netdev - Re: [Patch net] mlx5: check for malformed packets

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Date:   Tue, 4 Dec 2018 12:21:42 -0800
From:   Cong Wang <xiyou.wangcong@...il.com>
To:     saeedm@....mellanox.co.il
Cc:     Linux Kernel Network Developers <netdev@...r.kernel.org>,
        Tariq Toukan <tariqt@...lanox.com>,
        Saeed Mahameed <saeedm@...lanox.com>
Subject: Re: [Patch net] mlx5: check for malformed packets

On Tue, Dec 4, 2018 at 11:33 AM Saeed Mahameed
<saeedm@....mellanox.co.il> wrote:
>
> On Sat, Dec 1, 2018 at 12:38 PM Cong Wang <xiyou.wangcong@...il.com> wrote:
> >
> > is_last_ethertype_ip() is used to check IP/IPv6 protocol before
> > parsing IP/IPv6 headers.
> >
> > But __vlan_get_protocol() is only bound to skb->len, a malicious
> > packet could exhaust all skb->len by inserting sufficient ETH_P_8021AD
> > headers, and it may not even contain an IP/IPv6 header at all, so we
> > have to check if we are still safe to continue to parse IP/IPv6 header.
> > If not, treat it as non-IP packet.
> >
> > This should not cause any crash as we stil have tail room in skb,
> > but we can't just rely on it either.
>
> Hi Cong, is this reproducible or just a theory ? which part of the
> code you think will cause the invalid access or crash ?

Since you don't even read into my changelog, here it is:

"This should not cause any crash as we stil have tail room in skb,
but we can't just rely on it either."

As I already explained to you in a private email, when we
reference whatever field in struct iphdr, we have to make sure
the offset of that field is within skb->len.


> do you have steps to reproduce this?
>

Again, you really have to read the changelog I wrote:


"a malicious
packet could exhaust all skb->len by inserting sufficient ETH_P_8021AD
headers, and it may not even contain an IP/IPv6 header at all, "


> I would like to investigate this myself, it will take a couple of days
> if that's ok with you ..

Sure, take your time. I am sending the patch only for showing
the problem, NOT to merge.


Let's discard it anyway. I am wasting my time.

Thanks.