linux-kernel - Re: [PATCH v4 9/9] devcg: propagate local changes down the hierarchy

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Date:	Thu, 31 Jan 2013 04:38:39 +0000
From:	"Serge E. Hallyn" <serge@...lyn.com>
To:	aris@...hat.com
Cc:	linux-kernel@...r.kernel.org, cgroups@...r.kernel.org,
	Tejun Heo <tj@...nel.org>,
	Serge Hallyn <serge.hallyn@...onical.com>
Subject: Re: [PATCH v4 9/9] devcg: propagate local changes down the
 hierarchy

Quoting aris@...hat.com (aris@...hat.com):
...
> New exceptions allowing additional access to devices won't be propagated, but
> it'll be possible to add an exception to access all of part of the newly
> allowed device(s).

Is that intended to apply only to only in the DEFAULT_DENY case?  If so
that should be made clear.  If not,

...

> @@ -515,11 +673,13 @@ 	memset(&ex, 0, sizeof(ex));
>  							 &parent->exceptions);
>  			devcgroup->behavior = DEVCG_DEFAULT_ALLOW;
>  			devcgroup->local.behavior = DEVCG_DEFAULT_ALLOW;
> +			rc = propagate_behavior(devcgroup);
>  			break;
>  		case DEVCG_DENY:
>  			dev_exception_clean_all(devcgroup);
>  			devcgroup->behavior = DEVCG_DEFAULT_DENY;
>  			devcgroup->local.behavior = DEVCG_DEFAULT_DENY;
> +			rc = propagate_behavior(devcgroup);
>  			break;
>  		default:
>  			rc = -EINVAL;
> @@ -610,9 +770,14 @@ 		case '\0':
>  		 */
>  		if (devcgroup->behavior == DEVCG_DEFAULT_ALLOW) {
>  			dev_exception_rm(devcgroup, &ex);
> -			return 0;
> +			rc = propagate_exception(devcgroup);

Let's say the default in both parent A and child B is ALLOW, and both
have a blacklist entry for "b 8:* rwm".  Now I

	echo "b 8:* rwm" > A/devices.allow

removing the blacklist entry.  Here you are propagating that to the
child B, which I would argue is actually propagating a new allow to
a child.  Which you said you wouldn't do.

> +			return rc;
>  		}
> -		return dev_exception_add(devcgroup, &ex);
> +		rc = dev_exception_add(devcgroup, &ex);
> +		if (!rc)
> +			/* if a local behavior wasn't explicitely choosen, pick it */
> +			devcgroup->local.behavior = devcgroup->behavior;
> +		break;
>  	case DEVCG_DENY:
>  		/*
>  		 * If the default policy is to deny by default, try to remove
> @@ -621,13 +786,22 @@ 			return 0;
>  		 */
>  		if (devcgroup->behavior == DEVCG_DEFAULT_DENY) {
>  			dev_exception_rm(devcgroup, &ex);
> -			return 0;
> +			rc = propagate_exception(devcgroup);
> +			return rc;
>  		}
> -		return dev_exception_add(devcgroup, &ex);
> +		rc = dev_exception_add(devcgroup, &ex);
> +		if (rc)
> +			return rc;
> +		/* we only propagate new restrictions */
> +		rc = propagate_exception(devcgroup);
> +		if (!rc)
> +			/* if a local behavior wasn't explicitely choosen, pick it */
> +			devcgroup->local.behavior = devcgroup->behavior;
> +		break;

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