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Netfilter Core Team Security Advisory
=20
CVE: CAN-2003-0187
Subject:
Netfilter / Connection Tracking Remote DoS
Released:
01 Aug 2003
Effects:
Any remote user may be able to DoS a machine with netfilter connection
tracking when running a specific version of the Linux kernel.
Estimated Severity:
High.
Systems Affected:
Linux 2.4.20 kernels (kernels <=3D 2.4.19 and >=3D 2.4.21 NOT affected)
CONFIG_IP_NF_CONNTRACK enabled, or the ip_conntrack module loaded.
Solution:
BEST: Upgrade to Linux kernels 2.4.21 (stable), or apply the patch below.
OR: Do not use connection tracking on 2.4.20 based systems.
Details:
The 2.4.20 kernel introduced a change in the behaviour of the generic
linked list support. The connection tracking core relies on the old
behaviour to identify 'UNCONFIRMED' connections. =20
=20
'UNCONFIRMED' means we've seen traffic only in one direction, but not
in the other. Since connection tracking was unable to identify such
connections correctly anymore, they've been assigned a very high
timeout.
The patch below changes the connection tracking core to no longer rely
on any specific behaviour of the linux linked listed API.
Vendor Statement:
Red Hat: Patches for this issue were first introduced in RHSA-2003:17
Others: unknown
Credits:
The problem was found, and the fix implemented by the Netfilter Core Team.
Contact:
coreteam@netfilter.org
diff -urN --exclude-from=3Ddiff.exclude linux-2.4.20-base/include/linux/net=
filter_ipv4/ip_conntrack.h linux-2.4.20-del/include/linux/netfilter_ipv4/ip=
_conntrack.h
--- linux-2.4.20-base/include/linux/netfilter_ipv4/ip_conntrack.h Fri Nov 2=
9 00:53:15 2002
+++ linux-2.4.20-del/include/linux/netfilter_ipv4/ip_conntrack.h Fri Feb 21=
17:01:38 2003
@@ -6,6 +6,7 @@
=20
#include <linux/config.h>
#include <linux/netfilter_ipv4/ip_conntrack_tuple.h>
+#include <linux/bitops.h>
#include <asm/atomic.h>
=20
enum ip_conntrack_info
@@ -41,6 +42,10 @@
/* Conntrack should never be early-expired. */
IPS_ASSURED_BIT =3D 2,
IPS_ASSURED =3D (1 << IPS_ASSURED_BIT),
+
+ /* Connection is confirmed: originating packet has left box */
+ IPS_CONFIRMED_BIT =3D 3,
+ IPS_CONFIRMED =3D (1 << IPS_CONFIRMED_BIT),
};
=20
#include <linux/netfilter_ipv4/ip_conntrack_tcp.h>
@@ -159,7 +164,7 @@
struct ip_conntrack_tuple_hash tuplehash[IP_CT_DIR_MAX];
=20
/* Have we seen traffic both ways yet? (bitset) */
- volatile unsigned long status;
+ unsigned long status;
=20
/* Timer function; drops refcnt when it goes off. */
struct timer_list timeout;
@@ -254,7 +259,7 @@
/* It's confirmed if it is, or has been in the hash table. */
static inline int is_confirmed(struct ip_conntrack *ct)
{
- return ct->tuplehash[IP_CT_DIR_ORIGINAL].list.next !=3D NULL;
+ return test_bit(IPS_CONFIRMED_BIT, &ct->status);
}
=20
extern unsigned int ip_conntrack_htable_size;
diff -urN --exclude-from=3Ddiff.exclude linux-2.4.20-base/net/ipv4/netfilte=
r/ip_conntrack_core.c linux-2.4.20-del/net/ipv4/netfilter/ip_conntrack_core=
=2Ec
--- linux-2.4.20-base/net/ipv4/netfilter/ip_conntrack_core.c Tue Feb 18 17:=
08:21 2003
+++ linux-2.4.20-del/net/ipv4/netfilter/ip_conntrack_core.c Fri Feb 21 17:0=
1:39 2003
@@ -292,9 +292,6 @@
{
DEBUGP("clean_from_lists(%p)\n", ct);
MUST_BE_WRITE_LOCKED(&ip_conntrack_lock);
- /* Remove from both hash lists: must not NULL out next ptrs,
- otherwise we'll look unconfirmed. Fortunately, LIST_DELETE
- doesn't do this. --RR */
LIST_DELETE(&ip_conntrack_hash
[hash_conntrack(&ct->tuplehash[IP_CT_DIR_ORIGINAL].tuple)],
&ct->tuplehash[IP_CT_DIR_ORIGINAL]);
@@ -467,6 +464,7 @@
ct->timeout.expires +=3D jiffies;
add_timer(&ct->timeout);
atomic_inc(&ct->ct_general.use);
+ set_bit(IPS_CONFIRMED_BIT, &ct->status);
WRITE_UNLOCK(&ip_conntrack_lock);
return NF_ACCEPT;
}
@@ -585,7 +583,7 @@
connection. Too bad: we're in trouble anyway. */
static inline int unreplied(const struct ip_conntrack_tuple_hash *i)
{
