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New: SAMEIP --nodst functionality gone missing

Bugme-new Andrew Morton 4 participants 9 messages Apr 7, 2009 – Apr 17, 2009 1 message not in the archive

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A message that is not in the archive (sent off-list or not yet received): [email protected]/

Andrew Morton

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#1 lore raw

(switched to email. Please respond via emailed reply-to-all, not via the bugzilla web interface).

"massive issues"!

Quoted 46 lines · On Fri, 27 Mar 2009 16:48:06 GMT [email protected] wrote:

http://bugzilla.kernel.org/show_bug.cgi?id=12954

           Summary: SAMEIP --nodst functionality gone missing
           Product: Networking
           Version: 2.5
    Kernel Version: 2.6.25+
          Platform: All
        OS/Version: Linux
              Tree: Mainline
            Status: NEW
          Severity: normal
          Priority: P1
         Component: Netfilter/Iptables
        AssignedTo: [email protected]
        ReportedBy: [email protected]
        Regression: Yes

This was already briefly discussed on the netfilter mailinglist, but did not spark much response there. However I think this issue is a pretty obvious regression over old kernel versions and might hit quite a few people once the newer kernels get deployed into large NAT setups.

Back in the days of 2.6.18 there was the SAME target which allowed, with the option '--nodst' to SNAT internal hosts to the same address of a whole SNAT range regardless of the destination address.

In cb76c6a597350534d211ba79d92da1f9771f8226 the SAME target was removed from the kernel sources due to being obsolete, since the same functionality was now in nf_nat. Shortly after that a discussion Patrick McHardy proposed a patch to mimic the behaviour of SAME with --nodst in nf_nat by dropping the destination IP from the jhash. The patch was dropped shortly after because it apparently showed some uneven distribution.

The whole thread can be read at
http://thread.gmane.org/gmane.comp.security.firewalls.netfilter.devel/23275/focus=27670
.

This thread went dead, I tried to revive it but did not get an answer. We're getting hit by this regression because we are currently NATing some thousand IP addresses (student dorms) to an external /28. It works fine with our old 2.6.18+SAME setup, but tests with 2.6.25+SNAT showed massive issues with connections from the same internal address to different destinations getting NATed to different addresses in the pool. Which breaks, for example, ICQ quite badly.

#2 lore raw
Quoted 15 lines · Andrew Morton
Quoted 15 lines

Back in the days of 2.6.18 there was the SAME target which allowed, with the option '--nodst' to SNAT internal hosts to the same address of a whole SNAT range regardless of the destination address.

In cb76c6a597350534d211ba79d92da1f9771f8226 the SAME target was removed from the kernel sources due to being obsolete, since the same functionality was now in nf_nat. Shortly after that a discussion Patrick McHardy proposed a patch to mimic the behaviour of SAME with --nodst in nf_nat by dropping the destination IP from the jhash. The patch was dropped shortly after because it apparently showed some uneven distribution.

The whole thread can be read at
http://thread.gmane.org/gmane.comp.security.firewalls.netfilter.devel/23275/focus=27670
.

Quoted 7 lines
Quoted 7 lines

This thread went dead, I tried to revive it but did not get an answer. We're getting hit by this regression because we are currently NATing some thousand IP addresses (student dorms) to an external /28. It works fine with our old 2.6.18+SAME setup, but tests with 2.6.25+SNAT showed massive issues with connections from the same internal address to different destinations getting NATed to different addresses in the pool. Which breaks, for example, ICQ quite badly.

Problems like these were the reason why I wrote the SAME target in the first place. I NAT'ed a few hundred students behind a small range of ipaddresses and with normal SNAT they had extreme problems with ICQ and online banking sites which require you to have the same source ip even if you move between servers (diffrent destinations) etc.

After I wrote SAME I didn't get a single complaint.

One bonus feature that many students really liked was that they always had the same external ipaddress as long as they had the same internal ipaddress and the external range of ipaddresses remained the same.

This feature isn't as important as having the same source ip for all current sessions when using online banking services etc.

I didn't think anyone was still using SAME... guess I was wrong.

The uneven distribution of the patch in question can't be worse than the SAME distributions which, iirc, just does something like:

first_ip_in_snat_range + (client_ip % num_ips_in_snat_range)

And given many clients behind the SNAT the distribution should be quite even.

Patrick, how about making the ipaddress selection based on only client ipaddress behaviour selectable with an SNAT parameter if the problem with the patch is that the distribution can be uneven for a small number of clients?

