linux-kernel - Re: [PATCH v10 1/2] fork: extend clone3() to support setting a PID

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Date:   Fri, 15 Nov 2019 11:49:10 +0100
From:   Oleg Nesterov <oleg@...hat.com>
To:     Christian Brauner <christian.brauner@...ntu.com>
Cc:     Andrei Vagin <avagin@...il.com>, Adrian Reber <areber@...hat.com>,
        Eric Biederman <ebiederm@...ssion.com>,
        Pavel Emelyanov <ovzxemul@...il.com>,
        Jann Horn <jannh@...gle.com>,
        Dmitry Safonov <0x7f454c46@...il.com>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        linux-kernel@...r.kernel.org, Mike Rapoport <rppt@...ux.ibm.com>,
        Radostin Stoyanov <rstoyanov1@...il.com>
Subject: Re: [PATCH v10 1/2] fork: extend clone3() to support setting a PID

On 11/15, Christian Brauner wrote:
>
> +static int set_tid_next(pid_t *set_tid, size_t *size, int idx)
> +{
> +	int tid = 0;
> +
> +	if (*size) {
> +		tid = set_tid[idx];
> +		if (tid < 1 || tid >= pid_max)
> +			return -EINVAL;
> +
> +		/*
> +		 * Also fail if a PID != 1 is requested and
> +		 * no PID 1 exists.
> +		 */
> +		if (tid != 1 && !tmp->child_reaper)
> +			return -EINVAL;
> +
> +		if (!ns_capable(tmp->user_ns, CAP_SYS_ADMIN))
> +			return -EPERM;
> +
> +		(*size)--;
> +	}

this needs more args, struct pid_namespace *tmp + pid_t pid_max

> +
> +	return tid;
> +}
> +
>  struct pid *alloc_pid(struct pid_namespace *ns, pid_t *set_tid,
>  		      size_t set_tid_size)
>  {
> @@ -188,20 +213,10 @@ struct pid *alloc_pid(struct pid_namespace *ns, pid_t *set_tid,
>  	for (i = ns->level; i >= 0; i--) {
>  		int tid = 0;
>  
> -		if (set_tid_size) {
> -			tid = set_tid[ns->level - i];
> -			if (tid < 1 || tid >= pid_max)
> -				return ERR_PTR(-EINVAL);
> -			/*
> -			 * Also fail if a PID != 1 is requested and
> -			 * no PID 1 exists.
> -			 */
> -			if (tid != 1 && !tmp->child_reaper)
> -				return ERR_PTR(-EINVAL);
> -			if (!ns_capable(tmp->user_ns, CAP_SYS_ADMIN))
> -				return ERR_PTR(-EPERM);
> -			set_tid_size--;
> -		}
> +		retval = set_tid_next(set_tid, &set_tid_size, ns->level - i);
> +		if (retval < 0)
> +			goto out_free;
> +		tid = retval;

Well, if we add a helper then

	static inline int check_tid(tid, max, ns)
	{
		if (tid < 1 || tid >= max)
			return ERR_PTR(-EINVAL);
		/*
		 * Also fail if a PID != 1 is requested and
		 * no PID 1 exists.
		 */
		if (tid != 1 && !ns->child_reaper)
			return ERR_PTR(-EINVAL);
		if (!ns_capable(ns->user_ns, CAP_SYS_ADMIN))
			return ERR_PTR(-EPERM);
		return 0;
	}

	... alloc_pid() ...

		if (set_tid_size) {
			tid = set_tid[ns->level - i];
			retval = check_tid(tid, pid_max, tmp);
			if (retval)
				goto out_free;
			set_tid_size--;
		}

looks more clean to me. But still ugly. IMO,

		if (set_tid_size) {
			tid = set_tid[ns->level - i];

			retval = -EINVAL;
			if (tid < 1 || tid >= pid_max)
				goto out_free;
			/*
			 * Also fail if a PID != 1 is requested and
			 * no PID 1 exists.
			 */
			if (tid != 1 && !tmp->child_reaper)
				goto out_free;
			retval = -EPERM;
			if (!ns_capable(tmp->user_ns, CAP_SYS_ADMIN))
				goto out_free;
			set_tid_size--;
		}

makes more sense.

Oleg.