netdev - Re: IP oversized ip oacket from - header size should be skipped?

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Date: Fri, 28 Jun 2024 12:36:08 +0200
From: Ian Kumlien <ian.kumlien@...il.com>
To: Linux Kernel Network Developers <netdev@...r.kernel.org>
Subject: Re: IP oversized ip oacket from - header size should be skipped?

On Fri, Jun 28, 2024 at 11:30 AM Ian Kumlien <ian.kumlien@...il.com> wrote:
>
> Hi,
>
> In net/ipv4/ip_fragment.c line 412:
> static int ip_frag_reasm(struct ipq *qp, struct sk_buff *skb,
>                          struct sk_buff *prev_tail, struct net_device *dev)
> {
> ...
>         len = ip_hdrlen(skb) + qp->q.len;
>         err = -E2BIG;
>         if (len > 65535)
>                 goto out_oversize;
> ....
>
> We can expand the expression to:
> len = (ip_hdr(skb)->ihl * 4) + qp->q.len;
>
> But it's still weird since the definition of q->len is: "total length
> of the original datagram"
> Which should mean that we are comparing total length + ip header size
> instead of just total length?

So something like this:
 git show 1fd2bd1e3335d0aa43e4ef2f55c7314f419026d7
commit 1fd2bd1e3335d0aa43e4ef2f55c7314f419026d7 (HEAD -> master)
Author: Ian Kumlien <ian.kumlien@...il.com>
Date:   Fri Jun 28 12:30:24 2024 +0200

    Omit extra ip header from calculation

    Remove extra ip header from calculation of the
    total length of the IP packet.

    Fixes: c23f35d19db3b36ffb9e04b08f1d91565d15f84f
    Signed-off-by: Ian KUmlien <ian.kumlien@...il.com>

diff --git a/net/ipv4/ip_fragment.c b/net/ipv4/ip_fragment.c
index 08e2c92e25ab..e55a771919d6 100644
--- a/net/ipv4/ip_fragment.c
+++ b/net/ipv4/ip_fragment.c
@@ -431,7 +431,7 @@ static int ip_frag_reasm(struct ipq *qp, struct
sk_buff *skb,
        if (!reasm_data)
                goto out_nomem;

-       len = ip_hdrlen(skb) + qp->q.len;
+       len = qp->q.len;
        err = -E2BIG;
        if (len > 65535)
                goto out_oversize;