linux-kernel - Re: [PATCH] signal: don't silently convert SI

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Date:   Mon, 8 Apr 2019 15:13:16 +0200
From:   Oleg Nesterov <oleg@...hat.com>
To:     Jann Horn <jannh@...gle.com>
Cc:     Christian Brauner <christian@...uner.io>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        Arnd Bergmann <arnd@...db.de>,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] signal: don't silently convert SI_USER signals to
 non-current pidfd

On 03/30, Jann Horn wrote:
>
> --- a/kernel/signal.c
> +++ b/kernel/signal.c
> @@ -3605,16 +3605,11 @@ SYSCALL_DEFINE4(pidfd_send_signal, int, pidfd, int, sig,
>  		if (unlikely(sig != kinfo.si_signo))
>  			goto err;
>
> +		/* Only allow sending arbitrary signals to yourself. */
> +		ret = -EPERM;
>  		if ((task_pid(current) != pid) &&
> -		    (kinfo.si_code >= 0 || kinfo.si_code == SI_TKILL)) {
> -			/* Only allow sending arbitrary signals to yourself. */
> -			ret = -EPERM;
> -			if (kinfo.si_code != SI_USER)
> -				goto err;
> -
> -			/* Turn this into a regular kill signal. */
> -			prepare_kill_siginfo(sig, &kinfo);
> -		}
> +		    (kinfo.si_code >= 0 || kinfo.si_code == SI_TKILL))
> +			goto err;

ACK.


but perhaps it should always fail, even if task_pid(current) == pid.

sys_rt_sigqueueinfo() allows to send any siginfo to yourself, but this is only needed
for checkpoint/restart.

Oleg.