[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-ID: <ZehsL8sHd3vgplv1@katalix.com>
Date: Wed, 6 Mar 2024 13:14:23 +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 09:58:10 +0000, Gavrilov Ilia wrote:
> diff --git a/net/l2tp/l2tp_ppp.c b/net/l2tp/l2tp_ppp.c
> index f011af6601c9..6146e4e67bbb 100644
> --- a/net/l2tp/l2tp_ppp.c
> +++ b/net/l2tp/l2tp_ppp.c
> @@ -1356,11 +1356,11 @@ static int pppol2tp_getsockopt(struct socket *sock, int level, int optname,
> if (get_user(len, optlen))
> return -EFAULT;
>
> - len = min_t(unsigned int, len, sizeof(int));
> -
> if (len < 0)
> return -EINVAL;
>
> + len = min_t(unsigned int, len, sizeof(int));
> +
> err = -ENOTCONN;
> if (!sk->sk_user_data)
> goto end;
I think this code in l2tp_ppp.c has probably been inspired by a
similar implementations elsewhere in the kernel -- for example
net/ipv4/udp.c udp_lib_getsockopt does the same thing, and apparently
has been that way since the dawn of git time.
I note however that plenty of other getsockopt implementations which
are using min_t(unsigned int, len, sizeof(int)) don't check the length
value at all: as an example, net/ipv6/raw.c do_rawv6_getsockopt.
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?
--
Tom Parkin
Katalix Systems Ltd
https://katalix.com
Catalysts for your Embedded Linux software development
Download attachment "signature.asc" of type "application/pgp-signature" (489 bytes)
Powered by blists - more mailing lists