ipv6: add complete rcu protection around np->opt

This patch addresses multiple problems :

UDP/RAW sendmsg() need to get a stable struct ipv6_txoptions
while socket is not locked : Other threads can change np->opt
concurrently. Dmitry posted a syzkaller
(http://github.com/google/syzkaller) program desmonstrating
use-after-free.

Starting with TCP/DCCP lockless listeners, tcp_v6_syn_recv_sock()
and dccp_v6_request_recv_sock() also need to use RCU protection
to dereference np->opt once (before calling ipv6_dup_options())

This patch adds full RCU protection to np->opt

Reported-by: Dmitry Vyukov <dvyukov@google.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Acked-by: Hannes Frederic Sowa <hannes@stressinduktion.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 8 insertions, 3 deletions

diff --git a/net/ipv6/inet6_connection_sock.c b/net/ipv6/inet6_connection_sock.c
index 5d1c7cee2cb2..3ff5208772bb 100644
--- a/net/ipv6/inet6_connection_sock.c
+++ b/net/ipv6/inet6_connection_sock.c
@@ -78,7 +78,9 @@ struct dst_entry *inet6_csk_route_req(const struct sock *sk,
         memset(fl6, 0, sizeof(*fl6));
         fl6->flowi6_proto = proto;
         fl6->daddr = ireq->ir_v6_rmt_addr;
-        final_p = fl6_update_dst(fl6, np->opt, &final);
+        rcu_read_lock();
+        final_p = fl6_update_dst(fl6, rcu_dereference(np->opt), &final);
+        rcu_read_unlock();
         fl6->saddr = ireq->ir_v6_loc_addr;
         fl6->flowi6_oif = ireq->ir_iif;
         fl6->flowi6_mark = ireq->ir_mark;
@@ -142,7 +144,9 @@ static struct dst_entry *inet6_csk_route_socket(struct sock *sk,
         fl6->fl6_dport = inet->inet_dport;
         security_sk_classify_flow(sk, flowi6_to_flowi(fl6));
 
-        final_p = fl6_update_dst(fl6, np->opt, &final);
+        rcu_read_lock();
+        final_p = fl6_update_dst(fl6, rcu_dereference(np->opt), &final);
+        rcu_read_unlock();
 
         dst = __inet6_csk_dst_check(sk, np->dst_cookie);
         if (!dst) {
@@ -175,7 +179,8 @@ int inet6_csk_xmit(struct sock *sk, struct sk_buff *skb, struct flowi *fl_unused
         /* Restore final destination back after routing done */
         fl6.daddr = sk->sk_v6_daddr;
 
-        res = ip6_xmit(sk, skb, &fl6, np->opt, np->tclass);
+        res = ip6_xmit(sk, skb, &fl6, rcu_dereference(np->opt),
+                       np->tclass);
         rcu_read_unlock();
         return res;
 }