Re: [PATCH] netfilter: fix IPv6 NTP checksum calculation

[Ulrich Weber <ulrich.weber@gmail.com>]

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Hi Jean-Michel,

can you please test again with Yoshifuji's patches and attached patch?
I think csum16_add() is still not proper, we would also need a carry bit if
"result < a". We better use the internal checksum functions if possible...

Cheers
  Ulrich

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>From 40e0c6d86514a8dcc80f18fbe8a2945c6ee78f6d Mon Sep 17 00:00:00 2001
From: Ulrich Weber <ulrich.weber@sophos.com>
Date: Tue, 29 Jan 2013 15:24:21 +0100
Subject: [PATCH] netfilter: ip6t_NTP: Use onces complement of csum_fold

we need a 16bit value but not folded

Signed-off-by: Ulrich Weber <ulrich.weber@sophos.com>
---
 net/ipv6/netfilter/ip6t_NPT.c |    6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/net/ipv6/netfilter/ip6t_NPT.c b/net/ipv6/netfilter/ip6t_NPT.c
index 74e171d..61a9b95 100644
--- a/net/ipv6/netfilter/ip6t_NPT.c
+++ b/net/ipv6/netfilter/ip6t_NPT.c
@@ -35,7 +35,7 @@ static int ip6t_npt_checkentry(const struct xt_tgchk_param *par)
 	src_sum = csum_partial(&npt->src_pfx.in6, sizeof(npt->src_pfx.in6), 0);
 	dst_sum = csum_partial(&npt->dst_pfx.in6, sizeof(npt->dst_pfx.in6), 0);
 
-	npt->adjustment = csum_fold(csum_sub(src_sum, dst_sum));
+	npt->adjustment = ~csum_fold(csum_sub(src_sum, dst_sum));
 	return 0;
 }
 
@@ -71,8 +71,8 @@ static bool ip6t_npt_map_pfx(const struct ip6t_npt_tginfo *npt,
 			return false;
 	}
 
-	sum = csum_fold(csum_add(csum_unfold((__force __sum16)addr->s6_addr16[idx]),
-				 csum_unfold(npt->adjustment)));
+	sum = ~csum_fold(csum_add(csum_unfold((__force __sum16)addr->s6_addr16[idx]),
+				  csum_unfold(npt->adjustment)));
 	if (sum == CSUM_MANGLED_0)
 		sum = 0;
 	*(__force __sum16 *)&addr->s6_addr16[idx] = sum;
-- 
1.7.9.5