Re: [PATCH]: invaild TCP/UDP matching when ipv6 extension header exists

[Yasuyuki Kozakai <yasuyuki.kozakai@xxxxxxxxxxxxx>]

Hello,

I sent the patch which fixes this bug to netfilter-devel, but it include
other bug... sorry, I rewrite patch for ip6_tables.c .

Please don't forget apply the patch which fixes the bug in ipv6_skip_exthdr()
before you tests this patch. I sent it last few minutes to netdev and
netfilter-devel.

Regards,

-----------------------------------------------------------------
Yasuyuki KOZAKAI @ USAGI Project <yasuyuki.kozakai@xxxxxxxxxxxxx>


From: Yasuyuki Kozakai <yasuyuki.kozakai@xxxxxxxxxxxxx>
Subject: [PATCH]: invaild TCP/UDP matching when ipv6 extension header exists
Date: Sat, 31 Jan 2004 15:49:32 +0900 (JST)


> Hi,
> 
> tcp_match() and udp_match() in ip6tables.c assume that previous header
> of TCP/UDP header is IPv6 Header. So, for example, 1st of fragmented UDP
> packet, AHed packets can't correctly match the rules which use
> "--sport" and so on.
> 
> This patch use ipv6_skip_exthdr() . But this function has the bug which
> access invalid memory area when found Fragment Header.
> So this patch includes the change for that, too.
> 
> Regards,

diff -Nur linux-2.6.3/net/ipv6/ipv6_syms.c 
linux-2.6.3-fixed/net/ipv6/ipv6_syms.c
--- linux-2.6.3/net/ipv6/ipv6_syms.c    2004-02-18 12:58:48.000000000 +0900
+++ linux-2.6.3-fixed/net/ipv6/ipv6_syms.c      2004-02-19 19:11:12.000000000 
+0900
@@ -46,3 +46,4 @@
 EXPORT_SYMBOL(ip6_flush_pending_frames);
 EXPORT_SYMBOL(ip6_push_pending_frames);
 EXPORT_SYMBOL(ipv6_push_nfrag_opts);
+EXPORT_SYMBOL(ipv6_skip_exthdr);
diff -Nur linux-2.6.3/net/ipv6/netfilter/ip6_tables.c 
linux-2.6.3-fixed/net/ipv6/netfilter/ip6_tables.c
--- linux-2.6.3/net/ipv6/netfilter/ip6_tables.c 2004-02-18 12:59:22.000000000 
+0900
+++ linux-2.6.3-fixed/net/ipv6/netfilter/ip6_tables.c   2004-02-20 
12:39:48.155754688 +0900
@@ -1570,8 +1570,10 @@
          u_int16_t datalen,
          int *hotdrop)
 {
-       const struct tcphdr *tcp = hdr;
+       const struct tcphdr *tcp;
        const struct ip6t_tcp *tcpinfo = matchinfo;
+       int tcpoff;
+       u8 nexthdr = skb->nh.ipv6h->nexthdr;
 
        /* To quote Alan:
 
@@ -1592,6 +1594,24 @@
                return 0;
        }
 
+       tcpoff = (u8*)(skb->nh.ipv6h + 1) - skb->data;
+       tcpoff = ipv6_skip_exthdr(skb, tcpoff, &nexthdr, skb->len - tcpoff);
+       if (tcpoff < 0 || tcpoff > skb->len) {
+               duprintf("tcp_match: cannot skip exthdr. Dropping.\n");
+               *hotdrop = 1;
+               return 0;
+       } else if (nexthdr == IPPROTO_FRAGMENT)
+               return 0;
+       else if (nexthdr != IPPROTO_TCP ||
+                skb->len - tcpoff < sizeof(struct tcphdr)) {
+               /* cannot be occured */
+               duprintf("tcp_match: cannot get TCP header. Dropping.\n");
+               *hotdrop = 1;
+               return 0;
+       }
+
+       tcp = (struct tcphdr *)(skb->data + tcpoff);
+
        /* FIXME: Try tcp doff >> packet len against various stacks --RR */
 
 #define FWINVTCP(bool,invflg) ((bool) ^ !!(tcpinfo->invflags & invflg))
@@ -1642,8 +1662,10 @@
          u_int16_t datalen,
          int *hotdrop)
 {
-       const struct udphdr *udp = hdr;
+       const struct udphdr *udp;
        const struct ip6t_udp *udpinfo = matchinfo;
+       int udpoff;
+       u8 nexthdr = skb->nh.ipv6h->nexthdr;
 
        if (offset == 0 && datalen < sizeof(struct udphdr)) {
                /* We've been asked to examine this packet, and we
@@ -1653,6 +1675,23 @@
                return 0;
        }
 
+       udpoff = (u8*)(skb->nh.ipv6h + 1) - skb->data;
+       udpoff = ipv6_skip_exthdr(skb, udpoff, &nexthdr, skb->len - udpoff);
+       if (udpoff < 0 || udpoff > skb->len) {
+               duprintf("udp_match: cannot skip exthdr. Dropping.\n");
+               *hotdrop = 1;
+               return 0;
+       } else if (nexthdr == IPPROTO_FRAGMENT)
+               return 0;
+       else if (nexthdr != IPPROTO_UDP ||
+                skb->len - udpoff < sizeof(struct udphdr)) {
+               duprintf("udp_match: cannot get UDP header. Dropping.\n");
+               *hotdrop = 1;
+               return 0;
+       }
+
+       udp = (struct udphdr *)(skb->data + udpoff);
+
        /* Must not be a fragment. */
        return !offset
                && port_match(udpinfo->spts[0], udpinfo->spts[1],