linux-kernel - Re: [PATCH net-next] l2tp: fix incorrect parameter validation in the pppol2tp

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Date: Wed, 6 Mar 2024 14:32:59 +0000
From: Tom Parkin <tparkin@...alix.com>
To: Gavrilov Ilia <Ilia.Gavrilov@...otecs.ru>
Cc: James Chapman <jchapman@...alix.com>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"lvc-project@...uxtesting.org" <lvc-project@...uxtesting.org>
Subject: Re: [PATCH net-next] l2tp: fix incorrect parameter validation in the
 pppol2tp_getsockopt() function

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.
> > 
> > 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.
> > 
> > I wonder whether its safer therefore to remove the len check
> > altogether?
> 
> Thank you for answer.
> 
> In my opinion, it is better to leave the 'len' check. This way it will 
> 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@...alix.com>

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