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Message-ID: <87mvrvwz72.fsf@x220.int.ebiederm.org>
Date: Sat, 23 Jan 2016 19:20:17 -0600
From: ebiederm@...ssion.com (Eric W. Biederman)
To: Jann Horn <jann@...jh.net>
Cc: kernel-hardening@...ts.openwall.com, Kees Cook <keescook@...omium.org>,
Andrew Morton <akpm@...ux-foundation.org>, Al Viro
<viro@...iv.linux.org.uk>, Richard Weinberger <richard@....at>, Andy
Lutomirski <luto@...capital.net>, Robert Święcki
<robert@...ecki.net>, Dmitry Vyukov <dvyukov@...gle.com>, David Howells
<dhowells@...hat.com>, Miklos Szeredi <mszeredi@...e.cz>, Kostya
Serebryany <kcc@...gle.com>, Alexander Potapenko <glider@...gle.com>,
Eric Dumazet <edumazet@...gle.com>, Sasha Levin
<sasha.levin@...cle.com>, linux-doc@...r.kernel.org,
linux-kernel@...r.kernel.org
Subject: Re: Re: [PATCH 1/2] sysctl: expand use of proc_dointvec_minmax_sysadmin
Jann Horn <jann@...jh.net> writes:
> On Fri, Jan 22, 2016 at 09:10:07PM -0600, Eric W. Biederman wrote:
>> Kees Cook <keescook@...omium.org> writes:
>>
>> > Several sysctls expect a state where the highest value (in extra2) is
>> > locked once set for that boot. Yama does this, and kptr_restrict should
>> > be doing it. This extracts Yama's logic and adds it to the existing
>> > proc_dointvec_minmax_sysadmin, taking care to avoid the simple boolean
>> > states (which do not get locked). Since Yama wants to be checking a
>> > different capability, we build wrappers for both cases (CAP_SYS_ADMIN
>> > and CAP_SYS_PTRACE).
>>
>> Sigh this sysctl appears susceptible to known attacks.
>>
>> In my quick skim I believe this sysctl implementation that checks
>> capabilities is susceptible to attacks where the already open file
>> descriptor is set as stdout on a setuid root application.
>>
>> Can we come up with an interface that isn't exploitable by an
>> application that will act as a setuid cat?
>
> Adding the struct file * to the parameters of all proc_handler
> functions would work, right? (Or just filp->f_cred? That would be
> less generic.)
>
> A quick grep says that's just about 160 functions that'll need to
> be changed. :/
Yep. That is about the size of it. file * used to be passed to the
sysctl methods but it was removed several years ago because no one was
using it.
Eric
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