tcp: RFC7413 option support for Fast Open server

Fast Open has been using the experimental option with a magic number
(RFC6994) to request and grant Fast Open cookies. This patch enables
the server to support the official IANA option 34 in RFC7413 in
addition.

The change has passed all existing Fast Open tests with both
old and new options at Google.

Signed-off-by: Daniel Lee <Longinus00@gmail.com>
Signed-off-by: Yuchung Cheng <ycheng@google.com>
Signed-off-by: Neal Cardwell <ncardwell@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

3 files changed, 54 insertions, 23 deletions

diff --git a/net/ipv4/tcp_fastopen.c b/net/ipv4/tcp_fastopen.c
index 5da55e2b5cd2..e3d87aca6be8 100644
--- a/net/ipv4/tcp_fastopen.c
+++ b/net/ipv4/tcp_fastopen.c
@@ -303,6 +303,7 @@ fastopen:
 	} else if (foc->len > 0) /* Client presents an invalid cookie */
 		NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPFASTOPENPASSIVEFAIL);
 
+	valid_foc.exp = foc->exp;
 	*foc = valid_foc;
 	return false;
 }
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index c1ce304ba8d2..24f1630b2afb 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -3603,6 +3603,23 @@ old_ack:
 	return 0;
 }
 
+static void tcp_parse_fastopen_option(int len, const unsigned char *cookie,
+				      bool syn, struct tcp_fastopen_cookie *foc,
+				      bool exp_opt)
+{
+	/* Valid only in SYN or SYN-ACK with an even length.  */
+	if (!foc || !syn || len < 0 || (len & 1))
+		return;
+
+	if (len >= TCP_FASTOPEN_COOKIE_MIN &&
+	    len <= TCP_FASTOPEN_COOKIE_MAX)
+		memcpy(foc->val, cookie, len);
+	else if (len != 0)
+		len = -1;
+	foc->len = len;
+	foc->exp = exp_opt;
+}
+
 /* 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.
@@ -3692,21 +3709,22 @@ void tcp_parse_options(const struct sk_buff *skb,
 				 */
 				break;
 #endif
+			case TCPOPT_FASTOPEN:
+				tcp_parse_fastopen_option(
+					opsize - TCPOLEN_FASTOPEN_BASE,
+					ptr, th->syn, foc, false);
+				break;
+
 			case TCPOPT_EXP:
 				/* Fast Open option shares code 254 using a
-				 * 16 bits magic number. It's valid only in
-				 * SYN or SYN-ACK with an even size.
+				 * 16 bits magic number.
 				 */
-				if (opsize < TCPOLEN_EXP_FASTOPEN_BASE ||
-				    get_unaligned_be16(ptr) != TCPOPT_FASTOPEN_MAGIC ||
-				    !foc || !th->syn || (opsize & 1))
-					break;
-				foc->len = opsize - TCPOLEN_EXP_FASTOPEN_BASE;
-				if (foc->len >= TCP_FASTOPEN_COOKIE_MIN &&
-				    foc->len <= TCP_FASTOPEN_COOKIE_MAX)
-					memcpy(foc->val, ptr + 2, foc->len);
-				else if (foc->len != 0)
-					foc->len = -1;
+				if (opsize >= TCPOLEN_EXP_FASTOPEN_BASE &&
+				    get_unaligned_be16(ptr) ==
+				    TCPOPT_FASTOPEN_MAGIC)
+					tcp_parse_fastopen_option(opsize -
+						TCPOLEN_EXP_FASTOPEN_BASE,
+						ptr + 2, th->syn, foc, true);
 				break;
 
 			}
diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index 7404e5238e00..464bd8c5de69 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -518,17 +518,26 @@ static void tcp_options_write(__be32 *ptr, struct tcp_sock *tp,
 
 	if (unlikely(OPTION_FAST_OPEN_COOKIE & options)) {
 		struct tcp_fastopen_cookie *foc = opts->fastopen_cookie;
+		u8 *p = (u8 *)ptr;
+		u32 len; /* Fast Open option length */
+
+		if (foc->exp) {
+			len = TCPOLEN_EXP_FASTOPEN_BASE + foc->len;
+			*ptr = htonl((TCPOPT_EXP << 24) | (len << 16) |
+				     TCPOPT_FASTOPEN_MAGIC);
+			p += TCPOLEN_EXP_FASTOPEN_BASE;
+		} else {
+			len = TCPOLEN_FASTOPEN_BASE + foc->len;
+			*p++ = TCPOPT_FASTOPEN;
+			*p++ = len;
+		}
 
-		*ptr++ = htonl((TCPOPT_EXP << 24) |
-			       ((TCPOLEN_EXP_FASTOPEN_BASE + foc->len) << 16) |
-			       TCPOPT_FASTOPEN_MAGIC);
-
-		memcpy(ptr, foc->val, foc->len);
-		if ((foc->len & 3) == 2) {
-			u8 *align = ((u8 *)ptr) + foc->len;
-			align[0] = align[1] = TCPOPT_NOP;
+		memcpy(p, foc->val, foc->len);
+		if ((len & 3) == 2) {
+			p[foc->len] = TCPOPT_NOP;
+			p[foc->len + 1] = TCPOPT_NOP;
 		}
-		ptr += (foc->len + 3) >> 2;
+		ptr += (len + 3) >> 2;
 	}
 }
 
@@ -641,8 +650,11 @@ static unsigned int tcp_synack_options(struct sock *sk,
 		if (unlikely(!ireq->tstamp_ok))
 			remaining -= TCPOLEN_SACKPERM_ALIGNED;
 	}
-	if (foc && foc->len >= 0) {
-		u32 need = TCPOLEN_EXP_FASTOPEN_BASE + foc->len;
+	if (foc != NULL && foc->len >= 0) {
+		u32 need = foc->len;
+
+		need += foc->exp ? TCPOLEN_EXP_FASTOPEN_BASE :
+				   TCPOLEN_FASTOPEN_BASE;
 		need = (need + 3) & ~3U;  /* Align to 32 bits */
 		if (remaining >= need) {
 			opts->options |= OPTION_FAST_OPEN_COOKIE;