2021-12-24 03:09:17

by kai zhang

Subject: [PATCH] netfilter: seqadj: check seq offset before update

if seq/ack offset is zero, don't update

Signed-off-by: zhang kai <[email protected]>
---
net/netfilter/nf_conntrack_seqadj.c | 15 ++++++++++-----
1 file changed, 10 insertions(+), 5 deletions(-)

diff --git a/net/netfilter/nf_conntrack_seqadj.c b/net/netfilter/nf_conntrack_seqadj.c
index 3066449f8bd8..d35e272a2e36 100644
--- a/net/netfilter/nf_conntrack_seqadj.c
+++ b/net/netfilter/nf_conntrack_seqadj.c
@@ -186,11 +186,13 @@ int nf_ct_seq_adjust(struct sk_buff *skb,
else
seqoff = this_way->offset_before;

- newseq = htonl(ntohl(tcph->seq) + seqoff);
- inet_proto_csum_replace4(&tcph->check, skb, tcph->seq, newseq, false);
- pr_debug("Adjusting sequence number from %u->%u\n",
- ntohl(tcph->seq), ntohl(newseq));
- tcph->seq = newseq;
+ if (seqoff) {
+ newseq = htonl(ntohl(tcph->seq) + seqoff);
+ inet_proto_csum_replace4(&tcph->check, skb, tcph->seq, newseq, false);
+ pr_debug("Adjusting sequence number from %u->%u\n",
+ ntohl(tcph->seq), ntohl(newseq));
+ tcph->seq = newseq;
+ }

if (!tcph->ack)
goto out;
@@ -201,6 +203,9 @@ int nf_ct_seq_adjust(struct sk_buff *skb,
else
ackoff = other_way->offset_before;

+ if (!ackoff)
+ goto out;
+
newack = htonl(ntohl(tcph->ack_seq) - ackoff);
inet_proto_csum_replace4(&tcph->check, skb, tcph->ack_seq, newack,
false);
--
2.17.1

2022-01-06 21:53:53

by Pablo Neira Ayuso

Subject: Re: [PATCH] netfilter: seqadj: check seq offset before update

On Fri, Dec 24, 2021 at 10:37:13AM +0800, zhang kai wrote:
> if seq/ack offset is zero, don't update

Please, provide more details: explain the scenario that triggers and
seq/ack offset adjustment of zero, describe the scenario that triggers
the bug, etc.

> Signed-off-by: zhang kai <[email protected]>
> ---
> net/netfilter/nf_conntrack_seqadj.c | 15 ++++++++++-----
> 1 file changed, 10 insertions(+), 5 deletions(-)
>
> diff --git a/net/netfilter/nf_conntrack_seqadj.c b/net/netfilter/nf_conntrack_seqadj.c
> index 3066449f8bd8..d35e272a2e36 100644
> --- a/net/netfilter/nf_conntrack_seqadj.c
> +++ b/net/netfilter/nf_conntrack_seqadj.c
> @@ -186,11 +186,13 @@ int nf_ct_seq_adjust(struct sk_buff *skb,
> else
> seqoff = this_way->offset_before;
>
> - newseq = htonl(ntohl(tcph->seq) + seqoff);
> - inet_proto_csum_replace4(&tcph->check, skb, tcph->seq, newseq, false);
> - pr_debug("Adjusting sequence number from %u->%u\n",
> - ntohl(tcph->seq), ntohl(newseq));
> - tcph->seq = newseq;
> + if (seqoff) {
> + newseq = htonl(ntohl(tcph->seq) + seqoff);
> + inet_proto_csum_replace4(&tcph->check, skb, tcph->seq, newseq, false);
> + pr_debug("Adjusting sequence number from %u->%u\n",
> + ntohl(tcph->seq), ntohl(newseq));
> + tcph->seq = newseq;
> + }
>
> if (!tcph->ack)
> goto out;
> @@ -201,6 +203,9 @@ int nf_ct_seq_adjust(struct sk_buff *skb,
> else
> ackoff = other_way->offset_before;
>
> + if (!ackoff)
> + goto out;
> +
> newack = htonl(ntohl(tcph->ack_seq) - ackoff);
> inet_proto_csum_replace4(&tcph->check, skb, tcph->ack_seq, newack,
> false);
> --
> 2.17.1
>