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

[Jean-Michel DILLY <jm@dilly.me>]

Hi,

Here is the signed-off patch.

Signed-off-by: Jean-Michel DILLY <jm@dilly.me>
---
diff --git a/ip6t_NPT.c b/linux-3.8-rc4/net/ipv6/netfilter/ip6t_NPT.c
index 787748b..29ef720 100644
--- a/ip6t_NPT.c
+++ b/linux-3.8-rc4/net/ipv6/netfilter/ip6t_NPT.c
@@ -14,24 +14,44 @@
#include <linux/netfilter_ipv6/ip6t_NPT.h>
#include <linux/netfilter/x_tables.h>

+static __sum16 csum16_add(__sum16 a, __sum16 b)
+{
+       __u16 result;
+
+       result = (__force __u16) a + (__force __u16) b;
+       result += result < (__force __u16)b; 
+               
+
+       return (__force __sum16) result;
+}
+
+static __sum16 csum16_complement(__sum16 a)
+{
+       return (__force __sum16)(0xffff - (__force u16)a);
+}
+
+static __sum16 csum16_sub(__sum16 a, __sum16 b)
+{
+       return csum16_add(a, csum16_complement(b));
+}

static int ip6t_npt_checkentry(const struct xt_tgchk_param *par)
{
       struct ip6t_npt_tginfo *npt = par->targinfo;
-       __wsum src_sum = 0, dst_sum = 0;
+       __sum16 src_sum = 0, dst_sum = 0;
       unsigned int i;

       if (npt->src_pfx_len > 64 || npt->dst_pfx_len > 64)
               return -EINVAL;

       for (i = 0; i < ARRAY_SIZE(npt->src_pfx.in6.s6_addr16); i++) {
-               src_sum = csum_add(src_sum,
-                       (__force __wsum)npt->src_pfx.in6.s6_addr16[i]);
-               dst_sum = csum_add(dst_sum,
-                       (__force __wsum)npt->dst_pfx.in6.s6_addr16[i]);
+               src_sum = csum16_add(src_sum, 
+                                       (__force __sum16)npt->src_pfx.in6.s6_addr16[i]);
+               dst_sum = csum16_add(dst_sum, 
+                                       (__force __sum16)npt->dst_pfx.in6.s6_addr16[i]);
       }

-       npt->adjustment = (__force __sum16) csum_sub(src_sum, dst_sum);
+       npt->adjustment = csum16_sub(src_sum, dst_sum);
       return 0;
}

@@ -67,8 +87,8 @@ static bool ip6t_npt_map_pfx(const struct ip6t_npt_tginfo *npt,
                       return false;
       }

-       sum = (__force __sum16) csum_add((__force __wsum)addr->s6_addr16[idx],
-                        npt->adjustment);
+       sum = csum16_add((__force __sum16)addr->s6_addr16[idx],
+                               npt->adjustment);
       if (sum == CSUM_MANGLED_0)
               sum = 0;
       *(__force __sum16 *)&addr->s6_addr16[idx] = sum;

Le 24 janv. 2013 à 23:49, Florian Westphal a écrit :

> Jean-Michel DILLY <jm@dilly.me> wrote:
>> Hi all,
>> This patch doesn't work as expected. I tried with few IP and each time 0x0100 were missing. csum_add seems buggy too.
>> I have reimplemented csum16s functions with the Ulrich's fix. It seems to work now.
>> I'm a noob, so I guess someone will propose a better patch for this.
> 
> We can't use csum_add after all, patch looks correct.
> 
> Can you re-send with proper Signoff?
> 
> [ carry detection breaks on overflow, e.g. a==1 and b=0xffff yields
>  0 for csum_add (65536 < 1) and 1 for csum16_add (0 < 1) ]
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