From: Tom Parkin <tparkin@katalix.com>
To: Jakub Kicinski <kuba@kernel.org>
Cc: Matthias Schiffer <mschiffer@universe-factory.net>,
netdev@vger.kernel.org, "David S. Miller" <davem@davemloft.net>,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH net] net: l2tp: reduce log level when passing up invalid packets
Date: Tue, 23 Feb 2021 09:47:22 +0000 [thread overview]
Message-ID: <20210223094722.GB12377@katalix.com> (raw)
In-Reply-To: <20210222143138.5711048a@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com>
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On Mon, Feb 22, 2021 at 14:31:38 -0800, Jakub Kicinski wrote:
> On Mon, 22 Feb 2021 17:40:16 +0100 Matthias Schiffer wrote:
> > >> This will not be sufficient for my usecase: To stay compatible with older
> > >> versions of fastd, I can't set the T flag in the first packet of the
> > >> handshake, as it won't be known whether the peer has a new enough fastd
> > >> version to understand packets that have this bit set. Luckily, the second
> > >> handshake byte is always 0 in fastd's protocol, so these packets fail the
> > >> tunnel version check and are passed to userspace regardless.
> > >>
> > >> I'm aware that this usecase is far outside of the original intentions of the
> > >> code and can only be described as a hack, but I still consider this a
> > >> regression in the kernel, as it was working fine in the past, without
> > >> visible warnings.
> > >>
> > >
> > > I'm sorry, but for the reasons stated above I disagree about it being
> > > a regression.
> >
> > Hmm, is it common for protocol implementations in the kernel to warn about
> > invalid packets they receive? While L2TP uses connected sockets and thus
> > usually no unrelated packets end up in the socket, a simple UDP port scan
> > originating from the configured remote address/port will trigger the "short
> > packet" warning now (nmap uses a zero-length payload for UDP scans by
> > default). Log spam caused by a malicous party might also be a concern.
>
> Indeed, seems like appropriate counters would be a good fit here?
> The prints are both potentially problematic for security and lossy.
Yes, I agree with this argument.
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next prev parent reply other threads:[~2021-02-23 9:49 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-02-19 19:06 [PATCH net] net: l2tp: reduce log level when passing up invalid packets Matthias Schiffer
2021-02-19 20:12 ` Tom Parkin
2021-02-20 9:56 ` Matthias Schiffer
2021-02-22 11:49 ` Tom Parkin
2021-02-22 16:40 ` Matthias Schiffer
2021-02-22 22:31 ` Jakub Kicinski
2021-02-23 9:47 ` Tom Parkin [this message]
2021-03-01 23:23 ` Matthias Schiffer
2021-02-23 9:46 ` Tom Parkin
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