[net,v2] netfilter: nat: fix ICMP header corruption on ICMP errors

[net,v2] netfilter: nat: fix ICMP header corruption on ICMP errors

[Eyal Birger]

Commit 8303b7e8f018 ("netfilter: nat: fix spurious connection timeouts")
made nf_nat_icmp_reply_translation() use icmp_manip_pkt() as the l4
manipulation function for the outer packet on ICMP errors.

However, icmp_manip_pkt() assumes the packet has an 'id' field which
is not correct for all types of ICMP messages.

This is not correct for ICMP error packets, and leads to bogus bytes
being written the ICMP header, which can be wrongfully regarded as
'length' bytes by RFC 4884 compliant receivers.

Fix by assigning the 'id' field only for ICMP messages that have this
semantic.

Reported-by: Shmulik Ladkani <shmulik.ladkani@gmail.com>
Fixes: 8303b7e8f018 ("netfilter: nat: fix spurious connection timeouts")
Signed-off-by: Eyal Birger <eyal.birger@gmail.com>

---
v1->v2 apply id field to all relevant ICMP messages
---
 net/netfilter/nf_nat_proto.c | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/net/netfilter/nf_nat_proto.c b/net/netfilter/nf_nat_proto.c
index 0a59c14b5177..64eedc17037a 100644
--- a/net/netfilter/nf_nat_proto.c
+++ b/net/netfilter/nf_nat_proto.c
@@ -233,6 +233,19 @@ icmp_manip_pkt(struct sk_buff *skb,
 		return false;
 
 	hdr = (struct icmphdr *)(skb->data + hdroff);
+	switch (hdr->type) {
+	case ICMP_ECHO:
+	case ICMP_ECHOREPLY:
+	case ICMP_TIMESTAMP:
+	case ICMP_TIMESTAMPREPLY:
+	case ICMP_INFO_REQUEST:
+	case ICMP_INFO_REPLY:
+	case ICMP_ADDRESS:
+	case ICMP_ADDRESSREPLY:
+		break;
+	default:
+		return true;
+	}
 	inet_proto_csum_replace2(&hdr->checksum, skb,
 				 hdr->un.echo.id, tuple->src.u.icmp.id, false);
 	hdr->un.echo.id = tuple->src.u.icmp.id;
-- 
2.20.1

Re: [net,v2] netfilter: nat: fix ICMP header corruption on ICMP errors

[Florian Westphal]

Eyal Birger <eyal.birger@gmail.com> wrote:
> Commit 8303b7e8f018 ("netfilter: nat: fix spurious connection timeouts")
> made nf_nat_icmp_reply_translation() use icmp_manip_pkt() as the l4
> manipulation function for the outer packet on ICMP errors.
> 
> However, icmp_manip_pkt() assumes the packet has an 'id' field which
> is not correct for all types of ICMP messages.
> 
> This is not correct for ICMP error packets, and leads to bogus bytes
> being written the ICMP header, which can be wrongfully regarded as
> 'length' bytes by RFC 4884 compliant receivers.
> 
> Fix by assigning the 'id' field only for ICMP messages that have this
> semantic.

Looks good, thanks Eyal.

Acked-by: Florian Westphal <fw@strlen.de>

Re: [net,v2] netfilter: nat: fix ICMP header corruption on ICMP errors

[Pablo Neira Ayuso]

On Tue, Jan 14, 2020 at 10:03:50AM +0200, Eyal Birger wrote:
> Commit 8303b7e8f018 ("netfilter: nat: fix spurious connection timeouts")
> made nf_nat_icmp_reply_translation() use icmp_manip_pkt() as the l4
> manipulation function for the outer packet on ICMP errors.
> 
> However, icmp_manip_pkt() assumes the packet has an 'id' field which
> is not correct for all types of ICMP messages.
> 
> This is not correct for ICMP error packets, and leads to bogus bytes
> being written the ICMP header, which can be wrongfully regarded as
> 'length' bytes by RFC 4884 compliant receivers.
> 
> Fix by assigning the 'id' field only for ICMP messages that have this
> semantic.

Applied, thanks.