/Martin

#3 lore raw

[Resend to mailing list, I didn't notice this had left bugzilla]

Quoted 1 line · Martin Josefsson

Patrick, how about making the ipaddress selection based on only client ipaddress behaviour selectable with an SNAT parameter if the problem with the patch is that the distribution can be uneven for a small number of clients?

Actually I think the results back then were incorrect or it was just bad luck or something. Ideally we would just enable this unconditionally I think. I'll do some testing of the distribution myself during the next days and see how it goes.

#4 lore raw
Quoted 9 lines · Patrick McHardy

[Resend to mailing list, I didn't notice this had left bugzilla]

Quoted 1 line · Martin Josefsson

Patrick, how about making the ipaddress selection based on only client ipaddress behaviour selectable with an SNAT parameter if the problem with the patch is that the distribution can be uneven for a small number of clients?

Actually I think the results back then were incorrect or it was just bad luck or something. Ideally we would just enable this unconditionally I think. I'll do some testing of the distribution myself during the next days and see how it goes.

The distribution did suffer noticably in some cases, so offering this optionally seems better.

How about this patch? If the IP_NAT_RANGE_PERSISTENT flag is set on a NAT range, we ignore the destination address in the selection.

include/net/netfilter/nf_nat.h +1 -0
index 9dc1039..8df0b7f 100644
@@ -18,6 +18,7 @@ enum nf_nat_manip_type
 #define IP_NAT_RANGE_MAP_IPS 1
 #define IP_NAT_RANGE_PROTO_SPECIFIED 2
 #define IP_NAT_RANGE_PROTO_RANDOM 4
+#define IP_NAT_RANGE_PERSISTENT 8
 
 /* NAT sequence number modifications */
 struct nf_nat_seq {
net/ipv4/netfilter/nf_nat_core.c +2 -1
index fe65187..3229e0a 100644
@@ -211,7 +211,8 @@ find_best_ips_proto(struct nf_conntrack_tuple *tuple,
 	minip = ntohl(range->min_ip);
 	maxip = ntohl(range->max_ip);
 	j = jhash_2words((__force u32)tuple->src.u3.ip,
-			 (__force u32)tuple->dst.u3.ip, 0);
+			 range->flags & IP_NAT_RANGE_PERSISTENT ?
+				(__force u32)tuple->dst.u3.ip : 0, 0);
 	j = ((u64)j * (maxip - minip + 1)) >> 32;
 	*var_ipp = htonl(minip + j);
 }
#5 lore raw
Quoted 13 lines · Patrick McHardy
Quoted 11 lines · Patrick McHardy

[Resend to mailing list, I didn't notice this had left bugzilla]

Quoted 3 lines · Martin Josefsson

Patrick, how about making the ipaddress selection based on only client ipaddress behaviour selectable with an SNAT parameter if the problem with the patch is that the distribution can be uneven for a small number of clients?

Actually I think the results back then were incorrect or it was just bad luck or something. Ideally we would just enable this unconditionally I think. I'll do some testing of the distribution myself during the next days and see how it goes.

Quoted 5 lines

The distribution did suffer noticably in some cases, so offering this optionally seems better.

How about this patch? If the IP_NAT_RANGE_PERSISTENT flag is set on a NAT range, we ignore the destination address in the selection.

But where do you set IP_NAT_RANGE_PERSISTENT? (It seems like a dead feature right now.)

#6 lore raw
Quoted 9 lines · Jan Engelhardt
Quoted 3 lines · Patrick McHardy

How about this patch? If the IP_NAT_RANGE_PERSISTENT flag is set on a NAT range, we ignore the destination address in the selection.

But where do you set IP_NAT_RANGE_PERSISTENT? (It seems like a dead feature right now.)

In userspace of course :)

#7 lore raw
Quoted 10 lines · Patrick McHardy
Quoted 7 lines · Jan Engelhardt
Quoted 2 lines · Patrick McHardy

How about this patch? If the IP_NAT_RANGE_PERSISTENT flag is set on a NAT range, we ignore the destination address in the selection.

But where do you set IP_NAT_RANGE_PERSISTENT? (It seems like a dead feature right now.)

In userspace of course :)

Ah I hear the crisp sound of an upcoming iptables 1.4.4.

#8 lore raw
Quoted 10 lines · Jan Engelhardt
Quoted 7 lines · Patrick McHardy
Quoted 5 lines · Jan Engelhardt
Quoted 2 lines · Patrick McHardy

How about this patch? If the IP_NAT_RANGE_PERSISTENT flag is set on a NAT range, we ignore the destination address in the selection.

