[PATCH] tcp: fix FIONREAD/SIOCINQ

[Eric Dumazet <eric.dumazet@gmail.com>]

From: Eric Dumazet <edumazet@google.com>

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>
---
 net/ipv4/tcp.c |    8 +++-----
 1 file changed, 3 insertions(+), 5 deletions(-)

diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index f32c02e..b7c2f43 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);