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>

1 files changed, 23 insertions, 11 deletions

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;