linux-kernel - Re: [PATCH 4/7] allow killing tasks in your own or child userns

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <4D2BDAF4.9040908@cs.columbia.edu>
Date:	Mon, 10 Jan 2011 23:22:12 -0500
From:	Oren Laadan <orenl@...columbia.edu>
To:	Serge Hallyn <serge.hallyn@...onical.com>
CC:	Bastian Blank <bastian@...di.eu.org>,
	"Serge E. Hallyn" <serge@...lyn.com>,
	containers@...ts.linux-foundation.org,
	kernel list <linux-kernel@...r.kernel.org>,
	LSM <linux-security-module@...r.kernel.org>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Kees Cook <kees.cook@...onical.com>,
	Alexey Dobriyan <adobriyan@...il.com>,
	Michael Kerrisk <mtk.manpages@...il.com>
Subject: Re: [PATCH 4/7] allow killing tasks in your own or child userns



On 01/10/2011 05:51 PM, Serge Hallyn wrote:
> Quoting Bastian Blank (bastian@...di.eu.org):
>> On Mon, Jan 10, 2011 at 09:13:34PM +0000, Serge E. Hallyn wrote:
>>> +	const struct cred *cred = current_cred();
>>> +	const struct cred *tcred = __task_cred(t);
>>> +
>>> +	if (cred->user->user_ns != tcred->user->user_ns) {
>>> +		/* userids are not equivalent - either you have the
>>> +		   capability to the target user ns or you don't */
>>> +		if (ns_capable(tcred->user->user_ns, CAP_KILL))
>>> +			return 1;
>>> +		return 0;
>>> +	}
>>> +
>>> +	/* same user namespace - usual credentials checks apply */
>>> +	if ((cred->euid ^ tcred->suid) &&
>>> +	    (cred->euid ^ tcred->uid) &&
>>> +	    (cred->uid  ^ tcred->suid) &&
>>> +	    (cred->uid  ^ tcred->uid) &&
>>> +	    !ns_capable(tcred->user->user_ns, CAP_KILL))
>>> +		return 0;
>>> +
>>> +	return 1;
>>
>> Isn't that equal to this?
>>
>> 	if (ns_capable(tcred->user->user_ns, CAP_KILL))
>> 		return 1;
>>
>> 	if (cred->user->user_ns == tcred->user->user_ns &&
>> 	    (cred->euid == tcred->suid ||
>> 	     cred->euid == tcred->uid ||
>> 	     cred->uid == tcred->suid ||
>> 	     cred->uid == tcred->uid))
>> 		return 1;
>>
>> 	return 0;
>>
>> I would consider this much easier to read.
> 
> Unfortunately, it's actually not equivalent.  when capable()
> returns success, then it sets the current->flags |= PF_SUPERPRIV.
> If permission is granted based on userids and the capability
> isn't needed, then we don't want to needlessly set PF_SUPERPRIV.

A bit off-topic: does this means that c/r needs to save and 
restore this process flag ?
> 
> That's why I'm going to such lengths to call capable() as a last
> resort.

IMHO, worth a one line comment in the code ...

Oren.
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/