[PATCH 11/19] kernel: convert cgroup_namespace.count from atomic_t to refcount_t

[Elena Reshetova]

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.

Signed-off-by: Elena Reshetova <elena.reshet...@intel.com>
Signed-off-by: Hans Liljestrand <ishkam...@gmail.com>
Signed-off-by: Kees Cook <keesc...@chromium.org>
Signed-off-by: David Windsor <dwind...@gmail.com>
---
 include/linux/cgroup.h    | 7 ++++---
 kernel/cgroup/cgroup.c    | 2 +-
 kernel/cgroup/namespace.c | 2 +-
 3 files changed, 6 insertions(+), 5 deletions(-)

diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index f6b43fb..4412979 100644
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -22,6 +22,7 @@
 #include <linux/ns_common.h>
 #include <linux/nsproxy.h>
 #include <linux/user_namespace.h>
+#include <linux/refcount.h>
 
 #include <linux/cgroup-defs.h>
 
@@ -640,7 +641,7 @@ static inline void cgroup_sk_free(struct sock_cgroup_data 
*skcd) {}
 #endif /* CONFIG_CGROUP_DATA */
 
 struct cgroup_namespace {
-       atomic_t                count;
+       refcount_t              count;
        struct ns_common        ns;
        struct user_namespace   *user_ns;
        struct ucounts          *ucounts;
@@ -675,12 +676,12 @@ copy_cgroup_ns(unsigned long flags, struct user_namespace 
*user_ns,
 static inline void get_cgroup_ns(struct cgroup_namespace *ns)
 {
        if (ns)
-               atomic_inc(&ns->count);
+               refcount_inc(&ns->count);
 }
 
 static inline void put_cgroup_ns(struct cgroup_namespace *ns)
 {
-       if (ns && atomic_dec_and_test(&ns->count))
+       if (ns && refcount_dec_and_test(&ns->count))
                free_cgroup_ns(ns);
 }
 
diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c
index ffcb310..5b94c79 100644
--- a/kernel/cgroup/cgroup.c
+++ b/kernel/cgroup/cgroup.c
@@ -188,7 +188,7 @@ static u16 have_canfork_callback __read_mostly;
 
 /* cgroup namespace for init task */
 struct cgroup_namespace init_cgroup_ns = {
-       .count          = { .counter = 2, },
+       .count          = REFCOUNT_INIT(2),
        .user_ns        = &init_user_ns,
        .ns.ops         = &cgroupns_operations,
        .ns.inum        = PROC_CGROUP_INIT_INO,
diff --git a/kernel/cgroup/namespace.c b/kernel/cgroup/namespace.c
index cff7ea6..86e9bbe 100644
--- a/kernel/cgroup/namespace.c
+++ b/kernel/cgroup/namespace.c
@@ -31,7 +31,7 @@ static struct cgroup_namespace *alloc_cgroup_ns(void)
                kfree(new_ns);
                return ERR_PTR(ret);
        }
-       atomic_set(&new_ns->count, 1);
+       refcount_set(&new_ns->count, 1);
        new_ns->ns.ops = &cgroupns_operations;
        return new_ns;
 }
-- 
2.7.4