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>
diff --git a/net/ipv4/syncookies.c b/net/ipv4/syncookies.c
index 02bef6a..51b5662 100644
--- a/net/ipv4/syncookies.c
+++ b/net/ipv4/syncookies.c
@@ -230,23 +230,36 @@
* The lowest 4 bits are for snd_wscale
* The next 4 lsb are for rcv_wscale
* The next lsb is for sack_ok
+ *
+ * return false if we decode an option that should not be.
*/
-void cookie_check_timestamp(struct tcp_options_received *tcp_opt)
+bool cookie_check_timestamp(struct tcp_options_received *tcp_opt)
{
/* echoed timestamp, 9 lowest bits contain options */
u32 options = tcp_opt->rcv_tsecr & TSMASK;
+ if (!tcp_opt->saw_tstamp) {
+ tcp_clear_options(tcp_opt);
+ return true;
+ }
+
+ if (!sysctl_tcp_timestamps)
+ return false;
+
tcp_opt->snd_wscale = options & 0xf;
options >>= 4;
tcp_opt->rcv_wscale = options & 0xf;
tcp_opt->sack_ok = (options >> 4) & 0x1;
- if (tcp_opt->sack_ok)
- tcp_sack_reset(tcp_opt);
+ if (tcp_opt->sack_ok && !sysctl_tcp_sack)
+ return false;
- if (tcp_opt->snd_wscale || tcp_opt->rcv_wscale)
+ if (tcp_opt->snd_wscale || tcp_opt->rcv_wscale) {
tcp_opt->wscale_ok = 1;
+ return sysctl_tcp_window_scaling != 0;
+ }
+ return true;
}
EXPORT_SYMBOL(cookie_check_timestamp);
@@ -281,8 +294,8 @@
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 = inet_reqsk_alloc(&tcp_request_sock_ops); /* for safety */