linux-kernel - [PATCH -mm] ipc-mqueuec-change-__do_notify-to-bypass-check_kill

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Date:   Fri, 27 Mar 2020 20:56:43 +0100
From:   Oleg Nesterov <oleg@...hat.com>
To:     "Eric W. Biederman" <ebiederm@...ssion.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Davidlohr Bueso <dave@...olabs.net>,
        Manfred Spraul <manfred@...orfullife.com>,
        Markus Elfring <elfring@...rs.sourceforge.net>,
        Yoji <yoji.fujihar.min@...il.com>, linux-kernel@...r.kernel.org
Subject: [PATCH -mm]
 ipc-mqueuec-change-__do_notify-to-bypass-check_kill_permission-fix

On 03/26, Eric W. Biederman wrote:
>
> > +			task = pid_task(info->notify_owner, PIDTYPE_PID);
>                                                             ^^^^^^^^^^^^
> Minor nit:  If we are doing the task lookup ourselves that can and
>             should be PIDTYPE_TGID.

I think this shouldn't make any difference, in particular because
do_mq_notify() does "notify_owner = task_tgid()" and we do not care
about exec.

But I agree, pid_task(PIDTYPE_TGID) looks better, thanks.


diff --git a/ipc/mqueue.c b/ipc/mqueue.c
index 63b164932ffd..9a44dcb04e13 100644
--- a/ipc/mqueue.c
+++ b/ipc/mqueue.c
@@ -801,7 +801,7 @@ static void __do_notify(struct mqueue_inode_info *info)
 			 * bypass check_kill_permission(). It is from kernel
 			 * but si_fromuser() can't know this.
 			 */
-			task = pid_task(info->notify_owner, PIDTYPE_PID);
+			task = pid_task(info->notify_owner, PIDTYPE_TGID);
 			if (task)
 				do_send_sig_info(info->notify.sigev_signo,
 						&sig_i, task, PIDTYPE_TGID);