linux-kernel - Re: [RFC][PATCH v2] Unprivileged: Disable raising of privileges

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Message-ID: <m1vdfotclm.fsf@fess.ebiederm.org>
Date:	Wed, 30 Dec 2009 12:45:41 -0800
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	"Serge E. Hallyn" <serue@...ibm.com>
Cc:	Bryan Donlan <bdonlan@...il.com>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Benny Amorsen <benny+usenet@...rsen.dk>,
	Michael Stone <michael@...top.org>,
	linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
	linux-security-module@...r.kernel.org,
	Andi Kleen <andi@...stfloor.org>, David Lang <david@...g.hm>,
	Oliver Hartkopp <socketcan@...tkopp.net>,
	Herbert Xu <herbert@...dor.apana.org.au>,
	Valdis Kletnieks <Valdis.Kletnieks@...edu>,
	Evgeniy Polyakov <zbr@...emap.net>,
	"C. Scott Ananian" <cscott@...ott.net>,
	James Morris <jmorris@...ei.org>,
	Bernie Innocenti <bernie@...ewiz.org>,
	Mark Seaborn <mrs@...hic-beasts.com>,
	Randy Dunlap <randy.dunlap@...cle.com>,
	Américo Wang <xiyou.wangcong@...il.com>,
	Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>,
	Samir Bellabes <sam@...ack.fr>,
	Casey Schaufler <casey@...aufler-ca.com>,
	Pavel Machek <pavel@....cz>, Al Viro <viro@...iv.linux.org.uk>
Subject: Re: [RFC][PATCH v2] Unprivileged: Disable raising of privileges

"Serge E. Hallyn" <serue@...ibm.com> writes:

>> @@ -869,6 +869,18 @@ int cap_task_prctl(int option, unsigned long arg2, unsigned long arg3,
>>  			new->securebits &= ~issecure_mask(SECURE_KEEP_CAPS);
>>  		goto changed;
>> 
>> +	case PR_SET_NOSUID:
>> +	{
>> +		const struct cred *cred = current->cred;
>> +		error = -EINVAL;
>
> Should this be -EPERM?  not sure...

I intended -EINVAL to say it is simply a set of initial conditions
that are not supported today.  But could be supported if someone
does the audit, and found there are no security issues.

>> +		/* Perform the capabilities checks */
>> +		if (!cap_isclear(cred->cap_permitted) ||
>> +		    !cap_isclear(cred->cap_effective))
>
> No need to check cap_effective, as no bits can be there which are not
> in cap_permitted.
>
> To be honest, I don't think there is much reason to not have this
> check done in the main sys_prctl(0 - capabilities themselves are not
> optional in the kernel, while cap_task_prctl() is.  So you are setting
> us up to have cases where say an apparmor user can call this with uid
> 0 and/or active capabilities.

Sounds fine to me.  I had noticed all of the capabilities checks were
off in their own file, so I had tried to maintain that.  But you are
right we can't remove capabilities so splitting the code like this only
obfuscates it.

>> @@ -2147,7 +2147,7 @@ static int selinux_bprm_set_creds(struct linux_binprm *bprm)
>>  	COMMON_AUDIT_DATA_INIT(&ad, FS);
>>  	ad.u.fs.path = bprm->file->f_path;
>> 
>> -	if (bprm->file->f_path.mnt->mnt_flags & MNT_NOSUID)
>> +	if (bprm->nosid)
>
> typo - nosuid?

Yep.

Eric
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