linux-kernel - [PATCH 10/19] kernel: convert nsproxy.count from atomic_t to refcount

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Message-Id: <1487585948-6401-11-git-send-email-elena.reshetova@intel.com>
Date:   Mon, 20 Feb 2017 12:18:59 +0200
From:   Elena Reshetova <elena.reshetova@...el.com>
To:     linux-kernel@...r.kernel.org
Cc:     cgroups@...r.kernel.org, linux-audit@...hat.com,
        linux-fsdevel@...r.kernel.org, peterz@...radead.org,
        gregkh@...uxfoundation.org, viro@...iv.linux.org.uk, tj@...nel.org,
        mingo@...hat.com, hannes@...xchg.org, lizefan@...wei.com,
        acme@...nel.org, alexander.shishkin@...ux.intel.com,
        paul@...l-moore.com, eparis@...hat.com, akpm@...ux-foundation.org,
        arnd@...db.de, luto@...nel.org,
        Elena Reshetova <elena.reshetova@...el.com>,
        Hans Liljestrand <ishkamiel@...il.com>,
        Kees Cook <keescook@...omium.org>,
        David Windsor <dwindsor@...il.com>
Subject: [PATCH 10/19] kernel: convert nsproxy.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.

Signed-off-by: Elena Reshetova <elena.reshetova@...el.com>
Signed-off-by: Hans Liljestrand <ishkamiel@...il.com>
Signed-off-by: Kees Cook <keescook@...omium.org>
Signed-off-by: David Windsor <dwindsor@...il.com>
---
 include/linux/nsproxy.h | 6 +++---
 kernel/nsproxy.c        | 6 +++---
 2 files changed, 6 insertions(+), 6 deletions(-)

diff --git a/include/linux/nsproxy.h b/include/linux/nsproxy.h
index ac0d65b..f862ba8 100644
--- a/include/linux/nsproxy.h
+++ b/include/linux/nsproxy.h
@@ -28,7 +28,7 @@ struct fs_struct;
  * nsproxy is copied.
  */
 struct nsproxy {
-	atomic_t count;
+	refcount_t count;
 	struct uts_namespace *uts_ns;
 	struct ipc_namespace *ipc_ns;
 	struct mnt_namespace *mnt_ns;
@@ -74,14 +74,14 @@ int __init nsproxy_cache_init(void);
 
 static inline void put_nsproxy(struct nsproxy *ns)
 {
-	if (atomic_dec_and_test(&ns->count)) {
+	if (refcount_dec_and_test(&ns->count)) {
 		free_nsproxy(ns);
 	}
 }
 
 static inline void get_nsproxy(struct nsproxy *ns)
 {
-	atomic_inc(&ns->count);
+	refcount_inc(&ns->count);
 }
 
 #endif
diff --git a/kernel/nsproxy.c b/kernel/nsproxy.c
index 782102e..435a0f9 100644
--- a/kernel/nsproxy.c
+++ b/kernel/nsproxy.c
@@ -30,7 +30,7 @@
 static struct kmem_cache *nsproxy_cachep;
 
 struct nsproxy init_nsproxy = {
-	.count			= ATOMIC_INIT(1),
+	.count			= REFCOUNT_INIT(1),
 	.uts_ns			= &init_uts_ns,
 #if defined(CONFIG_POSIX_MQUEUE) || defined(CONFIG_SYSVIPC)
 	.ipc_ns			= &init_ipc_ns,
@@ -51,7 +51,7 @@ static inline struct nsproxy *create_nsproxy(void)
 
 	nsproxy = kmem_cache_alloc(nsproxy_cachep, GFP_KERNEL);
 	if (nsproxy)
-		atomic_set(&nsproxy->count, 1);
+		refcount_set(&nsproxy->count, 1);
 	return nsproxy;
 }
 
@@ -224,7 +224,7 @@ void switch_task_namespaces(struct task_struct *p, struct nsproxy *new)
 	p->nsproxy = new;
 	task_unlock(p);
 
-	if (ns && atomic_dec_and_test(&ns->count))
+	if (ns && refcount_dec_and_test(&ns->count))
 		free_nsproxy(ns);
 }
 
-- 
2.7.4