[PATCH 2/2] fix sys_unshare()+SEM_UNDO: perform an implicit CLONE_SYSVSEM in CLONE_NEWIPC

[Manfred Spraul <manfred@colorfullife.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.

I'm not sure who's the right maintainer, Andrew, could you merge it?

Signed-off-by: Manfred Spraul <manfred@colorfullife.com>
---
 kernel/fork.c |    6 +++++-
 1 files changed, 5 insertions(+), 1 deletions(-)

diff --git a/kernel/fork.c b/kernel/fork.c
index 7f242b0..6f956a7 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -1735,9 +1735,13 @@ asmlinkage long sys_unshare(unsigned long unshare_flags)
 		goto bad_unshare_cleanup_semundo;
 
 	if (new_fs ||  new_mm || new_fd || new_ulist || new_nsproxy) {
-		if (unshare_flags & CLONE_SYSVSEM) {
+		if (unshare_flags & (CLONE_NEWIPC|CLONE_SYSVSEM)) {
 			/*
 			 * CLONE_SYSVSEM is equivalent to sys_exit().
+			 *
+			 * CLONE_NEWIPC must also detach from the undolist: after switching
+			 * to a new ipc namespace, the semaphore arrays from the old
+			 * namespace are unreachable.
 			 */
 			exit_sem(current);
 		}
-- 
1.5.4.1