linux-kernel - Re: [PATCH] security: protect legacy apps from insufficient privilege

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Date:	Wed, 21 May 2008 22:41:37 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	"Andrew G. Morgan" <morgan@...nel.org>
Cc:	"Serge E. Hallyn" <serue@...ibm.com>,
	lkml <linux-kernel@...r.kernel.org>,
	Linux Security Modules List 
	<linux-security-module@...r.kernel.org>
Subject: Re: [PATCH] security: protect legacy apps from insufficient
 privilege

On Wed, 21 May 2008 08:50:25 -0700 "Andrew G. Morgan" <morgan@...nel.org> wrote:

> +	CAP_FOR_EACH_U32(i) {
> +		if (i >= tocopy) {
> +			/*
> +			 * Legacy capability sets have no upper bits
> +			 */
> +			bprm->cap_post_exec_permitted.cap[i] = 0;
> +		} else {
> +			__u32 value_cpu;
> +			/*
> +			 * pP' = (X & fP) | (pI & fI)
> +			 */
> +			value_cpu = le32_to_cpu(caps->data[i].permitted);
> +			bprm->cap_post_exec_permitted.cap[i] = (
> +					current->cap_bset.cap[i] & value_cpu
> +				) | (
> +					current->cap_inheritable.cap[i] &
> +					le32_to_cpu(caps->data[i].inheritable)
> +				);
> +			if (value_cpu &
> +			    ~bprm->cap_post_exec_permitted.cap[i]) {
> +				/*
> +				 * insufficient to execute correctly
> +				 */
> +				ret = -EPERM;
> +			}
> +		}
>  	}

That makes my eyes say ow.  The 80-col thing is a pain.

With a judiciously placed `continue' we can do this:

	CAP_FOR_EACH_U32(i) {
		__u32 value_cpu;

		if (i >= tocopy) {
			/*
			 * Legacy capability sets have no upper bits
			 */
			bprm->cap_post_exec_permitted.cap[i] = 0;
			continue;
		}
		/*
		 * pP' = (X & fP) | (pI & fI)
		 */
		value_cpu = le32_to_cpu(caps->data[i].permitted);
		bprm->cap_post_exec_permitted.cap[i] =
			(current->cap_bset.cap[i] & value_cpu) |
			(current->cap_inheritable.cap[i] &
				le32_to_cpu(caps->data[i].inheritable));
		if (value_cpu & ~bprm->cap_post_exec_permitted.cap[i]) {
			/*
			 * insufficient to execute correctly
			 */
			ret = -EPERM;
		}
	}

OK?
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