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, 2 insertions, 2 deletions

diff --git a/net/ipv4/syncookies.c b/net/ipv4/syncookies.c
index 71e029691908..26461492a847 100644
--- a/net/ipv4/syncookies.c
+++ b/net/ipv4/syncookies.c
@@ -321,10 +321,10 @@ struct sock *cookie_v4_check(struct sock *sk, struct sk_buff *skb,
          * the ACK carries the same options again (see RFC1122 4.2.3.8)
          */
         if (opt && opt->optlen) {
-                int opt_size = sizeof(struct ip_options) + opt->optlen;
+                int opt_size = sizeof(struct ip_options_rcu) + opt->optlen;
 
                 ireq->opt = kmalloc(opt_size, GFP_ATOMIC);
-                if (ireq->opt != NULL && ip_options_echo(ireq->opt, skb)) {
+                if (ireq->opt != NULL && ip_options_echo(&ireq->opt->opt, skb)) {
                         kfree(ireq->opt);
                         ireq->opt = NULL;
                 }