tcp: fix FIONREAD/SIOCINQ

tcp_ioctl() tries to take into account if tcp socket received a FIN
to report correct number bytes in receive queue.

But its flaky because if the application ate the last skb,
we return 1 instead of 0.

Correct way to detect that FIN was received is to test SOCK_DONE.

Reported-by: Elliot Hughes <enh@google.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Neal Cardwell <ncardwell@google.com>
Cc: Tom Herbert <therbert@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 3 insertions, 5 deletions

diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index f32c02e2a543..b7c2f439b54f 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -549,14 +549,12 @@ int tcp_ioctl(struct sock *sk, int cmd, unsigned long arg)
                          !tp->urg_data ||
                          before(tp->urg_seq, tp->copied_seq) ||
                          !before(tp->urg_seq, tp->rcv_nxt)) {
-                        struct sk_buff *skb;
 
                         answ = tp->rcv_nxt - tp->copied_seq;
 
-                        /* Subtract 1, if FIN is in queue. */
-                        skb = skb_peek_tail(&sk->sk_receive_queue);
-                        if (answ && skb)
-                                answ -= tcp_hdr(skb)->fin;
+                        /* Subtract 1, if FIN was received */
+                        if (answ && sock_flag(sk, SOCK_DONE))
+                                answ--;
                 } else
                         answ = tp->urg_seq - tp->copied_seq;
                 release_sock(sk);