linux-kernel - Re: [PATCH] Smack: replace capable() with ns

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Date:	Sat, 25 Jul 2015 09:59:15 -0700
From:	Casey Schaufler <casey@...aufler-ca.com>
To:	Lukasz Pawelczyk <l.pawelczyk@...sung.com>,
	Sungbae Yoo <sungbae.yoo@...sung.com>
Cc:	James Morris <james.l.morris@...cle.com>,
	"Serge E. Hallyn" <serge@...lyn.com>,
	linux-security-module@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Casey Schaufler <casey@...aufler-ca.com>
Subject: Re: [PATCH] Smack: replace capable() with ns_capable()

On 7/24/2015 4:40 AM, Lukasz Pawelczyk wrote:
> On pią, 2015-07-24 at 20:26 +0900, Sungbae Yoo wrote:
>> If current task has capabilities, Smack operations (eg. Changing own 
>> smack
>> label) should be available even inside of namespace.
>>
>> Signed-off-by: Sungbae Yoo <sungbae.yoo@...sung.com>

For the reasons Lukasz outlines below.

Nacked-by: Casey Schaufler <casey@...aufler-ca.com>

>>
>> diff --git a/security/smack/smack_access.c 
>> b/security/smack/smack_access.c
>> index 00f6b38..f6b2c35 100644
>> --- a/security/smack/smack_access.c
>> +++ b/security/smack/smack_access.c
>> @@ -639,7 +639,7 @@ int smack_privileged(int cap)
>>  	struct smack_known *skp = smk_of_current();
>>  	struct smack_onlycap *sop;
>>  
>> -	if (!capable(cap))
>> +	if (!ns_capable(current_user_ns(), cap))
>>  		return 0;
> It's not that easy.
>
> With this change Smack becomes completely insecure. You can change
> rules as an unprivileged user without any problems now.
> What you want is Smack namespace that was made to remedy exactly this
> issue (e.g. changing own labels inside a namespace).
>
>>  
>>  	rcu_read_lock();
>> diff --git a/security/smack/smack_lsm.c b/security/smack/smack_lsm.c
>> index a143328..7fdc3dd 100644
>> --- a/security/smack/smack_lsm.c
>> +++ b/security/smack/smack_lsm.c
>> @@ -403,7 +403,8 @@ static int smk_ptrace_rule_check(struct 
>> task_struct *tracer,
>>  			rc = 0;
>>  		else if (smack_ptrace_rule == 
>> SMACK_PTRACE_DRACONIAN)
>>  			rc = -EACCES;
>> -		else if (capable(CAP_SYS_PTRACE))
>> +		else if (ns_capable(__task_cred(tracer)->user_ns,
>> +				    CAP_SYS_PTRACE))
>>  			rc = 0;
>>  		else
>>  			rc = -EACCES;

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