linux-kernel - [PATCH 2/3] ipc: sysvsem: force unshare(CLONE_SYSVSEM) when CLONE

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Message-ID: <20080416164338.GA24563@sergelap.austin.ibm.com>
Date:	Wed, 16 Apr 2008 11:43:38 -0500
From:	"Serge E. Hallyn" <serue@...ibm.com>
To:	lkml <linux-kernel@...r.kernel.org>, Andrew Morton <akpm@...l.org>
Cc:	Pavel Emelyanov <xemul@...nvz.org>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Manfred Spraul <manfred@...orfullife.com>,
	Michael Kerrisk <mtk.manpages@...glemail.com>,
	Nadia Derbey <Nadia.Derbey@...l.net>
Subject: [PATCH 2/3] ipc: sysvsem: force unshare(CLONE_SYSVSEM) when
	CLONE_NEWIPC

sys_unshare(CLONE_NEWIPC) doesn't handle the undo lists properly, this can
cause a kernel memory corruption. CLONE_NEWIPC must detach from the existing
undo lists.
Fix, part 2: perform an implicit CLONE_SYSVSEM in CLONE_NEWIPC.
CLONE_NEWIPC creates a new IPC namespace, the task cannot access the
existing semaphore arrays after the unshare syscall. Thus the task
can/must detach from the existing undo list entries, too.

This fixes the kernel corruption, because it makes it impossible that
undo records from two different namespaces are in sysvsem.undo_list.

Signed-off-by: Manfred Spraul <manfred@...orfullife.com>
Signed-off-by: Serge E. Hallyn <serue@...ibm.com>
---
 kernel/fork.c |    7 ++++++-
 1 files changed, 6 insertions(+), 1 deletions(-)

diff --git a/kernel/fork.c b/kernel/fork.c
index 56fa5ae..4c28232 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -1705,7 +1705,12 @@ asmlinkage long sys_unshare(unsigned long unshare_flags)
 				CLONE_NEWNET))
 		goto bad_unshare_out;
 
-	if (unshare_flags & CLONE_SYSVSEM)
+	/*
+	 * CLONE_NEWIPC must also detach from the undolist: after switching
+	 * to a new ipc namespace, the semaphore arrays from the old
+	 * namespace are unreachable.
+	 */
+	if (unshare_flags & (CLONE_NEWIPC|CLONE_SYSVSEM))
 		do_sysvsem = 1;
 	if ((err = unshare_thread(unshare_flags)))
 		goto bad_unshare_out;
-- 
1.5.1.1.GIT

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