[PATCH 2/3] ipc: sysvsem: force unshare(CLONE_SYSVSEM) when CLONE_NEWIPC

["Serge E. Hallyn" <serue@us.ibm.com>]

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@colorfullife.com>
Signed-off-by: Serge E. Hallyn <serue@us.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