linux-kernel - Re: [PATCH 11/13] AppArmor: LSM interface, and security module initialization

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Date:	Thu, 15 Jul 2010 12:27:57 -0500
From:	"Serge E. Hallyn" <serge@...lyn.com>
To:	John Johansen <john.johansen@...onical.com>
Cc:	linux-kernel@...r.kernel.org, linux-security-module@...r.kernel.org
Subject: Re: [PATCH 11/13] AppArmor: LSM interface, and security module
 initialization

Quoting John Johansen (john.johansen@...onical.com):
> AppArmor hooks to interface with the LSM, module parameters and module
> initialization.
> 
> Signed-off-by: John Johansen <john.johansen@...onical.com>

Thanks, John - looks good overall.  Comments:

...

> +static int apparmor_ptrace_access_check(struct task_struct *child,
> +					unsigned int mode)
> +{
> +	int rc;
> +
> +	rc = cap_ptrace_access_check(child, mode);
> +	if (rc)
> +		return rc;
> +
> +	return aa_ptrace(current, child, mode);
> +}
> +
> +static int apparmor_ptrace_traceme(struct task_struct *parent)
> +{

Just curious - why aren't you calling cap_ptrace_traceme() first here?

> +	return aa_ptrace(parent, current, PTRACE_MODE_ATTACH);
> +}
> +
> +/* Derived from security/commoncap.c:cap_capget */
> +static int apparmor_capget(struct task_struct *target, kernel_cap_t *effective,
> +			   kernel_cap_t *inheritable, kernel_cap_t *permitted)
> +{
> +	struct aa_profile *profile;
> +	const struct cred *cred;
> +
> +	rcu_read_lock();
> +	cred = __task_cred(target);
> +	profile = aa_cred_profile(cred);
> +
> +	*effective = cred->cap_effective;
> +	*inheritable = cred->cap_inheritable;
> +	*permitted = cred->cap_permitted;
> +
> +	if (!unconfined(profile))
> +		*effective = cap_intersect(*effective, profile->caps.allow);

Should you mask permitted too?  Otherwise you might confuse a userspace
lib which assumes it's caller previously culled pE, and that it can
nwo refill it from pP.

> +	rcu_read_unlock();
> +
> +	return 0;
> +}
> +
> +static int apparmor_capable(struct task_struct *task, const struct cred *cred,
> +			    int cap, int audit)
> +{
> +	struct aa_profile *profile;
> +	/* cap_capable returns 0 on success, else -EPERM */
> +	int error = cap_capable(task, cred, cap, audit);

jinkeys, it might be just me, but i'd have spend 2 mins less looking
at this if you'd done

	if (error)
		return error;

here, simplifying the condition below.

> +
> +	profile = aa_cred_profile(cred);
> +	if (!error  && !unconfined(profile))
> +		error = aa_capable(task, profile, cap, audit);
> +
> +	return error;
> +}

-serge
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