[PATCH 2/5] fs: convert posix_acl.a_refcount 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>
---
 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