tcp: Fix tcp_make_synack()

Commit 4957faad (TCPCT part 1g: Responder Cookie => Initiator), part
of TCP_COOKIE_TRANSACTION implementation, forgot to correctly size
synack skb in case user data must be included.

Many thanks to Mika Pentillä for spotting this error.

Reported-by: Penttillä Mika <mika.penttila@ixonos.com>
Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 9 insertions, 9 deletions

diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index 4a1605d3f909..f181b78f2385 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -2395,13 +2395,17 @@ struct sk_buff *tcp_make_synack(struct sock *sk, struct dst_entry *dst,
         struct tcp_extend_values *xvp = tcp_xv(rvp);
         struct inet_request_sock *ireq = inet_rsk(req);
         struct tcp_sock *tp = tcp_sk(sk);
+        const struct tcp_cookie_values *cvp = tp->cookie_values;
         struct tcphdr *th;
         struct sk_buff *skb;
         struct tcp_md5sig_key *md5;
         int tcp_header_size;
         int mss;
+        int s_data_desired = 0;
 
-        skb = sock_wmalloc(sk, MAX_TCP_HEADER + 15, 1, GFP_ATOMIC);
+        if (cvp != NULL && cvp->s_data_constant && cvp->s_data_desired)
+                s_data_desired = cvp->s_data_desired;
+        skb = sock_wmalloc(sk, MAX_TCP_HEADER + 15 + s_data_desired, 1, GFP_ATOMIC);
         if (skb == NULL)
                 return NULL;
 
@@ -2457,16 +2461,12 @@ struct sk_buff *tcp_make_synack(struct sock *sk, struct dst_entry *dst,
                              TCPCB_FLAG_SYN | TCPCB_FLAG_ACK);
 
         if (OPTION_COOKIE_EXTENSION & opts.options) {
-                const struct tcp_cookie_values *cvp = tp->cookie_values;
-
-                if (cvp != NULL &&
-                    cvp->s_data_constant &&
-                    cvp->s_data_desired > 0) {
-                        u8 *buf = skb_put(skb, cvp->s_data_desired);
+                if (s_data_desired) {
+                        u8 *buf = skb_put(skb, s_data_desired);
 
                         /* copy data directly from the listening socket. */
-                        memcpy(buf, cvp->s_data_payload, cvp->s_data_desired);
-                        TCP_SKB_CB(skb)->end_seq += cvp->s_data_desired;
+                        memcpy(buf, cvp->s_data_payload, s_data_desired);
+                        TCP_SKB_CB(skb)->end_seq += s_data_desired;
                 }
 
                 if (opts.hash_size > 0) {