linux-kernel - Re: [PATCH] signal: Fix the error return of kill -1

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Message-ID: <20230816210634.GA10130@redhat.com>
Date:   Wed, 16 Aug 2023 23:06:34 +0200
From:   Oleg Nesterov <oleg@...hat.com>
To:     "Eric W. Biederman" <ebiederm@...ssion.com>
Cc:     David Laight <David.Laight@...LAB.COM>,
        Petr Skocik <pskocik@...il.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" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] signal: Fix the error return of kill -1

On 08/16, Eric W. Biederman wrote:
>
> Oleg Nesterov <oleg@...hat.com> writes:
>
> > On 08/15, David Laight wrote:
> >>
> >> or maybe even:
> >> 	} else {
> >> 		struct task_struct * p;
> >> 		int err;
> >> 		ret = -ESRCH;
> >>
> >> 		for_each_process(p) {
> >> 			if (task_pid_vnr(p) > 1 &&
> >> 					!same_thread_group(p, current)) {
> >> 				err = group_send_sig_info(sig, info, p,
> >> 							  PIDTYPE_MAX);
> >> 				if (ret)
> >> 					ret = err;
> >
> > Hmm, indeed ;)
> >
> > and "err" can be declared inside the loop.
>
> We can't remove the success case, from my posted patch.
>
> A signal is considered as successfully delivered if at least
> one process receives it.

Yes.

Initially ret = -ESRCH.

Once group_send_sig_info() succeeds at least once (returns zero)
ret becomes 0.

After that

	if (ret)
		ret = err;

has no effect.

So if a signal is successfully delivered at least once the code
above returns zero.

Oleg.