kernel: backport upstream fix for CVE-2018-5390

Backport an upstream fix for a remotely exploitable TCP denial of service
flaw in Linux 4.9+.

The fixes are included in Linux 4.14.59 and later but did not yet end up in
version 4.9.118.

Signed-off-by: Jo-Philipp Wich <jo@mein.io>

target/linux/generic/backport-4.9/100-tcp-add-tcp_ooo_try_coalesce-helper.patch

@@ -0,0 +1,76 @@
+From 74b120c45aebf4278e1dedc55f5fa24d8ea83cdc Mon Sep 17 00:00:00 2001
+From: Eric Dumazet <edumazet@google.com>
+Date: Mon, 23 Jul 2018 09:28:21 -0700
+Subject: tcp: add tcp_ooo_try_coalesce() helper
+
+commit 58152ecbbcc6a0ce7fddd5bf5f6ee535834ece0c upstream.
+
+In case skb in out_or_order_queue is the result of
+multiple skbs coalescing, we would like to get a proper gso_segs
+counter tracking, so that future tcp_drop() can report an accurate
+number.
+
+I chose to not implement this tracking for skbs in receive queue,
+since they are not dropped, unless socket is disconnected.
+
+Signed-off-by: Eric Dumazet <edumazet@google.com>
+Acked-by: Soheil Hassas Yeganeh <soheil@google.com>
+Acked-by: Yuchung Cheng <ycheng@google.com>
+Signed-off-by: David S. Miller <davem@davemloft.net>
+Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
+Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
+---
+ net/ipv4/tcp_input.c | 23 +++++++++++++++++++++--
+ 1 file changed, 21 insertions(+), 2 deletions(-)
+
+diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
+index a9be8df108b4..9d0b73aa649f 100644
+--- a/net/ipv4/tcp_input.c
++++ b/net/ipv4/tcp_input.c
+@@ -4370,6 +4370,23 @@ static bool tcp_try_coalesce(struct sock *sk,
+ 	return true;
+ }
+ 
++static bool tcp_ooo_try_coalesce(struct sock *sk,
++			     struct sk_buff *to,
++			     struct sk_buff *from,
++			     bool *fragstolen)
++{
++	bool res = tcp_try_coalesce(sk, to, from, fragstolen);
++
++	/* In case tcp_drop() is called later, update to->gso_segs */
++	if (res) {
++		u32 gso_segs = max_t(u16, 1, skb_shinfo(to)->gso_segs) +
++			       max_t(u16, 1, skb_shinfo(from)->gso_segs);
++
++		skb_shinfo(to)->gso_segs = min_t(u32, gso_segs, 0xFFFF);
++	}
++	return res;
++}
++
+ static void tcp_drop(struct sock *sk, struct sk_buff *skb)
+ {
+ 	sk_drops_add(sk, skb);
+@@ -4493,7 +4510,8 @@ static void tcp_data_queue_ofo(struct sock *sk, struct sk_buff *skb)
+ 	/* In the typical case, we are adding an skb to the end of the list.
+ 	 * Use of ooo_last_skb avoids the O(Log(N)) rbtree lookup.
+ 	 */
+-	if (tcp_try_coalesce(sk, tp->ooo_last_skb, skb, &fragstolen)) {
++	if (tcp_ooo_try_coalesce(sk, tp->ooo_last_skb,
++				 skb, &fragstolen)) {
+ coalesce_done:
+ 		tcp_grow_window(sk, skb);
+ 		kfree_skb_partial(skb, fragstolen);
+@@ -4543,7 +4561,8 @@ coalesce_done:
+ 				tcp_drop(sk, skb1);
+ 				goto merge_right;
+ 			}
+-		} else if (tcp_try_coalesce(sk, skb1, skb, &fragstolen)) {
++		} else if (tcp_ooo_try_coalesce(sk, skb1,
++						skb, &fragstolen)) {
+ 			goto coalesce_done;
+ 		}
+ 		p = &parent->rb_right;
+-- 
+cgit 1.2-0.3.lf.el7
+