syncookies: check decoded options against sysctl settings

Discard the ACK if we find options that do not match current sysctl
settings.

Previously it was possible to create a connection with sack, wscale,
etc. enabled even if the feature was disabled via sysctl.

Also remove an unneeded call to tcp_sack_reset() in
cookie_check_timestamp: Both call sites (cookie_v4_check,
cookie_v6_check) zero "struct tcp_options_received", hand it to
tcp_parse_options() (which does not change tcp_opt->num_sacks/dsack)
and then call cookie_check_timestamp().

Even if num_sacks/dsacks were changed, the structure is allocated on
the stack and after cookie_check_timestamp returns only a few selected
members are copied to the inet_request_sock.

Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 2 insertions, 2 deletions

diff --git a/net/ipv6/syncookies.c b/net/ipv6/syncookies.c
index 70d330f8c990..c7ee57421ece 100644
--- a/net/ipv6/syncookies.c
+++ b/net/ipv6/syncookies.c
@@ -180,8 +180,8 @@ struct sock *cookie_v6_check(struct sock *sk, struct sk_buff *skb)
         memset(&tcp_opt, 0, sizeof(tcp_opt));
         tcp_parse_options(skb, &tcp_opt, &hash_location, 0);
 
-        if (tcp_opt.saw_tstamp)
-                cookie_check_timestamp(&tcp_opt);
+        if (!cookie_check_timestamp(&tcp_opt))
+                goto out;
 
         ret = NULL;
         req = inet6_reqsk_alloc(&tcp6_request_sock_ops);