Re: [PATCH v2 2/2] pidfd: change pidfd_send_signal() to respect PIDFD_THREAD

On Wed, Feb 14, 2024 at 01:36:56PM +0100, Oleg Nesterov wrote:

On 02/10, Oleg Nesterov wrote:

quoted

On 02/10, Christian Brauner wrote:

quoted

+	if (type == PIDFD_SIGNAL_PROCESS_GROUP)
+		ret = kill_pgrp_info(sig, &kinfo, pid);

I guess you meant

	if (type == PIDTYPE_PGID)

other than that,

Reviewed-by: Oleg Nesterov <oleg@redhat.com>

Yes, but there is another thing I hadn't thought of...

sys_pidfd_send_signal() does

	/* Only allow sending arbitrary signals to yourself. */
	ret = -EPERM;
	if ((task_pid(current) != pid) &&
	    (kinfo.si_code >= 0 || kinfo.si_code == SI_TKILL))
		goto err;

and I am not sure that task_pid(current) == pid should allow
the "arbitrary signals" if PIDFD_SIGNAL_PROCESS_GROUP.

Perhaps

	/* Only allow sending arbitrary signals to yourself. */
	ret = -EPERM;
	if ((task_pid(current) != pid || type == PIDTYPE_PGID) &&
	    (kinfo.si_code >= 0 || kinfo.si_code == SI_TKILL)
		goto err;

Honestly, we should probably just do:

if (kinfo->si_code != SI_USER)
        goto err

and be done with it. If we get regressions reports about this then it's
easy to fix that up. But I find that unlikely. So why not try to get
away with something much simpler. What do you think?