Re: [PATCH v3 06/11] rlimits: do security check under task_lock

[Andrew Morton <akpm@linux-foundation.org>]

On Mon, 10 May 2010 20:00:46 +0200
Jiri Slaby <jslaby@suse.cz> wrote:

> Do security_task_setrlimit under task_lock. Other tasks may
> change limits under our hands while we are checking limits
> inside the function. From now on, they can't.
>
> ...
>
> --- a/kernel/sys.c
> +++ b/kernel/sys.c
> @@ -1277,7 +1277,7 @@ int do_setrlimit(struct task_struct *tsk, unsigned int resource,
>  		struct rlimit *new_rlim)
>  {
>  	struct rlimit *old_rlim;
> -	int retval;
> +	int retval = 0;
>  
>  	if (resource >= RLIM_NLIMITS)
>  		return -EINVAL;
> @@ -1293,10 +1293,6 @@ int do_setrlimit(struct task_struct *tsk, unsigned int resource,
>  		goto out;
>  	}
>  
> -	retval = security_task_setrlimit(tsk, resource, new_rlim);
> -	if (retval)
> -		goto out;
> -
>  	if (resource == RLIMIT_CPU && new_rlim->rlim_cur == 0) {
>  		/*
>  		 * The caller is asking for an immediate RLIMIT_CPU
> @@ -1309,11 +1305,13 @@ int do_setrlimit(struct task_struct *tsk, unsigned int resource,
>  
>  	old_rlim = tsk->signal->rlim + resource;
>  	task_lock(tsk->group_leader);
> -	if ((new_rlim->rlim_max <= old_rlim->rlim_max) ||
> -				capable(CAP_SYS_RESOURCE))
> -		*old_rlim = *new_rlim;
> -	else
> +	if ((new_rlim->rlim_max > old_rlim->rlim_max) &&
> +				!capable(CAP_SYS_RESOURCE))
>  		retval = -EPERM;
> +	if (!retval)
> +		retval = security_task_setrlimit(tsk, resource, new_rlim);
> +	if (!retval)
> +		*old_rlim = *new_rlim;
>  	task_unlock(tsk->group_leader);
>  
>  	if (retval || resource != RLIMIT_CPU)

Yikes, so the locking around all that selinux code becomes even more
brutal.  How much rope are you tying around the selinux developers'
hands here?