[PATCH 4.4 26/36] udplite: fix partial checksum initialization

Greg Kroah-Hartman
2018-03-10T00:20:38Z

From: Alexey Kodanev <alexey.kodanev@oracle.com>

[ Upstream commit 15f35d49c93f4fa9875235e7bf3e3783d2dd7a1b ]

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
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
@@ -62,6 +62,7 @@ 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
@@ -1744,6 +1744,11 @@ 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)