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Alter ipfw's behavior with respect to fragmented packets when the packet

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offset is non-zero:

  - Do not match fragmented packets if the rule specifies a port or
    TCP flags
  - Match fragmented packets if the rule does not specify a port and
    TCP flags

Since ipfw cannot examine port numbers or TCP flags for such packets,
it is now illegal to specify the 'frag' option with either ports or
tcpflags.  Both kernel and ipfw userland utility will reject rules
containing a combination of these options.

BEWARE: packets that were previously passed may now be rejected, and
vice versa.

Reviewed by:	Archie Cobbs <archie@whistle.com>
This commit is contained in:
Alexander Langer 1998-02-12 00:57:06 +00:00
parent 27f8f85b7e
commit ce78a1f6dd
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=33260
3 changed files with 62 additions and 5 deletions
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16
sbin/ipfw/ipfw.8
View File

@ -289,6 +289,12 @@ and the length of the port list is limited to
.Pa /usr/src/sys/netinet/ip_fw.h )
ports.
.Pp
Fragmented packets which have a non-zero offset (i.e. not the first
fragment) will never match a rule which has one or more port
specifications. See the
.Ar frag
option for details on matching fragmented packets.
.Pp
Rules can apply to packets when they are incoming, or outgoing, or both.
The
.Ar in
@ -360,6 +366,10 @@ Additional
.It frag
Matches if the packet is a fragment and this is not the first fragment
of the datagram.
.Ar frag
may not be used in conjunction with either
.Ar tcpflags
or TCP/UDP port specifications.
.It in
Matches if this packet was on the way in.
.It out
@ -399,6 +409,12 @@ and
.Ar urg .
The absence of a particular flag may be denoted
with a ``!''.
A rule which contains a
.Ar tcpflags
specification can never match a fragmented packet which has
a non-zero offset. See the
.Ar frag
option for details on matching fragmented packets.
.It icmptypes Ar types
Matches if the ICMP type is in the list
.Ar types .

13
sbin/ipfw/ipfw.c
View File

@ -16,7 +16,7 @@
*
* NEW command line interface for IP firewall facility
*
* $Id: ipfw.c,v 1.52 1998/01/08 00:27:31 alex Exp $
* $Id: ipfw.c,v 1.53 1998/01/08 03:03:50 alex Exp $
*
*/
@ -502,7 +502,7 @@ show_usage(const char *fmt, ...)
" src: from [not] {any|ip[{/bits|:mask}]} [{port|port-port},[port],...]\n"
" dst: to [not] {any|ip[{/bits|:mask}]} [{port|port-port},[port],...]\n"
" extras:\n"
" fragment\n"
" fragment (may not be used with ports or tcpflags)\n"
" in\n"
" out\n"
" {xmit|recv|via} {iface|ip|any}\n"
@ -1108,6 +1108,15 @@ add(ac,av)
} else if ((rule.fw_flg & IP_FW_F_OIFACE) && (rule.fw_flg & IP_FW_F_IN))
show_usage("can't check xmit interface of incoming packets");
/* frag may not be used in conjunction with ports or TCP flags */
if (rule.fw_flg & IP_FW_F_FRAG) {
if (rule.fw_tcpf || rule.fw_tcpnf)
show_usage(EX_USAGE, "can't mix 'frag' and tcpflags");
if (rule.fw_nports)
show_usage(EX_USAGE, "can't mix 'frag' and port specifications");
}
if (!do_quiet)
show_ipfw(&rule, 10, 10);
i = setsockopt(s, IPPROTO_IP, IP_FW_ADD, &rule, sizeof rule);

38
sys/netinet/ip_fw.c
View File

@ -12,7 +12,7 @@
*
* This software is provided ``AS IS'' without any warranties of any kind.
*
* $Id: ip_fw.c,v 1.76 1998/02/06 12:13:51 eivind Exp $
* $Id: ip_fw.c,v 1.77 1998/02/09 06:10:10 eivind Exp $
*/
/*
@ -459,8 +459,18 @@ ip_fw_chk(struct ip **pip, int hlen,
if (offset == 1) /* cf. RFC 1858 */
goto bogusfrag;
if (offset != 0) /* Flags, ports aren't valid */
if (offset != 0) {
/*
* TCP flags and ports aren't available in this
* packet -- if this rule specified either one,
* we consider the rule a non-match.
*/
if (f->fw_nports != 0 ||
f->fw_tcpf != f->fw_tcpnf)
continue;
break;
}
PULLUP_TO(hlen + 14);
tcp = (struct tcphdr *) ((u_long *)ip + ip->ip_hl);
if (f->fw_tcpf != f->fw_tcpnf && !tcpflg_match(tcp, f))
@ -474,8 +484,17 @@ ip_fw_chk(struct ip **pip, int hlen,
{
struct udphdr *udp;
if (offset != 0) /* Ports aren't valid */
if (offset != 0) {
/*
* Port specification is unavailable -- if this
* rule specifies a port, we consider the rule
* a non-match.
*/
if (f->fw_nports != 0)
continue;
break;
}
PULLUP_TO(hlen + 4);
udp = (struct udphdr *) ((u_long *)ip + ip->ip_hl);
src_port = ntohs(udp->uh_sport);
@ -868,6 +887,19 @@ check_ipfw_struct(struct ip_fw *frwl)
return(NULL);
}
if ((frwl->fw_flg & IP_FW_F_FRAG) &&
(frwl->fw_prot == IPPROTO_UDP || frwl->fw_prot == IPPROTO_TCP)) {
if (frwl->fw_nports) {
dprintf(("%s cannot mix 'frag' and ports\n", err_prefix));
return(NULL);
}
if (frwl->fw_prot == IPPROTO_TCP &&
frwl->fw_tcpf != frwl->fw_tcpnf) {
dprintf(("%s cannot mix 'frag' and TCP flags\n", err_prefix));
return(NULL);
}
}
/* Check command specific stuff */
switch (frwl->fw_flg & IP_FW_F_COMMAND)
{