linux-kernel - Re: [PATCH 1/1] Fix kill(-1,s) returning 0 on 0 kills

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Message-ID: <20221123112002.GC32207@redhat.com>
Date:   Wed, 23 Nov 2022 12:20:03 +0100
From:   Oleg Nesterov <oleg@...hat.com>
To:     Petr Skocik <pskocik@...il.com>
Cc:     "Eric W. Biederman" <ebiederm@...ssion.com>,
        Kees Cook <keescook@...omium.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Marco Elver <elver@...gle.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/1] Fix kill(-1,s) returning 0 on 0 kills

On 11/23, Oleg Nesterov wrote:
>
> On 11/22, Petr Skocik wrote:
> >
> > --- a/kernel/signal.c
> > +++ b/kernel/signal.c
> > @@ -1600,20 +1600,18 @@ static int kill_something_info(int sig, struct kernel_siginfo *info, pid_t pid)
> >  		ret = __kill_pgrp_info(sig, info,
> >  				pid ? find_vpid(-pid) : task_pgrp(current));
> >  	} else {
> > -		int retval = 0, count = 0;
> >  		struct task_struct * p;
> >
> > +		ret = -ESRCH;
> >  		for_each_process(p) {
> >  			if (task_pid_vnr(p) > 1 &&
> >  					!same_thread_group(p, current)) {
> >  				int err = group_send_sig_info(sig, info, p,
> >  							      PIDTYPE_MAX);
> > -				++count;
> >  				if (err != -EPERM)
> > -					retval = err;
> > +					ret = err; /*either all 0 or all -EINVAL*/
>
> The patch looks good to me, and it also simplifies the code.
>
> But I fail to understand the /*either all 0 or all -EINVAL*/ comment above..

OTOH... I think we do not really care, but there is another problem with
or without your patch. Suppose that group_send_sig_info() returns -EAGAIN,
then succeeds. So perhaps something like

		struct task_struct *p;
		int esrch = -ESRCH;

		ret = 0;
		for_each_process(p) {
			if (task_pid_vnr(p) > 1 &&
					!same_thread_group(p, current)) {
				int err = group_send_sig_info(sig, info, p,
							      PIDTYPE_MAX);
				if (err == 0)
					esrch = 0;
				else if (err != -EPERM)
					ret = err;
			}
		}
		ret = ret ?: esrch;

if we really want to make this code "100% correct". But again, I am not sure
this makes sense.

Oleg.