ipc: convert ipc_namespace.count from atomic_t to refcount_t

refcount_t type and corresponding API should be used instead of atomic_t
when the variable is used as a reference counter.  This allows to avoid
accidental refcounter overflows that might lead to use-after-free
situations.

Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Elena Reshetova <[email protected]>
Signed-off-by: Hans Liljestrand <[email protected]>
Signed-off-by: Kees Cook <[email protected]>
Signed-off-by: David Windsor <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Greg Kroah-Hartman <[email protected]>
Cc: "Eric W. Biederman" <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Alexey Dobriyan <[email protected]>
Cc: Serge Hallyn <[email protected]>
Cc: <[email protected]>
Cc: Davidlohr Bueso <[email protected]>
Cc: Manfred Spraul <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

Author: ereshetova

include/linux/ipc_namespace.h

@@ -7,6 +7,7 @@
 #include <linux/notifier.h>
 #include <linux/nsproxy.h>
 #include <linux/ns_common.h>
+#include <linux/refcount.h>
 
 struct user_namespace;
 
@@ -19,7 +20,7 @@ struct ipc_ids {
 };
 
 struct ipc_namespace {
-	atomic_t	count;
+	refcount_t	count;
 	struct ipc_ids	ids[3];
 
 	int		sem_ctls[4];
@@ -118,7 +119,7 @@ extern struct ipc_namespace *copy_ipcs(unsigned long flags,
 static inline struct ipc_namespace *get_ipc_ns(struct ipc_namespace *ns)
 {
 	if (ns)
-		atomic_inc(&ns->count);
+		refcount_inc(&ns->count);
 	return ns;
 }
 

ipc/msgutil.c

@@ -29,7 +29,7 @@ DEFINE_SPINLOCK(mq_lock);
  * and not CONFIG_IPC_NS.
  */
 struct ipc_namespace init_ipc_ns = {
-	.count		= ATOMIC_INIT(1),
+	.count		= REFCOUNT_INIT(1),
 	.user_ns = &init_user_ns,
 	.ns.inum = PROC_IPC_INIT_INO,
 #ifdef CONFIG_IPC_NS

ipc/namespace.c

@@ -50,7 +50,7 @@ static struct ipc_namespace *create_ipc_ns(struct user_namespace *user_ns,
 		goto fail_free;
 	ns->ns.ops = &ipcns_operations;
 
-	atomic_set(&ns->count, 1);
+	refcount_set(&ns->count, 1);
 	ns->user_ns = get_user_ns(user_ns);
 	ns->ucounts = ucounts;
 
@@ -144,7 +144,7 @@ static void free_ipc_ns(struct ipc_namespace *ns)
  */
 void put_ipc_ns(struct ipc_namespace *ns)
 {
-	if (atomic_dec_and_lock(&ns->count, &mq_lock)) {
+	if (refcount_dec_and_lock(&ns->count, &mq_lock)) {
 		mq_clear_sbinfo(ns);
 		spin_unlock(&mq_lock);
 		mq_put_mnt(ns);