linux-kernel - Re: [PATCH 2/4] pid: add pidctl()

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Date:   Mon, 25 Mar 2019 17:20:54 +0000
From:   Mika Penttilä <mika.penttila@...tfour.com>
To:     Christian Brauner <christian@...uner.io>,
        "jannh@...gle.com" <jannh@...gle.com>,
        "khlebnikov@...dex-team.ru" <khlebnikov@...dex-team.ru>,
        "luto@...nel.org" <luto@...nel.org>,
        "dhowells@...hat.com" <dhowells@...hat.com>,
        "serge@...lyn.com" <serge@...lyn.com>,
        "ebiederm@...ssion.com" <ebiederm@...ssion.com>,
        "linux-api@...r.kernel.org" <linux-api@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
CC:     "arnd@...db.de" <arnd@...db.de>,
        "keescook@...omium.org" <keescook@...omium.org>,
        "adobriyan@...il.com" <adobriyan@...il.com>,
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        "joel@...lfernandes.org" <joel@...lfernandes.org>,
        "dancol@...gle.com" <dancol@...gle.com>
Subject: Re: [PATCH 2/4] pid: add pidctl()

Hi!


> +SYSCALL_DEFINE5(pidctl, unsigned int, cmd, pid_t, pid, int, source, int, target,
> +		unsigned int, flags)
> +{
> +	struct pid_namespace *source_ns = NULL, *target_ns = NULL;
> +	struct pid *struct_pid;
> +	pid_t result;
> +
> +	switch (cmd) {
> +	case PIDCMD_QUERY_PIDNS:
> +		if (pid != 0)
> +			return -EINVAL;
> +		pid = 1;
> +		/* fall through */
> +	case PIDCMD_QUERY_PID:
> +		if (flags != 0)
> +			return -EINVAL;
> +		break;
> +	case PIDCMD_GET_PIDFD:
> +		if (flags & ~PIDCTL_CLOEXEC)
> +			return -EINVAL;
> +		break;
> +	default:
> +		return -EOPNOTSUPP;
> +	}
> +
> +	source_ns = get_pid_ns_by_fd(source);
> +	result = PTR_ERR(source_ns);
> +	if (IS_ERR(source_ns))
> +		goto err_source;
> +
> +	target_ns = get_pid_ns_by_fd(target);
> +	result = PTR_ERR(target_ns);
> +	if (IS_ERR(target_ns))
> +		goto err_target;
> +
> +	if (cmd == PIDCMD_QUERY_PIDNS) {
> +		result = pidns_related(source_ns, target_ns);
> +	} else {
> +		rcu_read_lock();
> +		struct_pid = find_pid_ns(pid, source_ns);
> +		result = struct_pid ? pid_nr_ns(struct_pid, target_ns) : -ESRCH;

Should you do get_pid(struct_pid) here to keep it alive till 
pidfd_create_fd() ?

> +		rcu_read_unlock();
> +
> +		if (cmd == PIDCMD_GET_PIDFD) {
> +			int cloexec = (flags & PIDCTL_CLOEXEC) ? O_CLOEXEC : 0;
> +			if (result > 0)
> +				result = pidfd_create_fd(struct_pid, cloexec);
> +			else if (result == 0)
> +				result = -ENOENT;
> +		}
> +	}
> +
> +	if (target)
> +		put_pid_ns(target_ns);
> +err_target:
> +	if (source)
> +		put_pid_ns(source_ns);
> +err_source:
> +	return result;
> +}
> +
>  void __init pid_idr_init(void)
>  {
>  	/* Verify no one has done anything silly: */
> diff --git a/kernel/pid_namespace.c b/kernel/pid_namespace.c
> index aa6e72fb7c08..1c863fb3d55a 100644
> --- a/kernel/pid_namespace.c
> +++ b/kernel/pid_namespace.c
> @@ -429,6 +429,31 @@ static struct ns_common *pidns_get_parent(struct ns_common *ns)
>  	return &get_pid_ns(pid_ns)->ns;
>  }
>  
> +/**
> + * pidnscmp - Determine if @ancestor is ancestor of @descendant
> + * @ancestor:   pidns suspected to be the ancestor of @descendant
> + * @descendant: pidns suspected to be the descendant of @ancestor
> + *
> + * Returns -1 if @ancestor is not an ancestor of @descendant,
> + * 0 if @ancestor is the same pidns as @descendant, 1 if @ancestor
> + * is an ancestor of @descendant.
> + */
> +int pidnscmp(struct pid_namespace *ancestor, struct pid_namespace *descendant)
> +{
> +	if (ancestor == descendant)
> +		return 0;
> +
> +	for (;;) {
> +		if (!descendant)
> +			return -1;
> +		if (descendant == ancestor)
> +			break;
> +		descendant = descendant->parent;
> +	}
> +
> +	return 1;
> +}
> +
>  static struct user_namespace *pidns_owner(struct ns_common *ns)
>  {
>  	return to_pid_ns(ns)->user_ns;