[PATCH 3/3] ipc: sysvsem: refuse clone(CLONE_SYSVSEM|CLONE_NEWIPC)

[Serge E. Hallyn]

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.

Signed-off-by: Serge E. Hallyn <serue@xxxxxxxxxx>
---
 kernel/nsproxy.c |   12 ++++++++++++
 1 files changed, 12 insertions(+), 0 deletions(-)

diff --git a/kernel/nsproxy.c b/kernel/nsproxy.c
index f5d332c..468ade3 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);
-- 
1.5.1.1.GIT

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