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SubjectRe: iptables and tcpdump
On Mon, 29 Oct 2001 21:31:57 -0800 (PST)
"David S. Miller" <davem@redhat.com> wrote:

> From: Rusty Russell <rusty@rustcorp.com.au>
> Date: Tue, 30 Oct 2001 15:28:12 +1100
>
> should the NAT layer be doing skb_unshare() before altering the packet?
>
> I think it should.

Agreed. The 2.2 masq code didn't do this, and hence the "don't tcpdump on masq host"
recommendation.

Please try this patch (compiles at least),
Rusty.

diff -urN -I \$.*\$ --exclude TAGS -X /home/rusty/devel/kernel/kernel-patches/current-dontdiff --minimal linux-2.4.13-official/net/ipv4/netfilter/ip_fw_compat.c working-2.4.13-nfunshare/net/ipv4/netfilter/ip_fw_compat.c
--- linux-2.4.13-official/net/ipv4/netfilter/ip_fw_compat.c Sat Apr 28 07:15:01 2001
+++ working-2.4.13-nfunshare/net/ipv4/netfilter/ip_fw_compat.c Wed Oct 31 17:05:53 2001
@@ -78,11 +78,19 @@
{
int ret = FW_BLOCK;
u_int16_t redirpt;
+ struct sk_buff *nskb;

/* Assume worse case: any hook could change packet */
(*pskb)->nfcache |= NFC_UNKNOWN | NFC_ALTERED;
if ((*pskb)->ip_summed == CHECKSUM_HW)
(*pskb)->ip_summed = CHECKSUM_NONE;
+
+ /* Firewall rules can alter TOS: raw socket may have clone of
+ skb: don't disturb it --RR */
+ nskb = skb_unshare(*pskb, GFP_ATOMIC);
+ if (!nskb)
+ return NF_DROP;
+ *pskb = nskb;

switch (hooknum) {
case NF_IP_PRE_ROUTING:
diff -urN -I \$.*\$ --exclude TAGS -X /home/rusty/devel/kernel/kernel-patches/current-dontdiff --minimal linux-2.4.13-official/net/ipv4/netfilter/ip_nat_core.c working-2.4.13-nfunshare/net/ipv4/netfilter/ip_nat_core.c
--- linux-2.4.13-official/net/ipv4/netfilter/ip_nat_core.c Thu May 17 03:31:27 2001
+++ working-2.4.13-nfunshare/net/ipv4/netfilter/ip_nat_core.c Wed Oct 31 16:52:06 2001
@@ -734,6 +734,15 @@
synchronize_bh()) can vanish. */
READ_LOCK(&ip_nat_lock);
for (i = 0; i < info->num_manips; i++) {
+ struct sk_buff *nskb;
+ /* raw socket may have clone of skb: don't disturb it --RR */
+ nskb = skb_unshare(*pskb, GFP_ATOMIC);
+ if (!nskb) {
+ READ_UNLOCK(&ip_nat_lock);
+ return NF_DROP;
+ }
+ *pskb = nskb;
+
if (info->manips[i].direction == dir
&& info->manips[i].hooknum == hooknum) {
DEBUGP("Mangling %p: %s to %u.%u.%u.%u %u\n",
diff -urN -I \$.*\$ --exclude TAGS -X /home/rusty/devel/kernel/kernel-patches/current-dontdiff --minimal linux-2.4.13-official/net/ipv4/netfilter/ipt_TCPMSS.c working-2.4.13-nfunshare/net/ipv4/netfilter/ipt_TCPMSS.c
--- linux-2.4.13-official/net/ipv4/netfilter/ipt_TCPMSS.c Mon Oct 1 05:26:08 2001
+++ working-2.4.13-nfunshare/net/ipv4/netfilter/ipt_TCPMSS.c Wed Oct 31 17:00:42 2001
@@ -48,6 +48,13 @@
u_int16_t tcplen, newtotlen, oldval, newmss;
unsigned int i;
u_int8_t *opt;
+ struct sk_buff *nskb;
+
+ /* raw socket may have clone of skb: don't disturb it --RR */
+ nskb = skb_unshare(*pskb, GFP_ATOMIC);
+ if (!nskb)
+ return NF_DROP;
+ *pskb = nskb;

tcplen = (*pskb)->len - iph->ihl*4;

diff -urN -I \$.*\$ --exclude TAGS -X /home/rusty/devel/kernel/kernel-patches/current-dontdiff --minimal linux-2.4.13-official/net/ipv4/netfilter/ipt_TOS.c working-2.4.13-nfunshare/net/ipv4/netfilter/ipt_TOS.c
--- linux-2.4.13-official/net/ipv4/netfilter/ipt_TOS.c Mon Oct 1 05:26:08 2001
+++ working-2.4.13-nfunshare/net/ipv4/netfilter/ipt_TOS.c Wed Oct 31 17:03:11 2001
@@ -19,7 +19,14 @@
const struct ipt_tos_target_info *tosinfo = targinfo;

if ((iph->tos & IPTOS_TOS_MASK) != tosinfo->tos) {
+ struct sk_buff *nskb;
u_int16_t diffs[2];
+
+ /* raw socket may have clone of skb: don't disturb it --RR */
+ nskb = skb_unshare(*pskb, GFP_ATOMIC);
+ if (!nskb)
+ return NF_DROP;
+ *pskb = nskb;

diffs[0] = htons(iph->tos) ^ 0xFFFF;
iph->tos = (iph->tos & IPTOS_PREC_MASK) | tosinfo->tos;
-
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