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

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Date:	Fri, 24 Jul 2015 13:40:32 +0200
From:	Lukasz Pawelczyk <l.pawelczyk@...sung.com>
To:	Sungbae Yoo <sungbae.yoo@...sung.com>,
	Casey Schaufler <casey@...aufler-ca.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
Subject: Re: [PATCH] Smack: replace capable() with ns_capable()

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>
> 
> 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;
-- 
Lukasz Pawelczyk
Samsung R&D Institute Poland
Samsung Electronics



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