linux-kernel - [PATCH, RESEND] exit_notify: kill the wrong capable(CAP

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Message-ID: <20090406141602.GA17561@redhat.com>
Date:	Mon, 6 Apr 2009 16:16:02 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Chris Evans <scarybeasts@...il.com>,
	David Howells <dhowells@...hat.com>,
	Don Howard <dhoward@...hat.com>,
	Eugene Teo <eugene@...hat.com>,
	Michael Kerrisk <mtk.manpages@...glemail.com>,
	Roland McGrath <roland@...hat.com>,
	Tavis Ormandy <taviso@....lonestar.org>,
	Vitaly Mayatskikh <vmayatsk@...hat.com>,
	linux-kernel@...r.kernel.org, Serge Hallyn <serue@...ibm.com>
Subject: [PATCH, RESEND] exit_notify: kill the wrong capable(CAP_KILL) check

The CAP_KILL check in exit_notify() looks just wrong, kill it.

Whatever logic we have to reset ->exit_signal, the malicious user
can bypass it if it execs the setuid application before exiting.

Signed-off-by: Oleg Nesterov <oleg@...hat.com>
Acked-by: Serge Hallyn <serue@...ibm.com>

--- 6.30/kernel/exit.c~EXIT_CAP_KILL	2009-04-06 00:03:42.000000000 +0200
+++ 6.30/kernel/exit.c	2009-04-06 15:30:32.000000000 +0200
@@ -837,8 +837,7 @@ static void exit_notify(struct task_stru
 	 */
 	if (tsk->exit_signal != SIGCHLD && !task_detached(tsk) &&
 	    (tsk->parent_exec_id != tsk->real_parent->self_exec_id ||
-	     tsk->self_exec_id != tsk->parent_exec_id) &&
-	    !capable(CAP_KILL))
+	     tsk->self_exec_id != tsk->parent_exec_id))
 		tsk->exit_signal = SIGCHLD;
 
 	signal = tracehook_notify_death(tsk, &cookie, group_dead);

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