netfilter: nf_nat_snmp: fix checksum calculation (v4)

Fix checksum calculation in nf_nat_snmp_basic.

Based on patches by Clark Wang <wtweeker@163.com> and
Stephen Hemminger <shemminger@vyatta.com>.

https://bugzilla.kernel.org/show_bug.cgi?id=17622

Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 4 insertions, 2 deletions

diff --git a/net/ipv4/netfilter/nf_nat_snmp_basic.c b/net/ipv4/netfilter/nf_nat_snmp_basic.c
index 1679e2c0963d..ee5f419d0a56 100644
--- a/net/ipv4/netfilter/nf_nat_snmp_basic.c
+++ b/net/ipv4/netfilter/nf_nat_snmp_basic.c
@@ -893,13 +893,15 @@ static void fast_csum(__sum16 *csum,
         unsigned char s[4];
 
         if (offset & 1) {
-                s[0] = s[2] = 0;
+                s[0] = ~0;
                 s[1] = ~*optr;
+                s[2] = 0;
                 s[3] = *nptr;
         } else {
-                s[1] = s[3] = 0;
                 s[0] = ~*optr;
+                s[1] = ~0;
                 s[2] = *nptr;
+                s[3] = 0;
         }
 
         *csum = csum_fold(csum_partial(s, 4, ~csum_unfold(*csum)));