inet: add RCU protection to inet->opt

We lack proper synchronization to manipulate inet->opt ip_options

Problem is ip_make_skb() calls ip_setup_cork() and
ip_setup_cork() possibly makes a copy of ipc->opt (struct ip_options),
without any protection against another thread manipulating inet->opt.

Another thread can change inet->opt pointer and free old one under us.

Use RCU to protect inet->opt (changed to inet->inet_opt).

Instead of handling atomic refcounts, just copy ip_options when
necessary, to avoid cache line dirtying.

We cant insert an rcu_head in struct ip_options since its included in
skb->cb[], so this patch is large because I had to introduce a new
ip_options_rcu structure.

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Cc: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 3 insertions, 3 deletions

diff --git a/net/ipv4/inet_connection_sock.c b/net/ipv4/inet_connection_sock.c
index 8514db54a7f4..3282cb2de393 100644
--- a/net/ipv4/inet_connection_sock.c
+++ b/net/ipv4/inet_connection_sock.c
@@ -354,20 +354,20 @@ struct dst_entry *inet_csk_route_req(struct sock *sk,
 {
         struct rtable *rt;
         const struct inet_request_sock *ireq = inet_rsk(req);
-        struct ip_options *opt = inet_rsk(req)->opt;
+        struct ip_options_rcu *opt = inet_rsk(req)->opt;
         struct net *net = sock_net(sk);
         struct flowi4 fl4;
 
         flowi4_init_output(&fl4, sk->sk_bound_dev_if, sk->sk_mark,
                            RT_CONN_FLAGS(sk), RT_SCOPE_UNIVERSE,
                            sk->sk_protocol, inet_sk_flowi_flags(sk),
-                           (opt && opt->srr) ? opt->faddr : ireq->rmt_addr,
+                           (opt && opt->opt.srr) ? opt->opt.faddr : ireq->rmt_addr,
                            ireq->loc_addr, ireq->rmt_port, inet_sk(sk)->inet_sport);
         security_req_classify_flow(req, flowi4_to_flowi(&fl4));
         rt = ip_route_output_flow(net, &fl4, sk);
         if (IS_ERR(rt))
                 goto no_route;
-        if (opt && opt->is_strictroute && rt->rt_dst != rt->rt_gateway)
+        if (opt && opt->opt.is_strictroute && rt->rt_dst != rt->rt_gateway)
                 goto route_err;
         return &rt->dst;