[PATCH] netfilter: fix IPv6 NTP checksum calculation

[PATCH] netfilter: fix IPv6 NTP checksum calculation

[Ulrich Weber]

csum16_add() has a broken carry detection, should be:
sum += sum < (__force u16)b;

Instead of fixing csum16_add, remove the custom checksum
functions and use the generic csum_add/csum_sub ones.

Signed-off-by: Ulrich Weber <ulrich.weber@sophos.com>
---
 net/ipv6/netfilter/ip6t_NPT.c |   33 +++++++--------------------------
 1 file changed, 7 insertions(+), 26 deletions(-)

diff --git a/net/ipv6/netfilter/ip6t_NPT.c b/net/ipv6/netfilter/ip6t_NPT.c
index e948691..7302b0b 100644
--- a/net/ipv6/netfilter/ip6t_NPT.c
+++ b/net/ipv6/netfilter/ip6t_NPT.c
@@ -14,42 +14,23 @@
 #include <linux/netfilter_ipv6/ip6t_NPT.h>
 #include <linux/netfilter/x_tables.h>
 
-static __sum16 csum16_complement(__sum16 a)
-{
-	return (__force __sum16)(0xffff - (__force u16)a);
-}
-
-static __sum16 csum16_add(__sum16 a, __sum16 b)
-{
-	u16 sum;
-
-	sum = (__force u16)a + (__force u16)b;
-	sum += (__force u16)a < (__force u16)b;
-	return (__force __sum16)sum;
-}
-
-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;
-	__sum16 src_sum = 0, dst_sum = 0;
+	__wsum 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 = 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]);
+		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]);
 	}
 
-	npt->adjustment = csum16_sub(src_sum, dst_sum);
+	npt->adjustment = (__force __sum16) csum_sub(src_sum, dst_sum);
 	return 0;
 }
 
@@ -85,7 +66,7 @@ static bool ip6t_npt_map_pfx(const struct ip6t_npt_tginfo *npt,
 			return false;
 	}
 
-	sum = csum16_add((__force __sum16)addr->s6_addr16[idx],
+	sum = (__force __sum16) csum_add((__force __wsum)addr->s6_addr16[idx],
 			 npt->adjustment);
 	if (sum == CSUM_MANGLED_0)
 		sum = 0;
-- 
1.7.9.5

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

[Patrick McHardy]

On Wed, Jan 02, 2013 at 04:24:40PM +0100, Ulrich Weber wrote:
> csum16_add() has a broken carry detection, should be:
> sum += sum < (__force u16)b;
> 
> Instead of fixing csum16_add, remove the custom checksum
> functions and use the generic csum_add/csum_sub ones.

Looks good to me.

Acked-by: Patrick McHardy <kaber@trash.net>

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

[Pablo Neira Ayuso]

On Fri, Jan 04, 2013 at 10:20:43AM +0100, Patrick McHardy wrote:
> On Wed, Jan 02, 2013 at 04:24:40PM +0100, Ulrich Weber wrote:
> > csum16_add() has a broken carry detection, should be:
> > sum += sum < (__force u16)b;
> > 
> > Instead of fixing csum16_add, remove the custom checksum
> > functions and use the generic csum_add/csum_sub ones.
> 
> Looks good to me.
> 
> Acked-by: Patrick McHardy <kaber@trash.net>

Applied, thanks!

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

[Jean-Michel DILLY]

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.
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;

Regards,
JMichel

On Fri, Jan 04, 2013 at 10:20:43AM +0100, Patrick McHardy wrote:
> > On Wed, Jan 02, 2013 at 04:24:40PM +0100, Ulrich Weber wrote:
> > > csum16_add() has a broken carry detection, should be:
> > > sum += sum < (__force u16)b;
> > > 
> > > Instead of fixing csum16_add, remove the custom checksum
> > > functions and use the generic csum_add/csum_sub ones.
> > 
> > Looks good to me.
> > 
> > Acked-by: Patrick McHardy <kaber@trash.net>

>Applied, thanks!

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

[Florian Westphal]

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) ]

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

[Jean-Michel DILLY]

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

[YOSHIFUJI Hideaki]

Jean-Michel DILLY wrote:
> 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) ]

Well... why do you fill npt->adjustment?
I think we can do checksumming in ip6t_npt_map_pfx()
with csum_partial(), csum_block_add()/csum_block_sub() and
csum_fold().

--yoshfuji


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

[Ulrich Weber]

[-- Attachment #1: Type: text/plain, Size: 256 bytes --]

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

[-- Attachment #2: 0001-netfilter-ip6t_NTP-Use-onces-complement-of-csum_fold.patch --]
[-- Type: text/x-patch, Size: 1412 bytes --]

>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