From: Andy Lutomirski <luto@amacapital.net>
To: Ben Hutchings <ben@decadent.org.uk>
Cc: Andy Lutomirski <luto@kernel.org>,
"security@kernel.org" <security@kernel.org>,
Konstantin Khlebnikov <koct9i@gmail.com>,
Alexander Viro <viro@zeniv.linux.org.uk>,
Kees Cook <keescook@chromium.org>, Willy Tarreau <w@1wt.eu>,
"linux-mm@kvack.org" <linux-mm@kvack.org>,
Andrew Morton <akpm@linux-foundation.org>,
yalin wang <yalin.wang2010@gmail.com>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Jan Kara <jack@suse.cz>,
Linux FS Devel <linux-fsdevel@vger.kernel.org>,
stable <stable@vger.kernel.org>
Subject: Re: [PATCH 1/2] fs: Check f_cred instead of current's creds in should_remove_suid()
Date: Wed, 25 Jan 2017 13:48:19 -0800 [thread overview]
Message-ID: <CALCETrUyWGF7WWVxv5e1tznkdV07YCrOcUeoJE8wUn-qCZMAKw@mail.gmail.com> (raw)
In-Reply-To: <1485380634.2998.161.camel@decadent.org.uk>
On Wed, Jan 25, 2017 at 1:43 PM, Ben Hutchings <ben@decadent.org.uk> wrote:
> On Wed, 2017-01-25 at 13:06 -0800, Andy Lutomirski wrote:
>> If an unprivileged program opens a setgid file for write and passes
>> the fd to a privileged program and the privileged program writes to
>> it, we currently fail to clear the setgid bit. Fix it by checking
>> f_cred instead of current's creds whenever a struct file is
>> involved.
> [...]
>
> What if, instead, a privileged program passes the fd to an un
> unprivileged program? It sounds like a bad idea to start with, but at
> least currently the unprivileged program is going to clear the setgid
> bit when it writes. This change would make that behaviour more
> dangerous.
Hmm. Although, if a privileged program does something like:
(sudo -u nobody echo blah) >setuid_program
presumably it wanted to make the change.
>
> Perhaps there should be a capability check on both the current
> credentials and file credentials? (I realise that we've considered
> file credential checks to be sufficient elsewhere, but those cases
> involved virtual files with special semantics, where it's clearer that
> a privileged process should not pass them to an unprivileged process.)
>
I could go either way.
What I really want to do is to write a third patch that isn't for
-stable that just removes the capable() check entirely. I'm
reasonably confident it won't break things for a silly reason: because
it's capable() and not ns_capable(), anything it would break would
also be broken in an unprivileged container, and I haven't seen any
reports of package managers or similar breaking for this reason.
--Andy
next prev parent reply other threads:[~2017-01-25 21:48 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-01-25 21:06 [PATCH 0/2] setgid hardening Andy Lutomirski
2017-01-25 21:06 ` [PATCH 1/2] fs: Check f_cred instead of current's creds in should_remove_suid() Andy Lutomirski
2017-01-25 21:43 ` Ben Hutchings
2017-01-25 21:48 ` Andy Lutomirski [this message]
2017-01-25 23:15 ` Frank Filz
2017-01-26 0:12 ` Kees Cook
2017-01-25 21:06 ` [PATCH 2/2] fs: Harden against open(..., O_CREAT, 02777) in a setgid directory Andy Lutomirski
2017-01-25 21:31 ` Ben Hutchings
2017-01-25 21:44 ` Andy Lutomirski
2017-01-25 23:17 ` Frank Filz
2017-01-25 23:50 ` Willy Tarreau
2017-01-25 23:59 ` [PATCH 0/2] setgid hardening Willy Tarreau
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