net-tcp: fastopen: fix high order allocations

This patch fixes two bugs in fastopen :

1) The tcp_sendmsg(...,  @size) argument was ignored.

   Code was relying on user not fooling the kernel with iovec mismatches

2) When MTU is about 64KB, tcp_send_syn_data() attempts order-5
allocations, which are likely to fail when memory gets fragmented.

Fixes: 783237e8daf13 ("net-tcp: Fast Open client - sending SYN-data")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Yuchung Cheng <ycheng@google.com>
Acked-by: Yuchung Cheng <ycheng@google.com>
Tested-by: Yuchung Cheng <ycheng@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

3 files changed, 13 insertions, 5 deletions

diff --git a/include/net/tcp.h b/include/net/tcp.h
index 56fc366da6d5..8c4dd63134d4 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -1303,7 +1303,8 @@ struct tcp_fastopen_request {
         /* Fast Open cookie. Size 0 means a cookie request */
         struct tcp_fastopen_cookie      cookie;
         struct msghdr                   *data;  /* data in MSG_FASTOPEN */
-        u16                             copied; /* queued in tcp_connect() */
+        size_t                          size;
+        int                             copied; /* queued in tcp_connect() */
 };
 void tcp_free_fastopen_req(struct tcp_sock *tp);
 
diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index 9f3a2db9109e..97c8f5620c43 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -1044,7 +1044,8 @@ void tcp_free_fastopen_req(struct tcp_sock *tp)
         }
 }
 
-static int tcp_sendmsg_fastopen(struct sock *sk, struct msghdr *msg, int *size)
+static int tcp_sendmsg_fastopen(struct sock *sk, struct msghdr *msg,
+                                int *copied, size_t size)
 {
         struct tcp_sock *tp = tcp_sk(sk);
         int err, flags;
@@ -1059,11 +1060,12 @@ static int tcp_sendmsg_fastopen(struct sock *sk, struct msghdr *msg, int *size)
         if (unlikely(tp->fastopen_req == NULL))
                 return -ENOBUFS;
         tp->fastopen_req->data = msg;
+        tp->fastopen_req->size = size;
 
         flags = (msg->msg_flags & MSG_DONTWAIT) ? O_NONBLOCK : 0;
         err = __inet_stream_connect(sk->sk_socket, msg->msg_name,
                                     msg->msg_namelen, flags);
-        *size = tp->fastopen_req->copied;
+        *copied = tp->fastopen_req->copied;
         tcp_free_fastopen_req(tp);
         return err;
 }
@@ -1083,7 +1085,7 @@ int tcp_sendmsg(struct kiocb *iocb, struct sock *sk, struct msghdr *msg,
 
         flags = msg->msg_flags;
         if (flags & MSG_FASTOPEN) {
-                err = tcp_sendmsg_fastopen(sk, msg, &copied_syn);
+                err = tcp_sendmsg_fastopen(sk, msg, &copied_syn, size);
                 if (err == -EINPROGRESS && copied_syn > 0)
                         goto out;
                 else if (err)
diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index 3be16727f058..09805817627b 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -2908,7 +2908,12 @@ static int tcp_send_syn_data(struct sock *sk, struct sk_buff *syn)
         space = __tcp_mtu_to_mss(sk, inet_csk(sk)->icsk_pmtu_cookie) -
                 MAX_TCP_OPTION_SPACE;
 
-        syn_data = skb_copy_expand(syn, skb_headroom(syn), space,
+        space = min_t(size_t, space, fo->size);
+
+        /* limit to order-0 allocations */
+        space = min_t(size_t, space, SKB_MAX_HEAD(MAX_TCP_HEADER));
+
+        syn_data = skb_copy_expand(syn, MAX_TCP_HEADER, space,
                                    sk->sk_allocation);
         if (syn_data == NULL)
                 goto fallback;