 
        newsk->sk_gso_type = SKB_GSO_TCPV6;
-       ip6_dst_store(newsk, dst, NULL, NULL);
        inet6_sk_rx_dst_set(newsk, skb);
 
        inet_sk(newsk)->pinet6 = tcp_inet6_sk(newsk);
@@ -1239,6 +1238,8 @@ static struct sock *tcp_v6_syn_recv_sock(const struct sock *sk, struct sk_buff *
 
        memcpy(newnp, np, sizeof(struct ipv6_pinfo));
 
+       ip6_dst_store(newsk, dst, NULL, NULL);
+
        newsk->sk_v6_daddr = ireq->ir_v6_rmt_addr;
        newnp->saddr = ireq->ir_v6_loc_addr;
        newsk->sk_v6_rcv_saddr = ireq->ir_v6_loc_addr;