linux-kernel - [PATCH 2/5] fs: convert posix_acl.a_refcount from atomic_t to refcount

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Date:   Wed,  1 Mar 2017 12:42:14 +0200
From:   Elena Reshetova <elena.reshetova@...el.com>
To:     linux-kernel@...r.kernel.org
Cc:     linux-fsdevel@...r.kernel.org, peterz@...radead.org,
        gregkh@...uxfoundation.org, viro@...iv.linux.org.uk,
        jlayton@...chiereds.net, bfields@...ldses.org,
        ebiederm@...ssion.com, john.hammond@...el.com,
        Elena Reshetova <elena.reshetova@...el.com>,
        Hans Liljestrand <ishkamiel@...il.com>,
        Kees Cook <keescook@...omium.org>,
        David Windsor <dwindsor@...il.com>
Subject: [PATCH 2/5] fs: convert posix_acl.a_refcount 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>
---
 fs/f2fs/acl.c             | 2 +-
 fs/posix_acl.c            | 6 +++---
 include/linux/posix_acl.h | 7 ++++---
 3 files changed, 8 insertions(+), 7 deletions(-)

diff --git a/fs/f2fs/acl.c b/fs/f2fs/acl.c
index 8f48769..b9fc36d 100644
--- a/fs/f2fs/acl.c
+++ b/fs/f2fs/acl.c
@@ -266,7 +266,7 @@ static struct posix_acl *f2fs_acl_clone(const struct posix_acl *acl,
 				sizeof(struct posix_acl_entry);
 		clone = kmemdup(acl, size, flags);
 		if (clone)
-			atomic_set(&clone->a_refcount, 1);
+			refcount_set(&clone->a_refcount, 1);
 	}
 	return clone;
 }
diff --git a/fs/posix_acl.c b/fs/posix_acl.c
index c9d48dc..07161b9 100644
--- a/fs/posix_acl.c
+++ b/fs/posix_acl.c
@@ -42,7 +42,7 @@ struct posix_acl *get_cached_acl(struct inode *inode, int type)
 		rcu_read_lock();
 		acl = rcu_dereference(*p);
 		if (!acl || is_uncached_acl(acl) ||
-		    atomic_inc_not_zero(&acl->a_refcount))
+		    refcount_inc_not_zero(&acl->a_refcount))
 			break;
 		rcu_read_unlock();
 		cpu_relax();
@@ -163,7 +163,7 @@ EXPORT_SYMBOL(get_acl);
 void
 posix_acl_init(struct posix_acl *acl, int count)
 {
-	atomic_set(&acl->a_refcount, 1);
+	refcount_set(&acl->a_refcount, 1);
 	acl->a_count = count;
 }
 EXPORT_SYMBOL(posix_acl_init);
@@ -196,7 +196,7 @@ posix_acl_clone(const struct posix_acl *acl, gfp_t flags)
 		           sizeof(struct posix_acl_entry);
 		clone = kmemdup(acl, size, flags);
 		if (clone)
-			atomic_set(&clone->a_refcount, 1);
+			refcount_set(&clone->a_refcount, 1);
 	}
 	return clone;
 }
diff --git a/include/linux/posix_acl.h b/include/linux/posix_acl.h
index 5a9a739..e3a4fc9 100644
--- a/include/linux/posix_acl.h
+++ b/include/linux/posix_acl.h
@@ -11,6 +11,7 @@
 #include <linux/bug.h>
 #include <linux/slab.h>
 #include <linux/rcupdate.h>
+#include <linux/refcount.h>
 #include <uapi/linux/posix_acl.h>
 
 struct posix_acl_entry {
@@ -23,7 +24,7 @@ struct posix_acl_entry {
 };
 
 struct posix_acl {
-	atomic_t		a_refcount;
+	refcount_t		a_refcount;
 	struct rcu_head		a_rcu;
 	unsigned int		a_count;
 	struct posix_acl_entry	a_entries[0];
@@ -40,7 +41,7 @@ static inline struct posix_acl *
 posix_acl_dup(struct posix_acl *acl)
 {
 	if (acl)
-		atomic_inc(&acl->a_refcount);
+		refcount_inc(&acl->a_refcount);
 	return acl;
 }
 
@@ -50,7 +51,7 @@ posix_acl_dup(struct posix_acl *acl)
 static inline void
 posix_acl_release(struct posix_acl *acl)
 {
-	if (acl && atomic_dec_and_test(&acl->a_refcount))
+	if (acl && refcount_dec_and_test(&acl->a_refcount))
 		kfree_rcu(acl, a_rcu);
 }
 
-- 
2.7.4