ipc: sysvsem: refuse clone(CLONE_SYSVSEM|CLONE_NEWIPC)

CLONE_NEWIPC|CLONE_SYSVSEM interaction isn't handled properly.  This can cause
a kernel memory corruption.  CLONE_NEWIPC must detach from the existing undo
lists.

Fix, part 3: refuse clone(CLONE_SYSVSEM|CLONE_NEWIPC).

With unshare, specifying CLONE_SYSVSEM means unshare the sysvsem.  So it seems
reasonable that CLONE_NEWIPC without CLONE_SYSVSEM would just imply
CLONE_SYSVSEM.

However with clone, specifying CLONE_SYSVSEM means *share* the sysvsem.  So
calling clone(CLONE_SYSVSEM|CLONE_NEWIPC) is explicitly asking for something
we can't allow.  So return -EINVAL in that case.

[akpm@linux-foundation.org: cleanups]
Signed-off-by: Serge E. Hallyn <serue@us.ibm.com>
Cc: Manfred Spraul <manfred@colorfullife.com>
Acked-by: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Pavel Emelyanov <xemul@openvz.org>
Cc: Michael Kerrisk <mtk.manpages@googlemail.com>
Cc: Pierre Peiffer <peifferp@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 12 insertions, 0 deletions

diff --git a/kernel/nsproxy.c b/kernel/nsproxy.c
index f5d332cf8c6..adc785146a1 100644
--- a/kernel/nsproxy.c
+++ b/kernel/nsproxy.c
@@ -139,6 +139,18 @@ int copy_namespaces(unsigned long flags, struct task_struct *tsk)
                 goto out;
         }
 
+        /*
+         * CLONE_NEWIPC must detach from the undolist: after switching
+         * to a new ipc namespace, the semaphore arrays from the old
+         * namespace are unreachable.  In clone parlance, CLONE_SYSVSEM
+         * means share undolist with parent, so we must forbid using
+         * it along with CLONE_NEWIPC.
+         */
+        if ((flags & CLONE_NEWIPC) && (flags & CLONE_SYSVSEM)) {
+                err = -EINVAL;
+                goto out;
+        }
+
         new_ns = create_new_namespaces(flags, tsk, tsk->fs);
         if (IS_ERR(new_ns)) {
                 err = PTR_ERR(new_ns);