From aea0929e516a1ff4c4458203d1f3375eee9acc26 Mon Sep 17 00:00:00 2001
From: Eric B Munson <emunson@akamai.com>
Date: Mon, 18 May 2015 14:35:58 -0400
Subject: tcp: Return error instead of partial read for saved syn headers

Currently the getsockopt() requesting the cached contents of the syn
packet headers will fail silently if the caller uses a buffer that is
too small to contain the requested data.  Rather than fail silently and
discard the headers, getsockopt() should return an error and report the
required size to hold the data.

Signed-off-by: Eric B Munson <emunson@akamai.com>
Cc: Eric Dumazet <edumazet@google.com>
Cc: Alexey Kuznetsov <kuznet@ms2.inr.ac.ru>
Cc: James Morris <jmorris@namei.org>
Cc: Hideaki YOSHIFUJI <yoshfuji@linux-ipv6.org>
Cc: Patrick McHardy <kaber@trash.net>
Cc: netdev@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index c724195..bb9bb84 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -2845,7 +2845,15 @@ static int do_tcp_getsockopt(struct sock *sk, int level,
 
 		lock_sock(sk);
 		if (tp->saved_syn) {
-			len = min_t(unsigned int, tp->saved_syn[0], len);
+			if (len < tp->saved_syn[0]) {
+				if (put_user(tp->saved_syn[0], optlen)) {
+					release_sock(sk);
+					return -EFAULT;
+				}
+				release_sock(sk);
+				return -EINVAL;
+			}
+			len = tp->saved_syn[0];
 			if (put_user(len, optlen)) {
 				release_sock(sk);
 				return -EFAULT;
-- 
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