From: Alexey Kodanev <alexey.kodanev@oracle.com>
Date: Thu, 15 Feb 2018 20:18:43 +0300
Subject: udplite: fix partial checksum initialization
Patch-mainline: v4.16-rc3
Git-commit: 15f35d49c93f4fa9875235e7bf3e3783d2dd7a1b
References: bsc#1076830

Since UDP-Lite is always using checksum, the following path is
triggered when calculating pseudo header for it:

  udp4_csum_init() or udp6_csum_init()
    skb_checksum_init_zero_check()
      __skb_checksum_validate_complete()

The problem can appear if skb->len is less than CHECKSUM_BREAK. In
this particular case __skb_checksum_validate_complete() also invokes
__skb_checksum_complete(skb). If UDP-Lite is using partial checksum
that covers only part of a packet, the function will return bad
checksum and the packet will be dropped.

It can be fixed if we skip skb_checksum_init_zero_check() and only
set the required pseudo header checksum for UDP-Lite with partial
checksum before udp4_csum_init()/udp6_csum_init() functions return.

Fixes: ed70fcfcee95 ("net: Call skb_checksum_init in IPv4")
Fixes: e4f45b7f40bd ("net: Call skb_checksum_init in IPv6")
Signed-off-by: Alexey Kodanev <alexey.kodanev@oracle.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Acked-by: Michal Kubecek <mkubecek@suse.cz>

---
 include/net/udplite.h   | 1 +
 net/ipv4/udp.c          | 5 +++++
 net/ipv6/ip6_checksum.c | 5 +++++
 3 files changed, 11 insertions(+)

diff --git a/include/net/udplite.h b/include/net/udplite.h
index b7a18f63d86d..acc064e21917 100644
--- a/include/net/udplite.h
+++ b/include/net/udplite.h
@@ -63,6 +63,7 @@ static inline int udplite_checksum_init(struct sk_buff *skb, struct udphdr *uh)
 		UDP_SKB_CB(skb)->cscov = cscov;
 		if (skb->ip_summed == CHECKSUM_COMPLETE)
 			skb->ip_summed = CHECKSUM_NONE;
+		skb->csum_valid = 0;
         }
 
 	return 0;
diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c
index a86c0d84f7a1..eb4d62765ec7 100644
--- a/net/ipv4/udp.c
+++ b/net/ipv4/udp.c
@@ -1972,6 +1972,11 @@ static inline int udp4_csum_init(struct sk_buff *skb, struct udphdr *uh,
 		err = udplite_checksum_init(skb, uh);
 		if (err)
 			return err;
+
+		if (UDP_SKB_CB(skb)->partial_cov) {
+			skb->csum = inet_compute_pseudo(skb, proto);
+			return 0;
+		}
 	}
 
 	/* Note, we are only interested in != 0 or == 0, thus the
diff --git a/net/ipv6/ip6_checksum.c b/net/ipv6/ip6_checksum.c
index c0cbcb259f5a..1dc023ca98fd 100644
--- a/net/ipv6/ip6_checksum.c
+++ b/net/ipv6/ip6_checksum.c
@@ -72,6 +72,11 @@ int udp6_csum_init(struct sk_buff *skb, struct udphdr *uh, int proto)
 		err = udplite_checksum_init(skb, uh);
 		if (err)
 			return err;
+
+		if (UDP_SKB_CB(skb)->partial_cov) {
+			skb->csum = ip6_compute_pseudo(skb, proto);
+			return 0;
+		}
 	}
 
 	/* To support RFC 6936 (allow zero checksum in UDP/IPV6 for tunnels)
-- 
2.16.2