But where do you set IP_NAT_RANGE_PERSISTENT? (It seems like a dead feature right now.)

In userspace of course :)

Ah I hear the crisp sound of an upcoming iptables 1.4.4.

In a while :)

This is the corresponding userspace patch:

extensions/libipt_DNAT.c +11 -1
index b5f8028..dc79b44 100644
@@ -27,12 +27,13 @@ static void DNAT_help(void)
 "DNAT target options:\n"
 " --to-destination <ipaddr>[-<ipaddr>][:port-port]\n"
 "				Address to map destination to.\n"
-"[--random]\n");
+"[--random] [--persistent]\n");
 }
 
 static const struct option DNAT_opts[] = {
 	{ "to-destination", 1, NULL, '1' },
 	{ "random", 0, NULL, '2' },
+	{ "persistent", 0, NULL, '3' },
 	{ .name = NULL }
 };
 

@@ -178,6 +179,11 @@ static int DNAT_parse(int c, char **argv, int invert, unsigned int *flags,
 		} else
 			*flags |= IPT_DNAT_OPT_RANDOM;
 		return 1;
+
+	case '3':
+		info->mr.range[0].flags |= IP_NAT_RANGE_PERSISTENT;
+		return 1;
+
 	default:
 		return 0;
 	}

@@ -222,6 +228,8 @@ static void DNAT_print(const void *ip, const struct xt_entry_target *target,
 		printf(" ");
 		if (info->mr.range[i].flags & IP_NAT_RANGE_PROTO_RANDOM)
 			printf("random ");
+		if (info->mr.range[i].flags & IP_NAT_RANGE_PERSISTENT)
+			printf("persistent ");
 	}
 }
 

@@ -236,6 +244,8 @@ static void DNAT_save(const void *ip, const struct xt_entry_target *target)
 		printf(" ");
 		if (info->mr.range[i].flags & IP_NAT_RANGE_PROTO_RANDOM)
 			printf("--random ");
+		if (info->mr.range[i].flags & IP_NAT_RANGE_PERSISTENT)
+			printf("--persistent ");
 	}
 }
extensions/libipt_SNAT.c +10 -1
index 944fe67..762d8d0 100644
@@ -27,12 +27,13 @@ static void SNAT_help(void)
 "SNAT target options:\n"
 " --to-source <ipaddr>[-<ipaddr>][:port-port]\n"
 "				Address to map source to.\n"
-"[--random]\n");
+"[--random] [ --persistent]\n");
 }
 
 static const struct option SNAT_opts[] = {
 	{ "to-source", 1, NULL, '1' },
 	{ "random", 0, NULL, '2' },
+	{ "perstistent", 0, NULL, '3' },
 	{ .name = NULL }
 };
 

@@ -179,6 +180,10 @@ static int SNAT_parse(int c, char **argv, int invert, unsigned int *flags,
 			*flags |= IPT_SNAT_OPT_RANDOM;
 		return 1;
 
+	case '3':
+		info->mr.range[0].flags |= IP_NAT_RANGE_PERSISTENT;
+		return 1;
+
 	default:
 		return 0;
 	}

@@ -223,6 +228,8 @@ static void SNAT_print(const void *ip, const struct xt_entry_target *target,
 		printf(" ");
 		if (info->mr.range[i].flags & IP_NAT_RANGE_PROTO_RANDOM)
 			printf("random ");
+		if (info->mr.range[i].flags & IP_NAT_RANGE_PERSISTENT)
+			printf("persistent ");
 	}
 }
 

@@ -237,6 +244,8 @@ static void SNAT_save(const void *ip, const struct xt_entry_target *target)
 		printf(" ");
 		if (info->mr.range[i].flags & IP_NAT_RANGE_PROTO_RANDOM)
 			printf("--random ");
+		if (info->mr.range[i].flags & IP_NAT_RANGE_PERSISTENT)
+			printf("--persistent ");
 	}
 }
include/net/netfilter/nf_nat.h +1 -0
index 094473e..c3e2060 100644
@@ -18,6 +18,7 @@ enum nf_nat_manip_type
 #define IP_NAT_RANGE_MAP_IPS 1
 #define IP_NAT_RANGE_PROTO_SPECIFIED 2
 #define IP_NAT_RANGE_PROTO_RANDOM 4
+#define IP_NAT_RANGE_PERSISTENT 8
 
 /* NAT sequence number modifications */
 struct nf_nat_seq {
#9 lore raw
Quoted 2 lines · Patrick McHardy

This is the corresponding userspace patch:

I've just commited the patch to the iptables git tree. The kernel patch is on its way upstream.