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-rw-r--r--net/ipv4/tcp_input.c73
1 files changed, 73 insertions, 0 deletions
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 8892df6de1d4..706cbb3b2986 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -3782,6 +3782,49 @@ static void smc_parse_options(const struct tcphdr *th,
#endif
}
+/* Try to parse the MSS option from the TCP header. Return 0 on failure, clamped
+ * value on success.
+ */
+static u16 tcp_parse_mss_option(const struct tcphdr *th, u16 user_mss)
+{
+ const unsigned char *ptr = (const unsigned char *)(th + 1);
+ int length = (th->doff * 4) - sizeof(struct tcphdr);
+ u16 mss = 0;
+
+ while (length > 0) {
+ int opcode = *ptr++;
+ int opsize;
+
+ switch (opcode) {
+ case TCPOPT_EOL:
+ return mss;
+ case TCPOPT_NOP: /* Ref: RFC 793 section 3.1 */
+ length--;
+ continue;
+ default:
+ if (length < 2)
+ return mss;
+ opsize = *ptr++;
+ if (opsize < 2) /* "silly options" */
+ return mss;
+ if (opsize > length)
+ return mss; /* fail on partial options */
+ if (opcode == TCPOPT_MSS && opsize == TCPOLEN_MSS) {
+ u16 in_mss = get_unaligned_be16(ptr);
+
+ if (in_mss) {
+ if (user_mss && user_mss < in_mss)
+ in_mss = user_mss;
+ mss = in_mss;
+ }
+ }
+ ptr += opsize - 2;
+ length -= opsize;
+ }
+ }
+ return mss;
+}
+
/* Look for tcp options. Normally only called on SYN and SYNACK packets.
* But, this can also be called on packets in the established flow when
* the fast version below fails.
@@ -6464,6 +6507,36 @@ static void tcp_reqsk_record_syn(const struct sock *sk,
}
}
+/* If a SYN cookie is required and supported, returns a clamped MSS value to be
+ * used for SYN cookie generation.
+ */
+u16 tcp_get_syncookie_mss(struct request_sock_ops *rsk_ops,
+ const struct tcp_request_sock_ops *af_ops,
+ struct sock *sk, struct tcphdr *th)
+{
+ struct tcp_sock *tp = tcp_sk(sk);
+ u16 mss;
+
+ if (sock_net(sk)->ipv4.sysctl_tcp_syncookies != 2 &&
+ !inet_csk_reqsk_queue_is_full(sk))
+ return 0;
+
+ if (!tcp_syn_flood_action(sk, rsk_ops->slab_name))
+ return 0;
+
+ if (sk_acceptq_is_full(sk)) {
+ NET_INC_STATS(sock_net(sk), LINUX_MIB_LISTENOVERFLOWS);
+ return 0;
+ }
+
+ mss = tcp_parse_mss_option(th, tp->rx_opt.user_mss);
+ if (!mss)
+ mss = af_ops->mss_clamp;
+
+ return mss;
+}
+EXPORT_SYMBOL_GPL(tcp_get_syncookie_mss);
+
int tcp_conn_request(struct request_sock_ops *rsk_ops,
const struct tcp_request_sock_ops *af_ops,
struct sock *sk, struct sk_buff *skb)