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

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Date: Wed, 6 Mar 2024 15:55:45 +0100
From: Eric Dumazet <edumazet@...gle.com>
To: Jason Xing <kerneljasonxing@...il.com>
Cc: Paolo Abeni <pabeni@...hat.com>, Gavrilov Ilia <Ilia.Gavrilov@...otecs.ru>, 
	"David S. Miller" <davem@...emloft.net>, David Ahern <dsahern@...nel.org>, 
	Jakub Kicinski <kuba@...nel.org>, "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] tcp: fix incorrect parameter validation in the
 do_tcp_getsockopt() function

On Wed, Mar 6, 2024 at 12:57 PM Jason Xing <kerneljasonxing@...il.com> wrote:
>
> Hello Paolo,
>
> On Wed, Mar 6, 2024 at 7:36 PM Paolo Abeni <pabeni@...hat.com> wrote:
> >
> > On Wed, 2024-03-06 at 09:57 +0000, Gavrilov Ilia wrote:
> > > The 'len' variable can't be negative because all 'min_t' parameters
> > > cast to unsigned int, and then the minimum one is chosen.
> >
> > The above is incorrect, as the 'len' variable is a signed integer
>
> The 'len' variable should be converted to the non-negative value as
> this sentence:
>
> len = min_t(unsigned int, len, sizeof(int));
>
> See the comments of min_t(): return minimum of two values, using the
> specified type.
>
> After executing the above code, it doesn't make sense to test if 'len
> < 0', I think.

This is essentially dead (defensive ?) code.

Most compilers optimize this completely, no big deal.