linux-kernel - [PATCH] check_unshare_flags: kill the bogus CLONE

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Message-ID: <20100321184801.GA29085@redhat.com>
Date:	Sun, 21 Mar 2010 19:48:01 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Janak Desai <janak@...ibm.com>, Roland McGrath <roland@...hat.com>,
	linux-kernel@...r.kernel.org
Subject: [PATCH] check_unshare_flags: kill the bogus
	CLONE_SIGHAND/sig->count check

check_unshare_flags(CLONE_SIGHAND) adds CLONE_THREAD to *flags_ptr if the
task is multithreaded to ensure unshare_thread() will fail.

Not only this is a bit strange way to return the error, this is absolutely
meaningless. If signal->count > 1 then sighand->count must be also > 1,
and unshare_sighand() will fail anyway.

In fact, all CLONE_THREAD/SIGHAND/VM checks inside sys_unshare() do not
look right. Fortunately this code doesn't really work anyway.

Signed-off-by: Oleg Nesterov <oleg@...hat.com>
---

 kernel/fork.c |    8 --------
 1 file changed, 8 deletions(-)

--- 34-rc1/kernel/fork.c~UNSHARE_DONT_USE_SIG_COUNT	2010-03-21 18:37:31.000000000 +0100
+++ 34-rc1/kernel/fork.c	2010-03-21 19:08:06.000000000 +0100
@@ -1519,14 +1519,6 @@ static void check_unshare_flags(unsigned
 		*flags_ptr |= CLONE_SIGHAND;
 
 	/*
-	 * If unsharing signal handlers and the task was created
-	 * using CLONE_THREAD, then must unshare the thread
-	 */
-	if ((*flags_ptr & CLONE_SIGHAND) &&
-	    (atomic_read(&current->signal->count) > 1))
-		*flags_ptr |= CLONE_THREAD;
-
-	/*
 	 * If unsharing namespace, must also unshare filesystem information.
 	 */
 	if (*flags_ptr & CLONE_NEWNS)

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