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Date: Wed, 6 Mar 2024 14:32:59 +0000
From: Tom Parkin <tparkin@katalix.com>
To: Gavrilov Ilia <Ilia.Gavrilov@infotecs.ru>
Cc: James Chapman <jchapman@katalix.com>,
	"David S. Miller" <davem@davemloft.net>,
	Eric Dumazet <edumazet@google.com>,
	Jakub Kicinski <kuba@kernel.org>, Paolo Abeni <pabeni@redhat.com>,
	"netdev@vger.kernel.org" <netdev@vger.kernel.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"lvc-project@linuxtesting.org" <lvc-project@linuxtesting.org>
Subject: Re: [PATCH net-next] l2tp: fix incorrect parameter validation in the
 pppol2tp_getsockopt() function
Message-ID: <Zeh+m84IESlWU1rE@katalix.com>
References: <20240306095449.1782369-1-Ilia.Gavrilov@infotecs.ru>
 <ZehsL8sHd3vgplv1@katalix.com>
 <c9dd0486-aacc-4263-bcce-630fad445e72@infotecs.ru>
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On  Wed, Mar 06, 2024 at 13:46:07 +0000, Gavrilov Ilia wrote:
> On 3/6/24 16:14, Tom Parkin wrote:
> > As it stands right now in the l2tp_ppp.c code, I think the check on
> > len will end up doing nothing, as you point out.
> >=20
> > So moving the len check to before the min_t() call may in theory
> > possibly catch out (insane?) userspace code passing in negative
> > numbers which may "work" with the current kernel code.
> >=20
> > I wonder whether its safer therefore to remove the len check
> > altogether?
>=20
> Thank you for answer.
>=20
> In my opinion, it is better to leave the 'len' check. This way it will=20
> be easier for the user to understand where the error is.

Fair enough.

My concern was that in doing so we add a new behaviour which userspace
may notice and care about, but realistically I'm probably being
paranoid to imagine that any such userspace exists.

Thanks for your work on l2tp_ppp.c :-)

Reviewed-by: Tom Parkin <tparkin@katalix.com>

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