[PATCH 3.16 253/410] udplite: fix partial checksum initialization

[Ben Hutchings]

3.16.57-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Alexey Kodanev <alexey.kodanev@xxxxxxxxxx>

commit 15f35d49c93f4fa9875235e7bf3e3783d2dd7a1b upstream.

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@xxxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
 include/net/udplite.h   | 1 +
 net/ipv4/udp.c          | 5 +++++
 net/ipv6/ip6_checksum.c | 5 +++++
 3 files changed, 11 insertions(+)

--- a/include/net/udplite.h
+++ b/include/net/udplite.h
@@ -61,6 +61,7 @@ static inline int udplite_checksum_init(
 		UDP_SKB_CB(skb)->cscov = cscov;
 		if (skb->ip_summed == CHECKSUM_COMPLETE)
 			skb->ip_summed = CHECKSUM_NONE;
+		skb->csum_valid = 0;
         }
 
 	return 0;
--- a/net/ipv4/udp.c
+++ b/net/ipv4/udp.c
@@ -1729,6 +1729,11 @@ static inline int udp4_csum_init(struct
 		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;
+		}
 	}
 
 	return skb_checksum_init_zero_check(skb, proto, uh->check,
--- a/net/ipv6/ip6_checksum.c
+++ b/net/ipv6/ip6_checksum.c
@@ -73,6 +73,11 @@ int udp6_csum_init(struct sk_buff *skb,
 		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)