linux-kernel - Re: [PATCH] signal: Avoid corrupting si_pid and si_uid in do_notify

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Date:   Tue, 21 Apr 2020 11:04:27 +0200
From:   Oleg Nesterov <oleg@...hat.com>
To:     "Eric W. Biederman" <ebiederm@...ssion.com>
Cc:     linux-kernel@...r.kernel.org,
        Christof Meerwald <cmeerw@...erw.org>,
        Linux Containers <containers@...ts.linux-foundation.org>
Subject: Re: [PATCH] signal: Avoid corrupting si_pid and si_uid in
 do_notify_parent

On 04/20, Eric W. Biederman wrote:
>
> The immediate problem is as Christof noticed that "pid_alive(current) == false".

this is slightly offtopic, but we can probably remove this "pid_alive" check,
pid_nr_ns() checks pid != NULL anyway.

> Inspecting the code it appears this problem has existed since the pid
> namespace support started handling this case

Agreed...

> @@ -1993,8 +1993,12 @@ bool do_notify_parent(struct task_struct *tsk, int sig)
>  		if (psig->action[SIGCHLD-1].sa.sa_handler == SIG_IGN)
>  			sig = 0;
>  	}
> +	/*
> +	 * Bypass send_signal as the si_pid and si_uid values have
> +	 * been generated in the parent's namespaces.
> +	 */
>  	if (valid_signal(sig) && sig)
> -		__group_send_sig_info(sig, &info, tsk->parent);
> +		__send_signal(sig, &info, tsk->parent, PIDTYPE_TGID, false);

Acked-by: Oleg Nesterov <oleg@...hat.com>