linux-kernel - Re: [PATCH] getsockopt() early argument sanity checking

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Date:	Sun, 20 Aug 2006 19:50:44 +0900 (JST)
From:	YOSHIFUJI Hideaki / 吉藤英明 
	<yoshfuji@...ux-ipv6.org>
To:	w@....eu
Cc:	ak@...e.de, solar@...nwall.com, linux-kernel@...r.kernel.org,
	netdev@...r.kernel.org, yoshfuji@...ux-ipv6.org
Subject: Re: [PATCH] getsockopt() early argument sanity checking

Hello.

In article <20060820101528.GE602@....eu> (at Sun, 20 Aug 2006 12:15:28 +0200), Willy Tarreau <w@....eu> says:

> But I don't want to induce such large changes in this kernel. The goal of
> this test is a preventive measure to catch easily exploitable errors that
> might have remained undetected. For instance, a quick glance shows this
> portion of code in net/ipv4/raw.c (both 2.4 and 2.6) :
> 
> static int raw_seticmpfilter(struct sock *sk, char *optval, int optlen)
> {
>         if (optlen > sizeof(struct icmp_filter))
>                 optlen = sizeof(struct icmp_filter);
>         if (copy_from_user(&sk->tp_pinfo.tp_raw4.filter, optval, optlen))
>                 return -EFAULT;
>         return 0;
> }
> 
> It only relies on sock_setsockopt() refusing optlen values < sizeof(int),
> and this is not documented. Having part of this code being copied for use
> in another code path would open a breach for optlen < 0.
:
> There are two tests in this patch :
> 
>   - one on the validity of the optlen address. This one is race-free and
>     should be conserved anyway.
> 
>   - one on the optlen range which is valid for most cases but which is
>     subject to a race condition and which might be circumvented by
>     carefully written code and with some luck as in all race conditions
>     issues.

Don't mix getsockopt() and setsockopt() code paths.

For setsockopt(), optlen < 0 is checked in net/socket.c:sys_setsockopt().

For getsockopt(), optlen and *optlen < 0 is (and should be) checked
(or handled) in each getsockopt function; e.g. do_ip_getsockopt(),
raw_geticmpfilter() etc.

--yoshfuji
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