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From: Bryan Donlan <bdonlan@gmail.com>
Date: Tue, 29 Dec 2009 15:43:52 -0500
Message-ID: <3e8340490912291243q7ba43fd9v266835ebbda9315b@mail.gmail.com>
Subject: Re: RFC: disablenetwork facility. (v4)
To: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Benny Amorsen <benny+usenet@amorsen.dk>,
       "Serge E. Hallyn" <serue@us.ibm.com>,
       Michael Stone <michael@laptop.org>, linux-kernel@vger.kernel.org,
       netdev@vger.kernel.org, linux-security-module@vger.kernel.org,
       Andi Kleen <andi@firstfloor.org>, David Lang <david@lang.hm>,
       Oliver Hartkopp <socketcan@hartkopp.net>,
       Alan Cox <alan@lxorguk.ukuu.org.uk>,
       Herbert Xu <herbert@gondor.apana.org.au>,
       Valdis Kletnieks <Valdis.Kletnieks@vt.edu>,
       Evgeniy Polyakov <zbr@ioremap.net>,
       "C. Scott Ananian" <cscott@cscott.net>,
       James Morris <jmorris@namei.org>, Bernie Innocenti <bernie@codewiz.org>,
       Mark Seaborn <mrs@mythic-beasts.com>,
       Randy Dunlap <randy.dunlap@oracle.com>,
       =?ISO-8859-1?Q?Am=E9rico_Wang?= <xiyou.wangcong@gmail.com>,
       Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>,
       Samir Bellabes <sam@synack.fr>,
       Casey Schaufler <casey@schaufler-ca.com>, Pavel Machek <pavel@ucw.cz>,
       Al Viro <viro@zeniv.linux.org.uk>
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On Tue, Dec 29, 2009 at 3:40 PM, Eric W. Biederman
<ebiederm@xmission.com> wrote:
> Benny Amorsen <benny+usenet@amorsen.dk> writes:
>
>> Bryan Donlan <bdonlan@gmail.com> writes:
>>
>>> I, for one, think it would be best to handle it exactly like the
>>> nosuid mount option - that is, pretend the file doesn't have any
>>> setuid bits set. There's no reason to deny execution; if the process
>>> would otherwise be able to execute it, it can also copy the file to
>>> make a non-suid version and execute that instead.
>>
>> Execute != read. The executable file may contain secrets which must not
>> be available to the user running the setuid program. If you fail the
>> setuid, the user will be able to ptrace() and then the secret is
>> revealed.
>>
>> It's amazing how many security holes appear from what seems like a very
>> simple request.
>
> Do we have a security hole in nosuid mount option?

Looks like it:
$ /tmp/m/sudo
sudo: must be setuid root
$ ls -l /tmp/m/sudo
-rwsr-x--x 1 root root 123448 2009-06-22 12:14 /tmp/m/sudo
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