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, 12 insertions, 5 deletions

diff --git a/net/ipv4/af_inet.c b/net/ipv4/af_inet.c
index 0413af3e2285..963a621e75c7 100644
--- a/net/ipv4/af_inet.c
+++ b/net/ipv4/af_inet.c
@@ -153,7 +153,7 @@ void inet_sock_destruct(struct sock *sk)
         WARN_ON(sk->sk_wmem_queued);
         WARN_ON(sk->sk_forward_alloc);
 
-        kfree(inet->opt);
+        kfree(rcu_dereference_protected(inet->inet_opt, 1));
         dst_release(rcu_dereference_check(sk->sk_dst_cache, 1));
         sk_refcnt_debug_dec(sk);
 }
@@ -1106,9 +1106,12 @@ static int inet_sk_reselect_saddr(struct sock *sk)
         struct flowi4 fl4;
         struct rtable *rt;
         __be32 new_saddr;
+        struct ip_options_rcu *inet_opt;
 
-        if (inet->opt && inet->opt->srr)
-                daddr = inet->opt->faddr;
+        inet_opt = rcu_dereference_protected(inet->inet_opt,
+                                             sock_owned_by_user(sk));
+        if (inet_opt && inet_opt->opt.srr)
+                daddr = inet_opt->opt.faddr;
 
         /* Query new route. */
         rt = ip_route_connect(&fl4, daddr, 0, RT_CONN_FLAGS(sk),
@@ -1148,6 +1151,7 @@ int inet_sk_rebuild_header(struct sock *sk)
         struct inet_sock *inet = inet_sk(sk);
         struct rtable *rt = (struct rtable *)__sk_dst_check(sk, 0);
         __be32 daddr;
+        struct ip_options_rcu *inet_opt;
         int err;
 
         /* Route is OK, nothing to do. */
@@ -1155,9 +1159,12 @@ int inet_sk_rebuild_header(struct sock *sk)
                 return 0;
 
         /* Reroute. */
+        rcu_read_lock();
+        inet_opt = rcu_dereference(inet->inet_opt);
         daddr = inet->inet_daddr;
-        if (inet->opt && inet->opt->srr)
-                daddr = inet->opt->faddr;
+        if (inet_opt && inet_opt->opt.srr)
+                daddr = inet_opt->opt.faddr;
+        rcu_read_unlock();
         rt = ip_route_output_ports(sock_net(sk), sk, daddr, inet->inet_saddr,
                                    inet->inet_dport, inet->inet_sport,
                                    sk->sk_protocol, RT_CONN_FLAGS(sk),