- return !(i->ctrack->status & IPS_ASSURED);
+ return !(test_bit(IPS_ASSURED_BIT, &i->ctrack->status));
}
=20
static int early_drop(struct list_head *chain)
@@ -720,7 +718,7 @@
conntrack, expected);
/* Welcome, Mr. Bond. We've been expecting you... */
IP_NF_ASSERT(master_ct(conntrack));
- conntrack->status =3D IPS_EXPECTED;
+ __set_bit(IPS_EXPECTED_BIT, &conntrack->status);
conntrack->master =3D expected;
expected->sibling =3D conntrack;
LIST_DELETE(&ip_conntrack_expect_list, expected);
@@ -768,11 +766,11 @@
*set_reply =3D 1;
} else {
/* Once we've had two way comms, always ESTABLISHED. */
- if (h->ctrack->status & IPS_SEEN_REPLY) {
+ if (test_bit(IPS_SEEN_REPLY_BIT, &h->ctrack->status)) {
DEBUGP("ip_conntrack_in: normal packet for %p\n",
h->ctrack);
*ctinfo =3D IP_CT_ESTABLISHED;
- } else if (h->ctrack->status & IPS_EXPECTED) {
+ } else if (test_bit(IPS_EXPECTED_BIT, &h->ctrack->status)) {
DEBUGP("ip_conntrack_in: related packet for %p\n",
h->ctrack);
*ctinfo =3D IP_CT_RELATED;
diff -urN --exclude-from=3Ddiff.exclude linux-2.4.20-base/net/ipv4/netfilte=
r/ip_conntrack_proto_tcp.c linux-2.4.20-del/net/ipv4/netfilter/ip_conntrack=
_proto_tcp.c
--- linux-2.4.20-base/net/ipv4/netfilter/ip_conntrack_proto_tcp.c Tue Feb 1=
8 17:07:26 2003
+++ linux-2.4.20-del/net/ipv4/netfilter/ip_conntrack_proto_tcp.c Fri Feb 21=
17:03:35 2003
@@ -192,7 +192,7 @@
have an established connection: this is a fairly common
problem case, so we can delete the conntrack
immediately. --RR */
- if (!(conntrack->status & IPS_SEEN_REPLY) && tcph->rst) {
+ if (!test_bit(IPS_SEEN_REPLY_BIT, &conntrack->status) && tcph->rst) {
WRITE_UNLOCK(&tcp_lock);
if (del_timer(&conntrack->timeout))
conntrack->timeout.function((unsigned long)conntrack);
diff -urN --exclude-from=3Ddiff.exclude linux-2.4.20-base/net/ipv4/netfilte=
r/ip_conntrack_proto_udp.c linux-2.4.20-del/net/ipv4/netfilter/ip_conntrack=
_proto_udp.c
--- linux-2.4.20-base/net/ipv4/netfilter/ip_conntrack_proto_udp.c Fri Nov 2=
9 00:53:15 2002
+++ linux-2.4.20-del/net/ipv4/netfilter/ip_conntrack_proto_udp.c Fri Feb 21=
17:01:39 2003
@@ -51,7 +51,7 @@
{
/* If we've seen traffic both ways, this is some kind of UDP
stream. Extend timeout. */
- if (conntrack->status & IPS_SEEN_REPLY) {
+ if (test_bit(IPS_SEEN_REPLY_BIT, &conntrack->status)) {
ip_ct_refresh(conntrack, UDP_STREAM_TIMEOUT);
/* Also, more likely to be important, and not a probe */
set_bit(IPS_ASSURED_BIT, &conntrack->status);
diff -urN --exclude-from=3Ddiff.exclude linux-2.4.20-base/net/ipv4/netfilte=
r/ip_conntrack_standalone.c linux-2.4.20-del/net/ipv4/netfilter/ip_conntrac=
k_standalone.c
--- linux-2.4.20-base/net/ipv4/netfilter/ip_conntrack_standalone.c Fri Nov =
29 00:53:15 2002
+++ linux-2.4.20-del/net/ipv4/netfilter/ip_conntrack_standalone.c Fri Feb 2=
1 21:10:37 2003
@@ -77,7 +77,7 @@
}
=20
static unsigned int
-print_conntrack(char *buffer, const struct ip_conntrack *conntrack)
+print_conntrack(char *buffer, struct ip_conntrack *conntrack)
{
unsigned int len;
struct ip_conntrack_protocol *proto
@@ -95,12 +95,12 @@
len +=3D print_tuple(buffer + len,
&conntrack->tuplehash[IP_CT_DIR_ORIGINAL].tuple,
proto);
- if (!(conntrack->status & IPS_SEEN_REPLY))
+ if (!(test_bit(IPS_SEEN_REPLY_BIT, &conntrack->status)))
len +=3D sprintf(buffer + len, "[UNREPLIED] ");
len +=3D print_tuple(buffer + len,
&conntrack->tuplehash[IP_CT_DIR_REPLY].tuple,
proto);
- if (conntrack->status & IPS_ASSURED)
+ if (test_bit(IPS_ASSURED_BIT, &conntrack->status))
len +=3D sprintf(buffer + len, "[ASSURED] ");
len +=3D sprintf(buffer + len, "use=3D%u ",
atomic_read(&conntrack->ct_general.use));
--
- Harald Welte <laforge@netfilter.org> http://www.netfilter.org/
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D
"Fragmentation is like classful addressing -- an interesting early
architectural error that shows how much experimentation was going
on while IP was being designed." -- Paul Vixie
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