[PATCH] coda: Convert from atomic_t to refcount_t on coda_vm_ops->refcnt

[Xiyu Yang]

refcount_t type and corresponding API can protect refcounters from
accidental underflow and overflow and further use-after-free situations.

Signed-off-by: Xiyu Yang <xiyuyang19@xxxxxxxxxxxx>
Signed-off-by: Xin Tan <tanxin.ctf@xxxxxxxxx>
---
 fs/coda/file.c | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/fs/coda/file.c b/fs/coda/file.c
index ef5ca22bfb3e..66fb420f4e77 100644
--- a/fs/coda/file.c
+++ b/fs/coda/file.c
@@ -8,6 +8,7 @@
  * to the Coda project. Contact Peter Braam <coda@xxxxxxxxxx>.
  */
 
+#include <linux/refcount.h>
 #include <linux/types.h>
 #include <linux/kernel.h>
 #include <linux/time.h>
@@ -28,7 +29,7 @@
 #include "coda_int.h"
 
 struct coda_vm_ops {
-	atomic_t refcnt;
+	refcount_t refcnt;
 	struct file *coda_file;
 	const struct vm_operations_struct *host_vm_ops;
 	struct vm_operations_struct vm_ops;
@@ -98,7 +99,7 @@ coda_vm_open(struct vm_area_struct *vma)
 	struct coda_vm_ops *cvm_ops =
 		container_of(vma->vm_ops, struct coda_vm_ops, vm_ops);
 
-	atomic_inc(&cvm_ops->refcnt);
+	refcount_inc(&cvm_ops->refcnt);
 
 	if (cvm_ops->host_vm_ops && cvm_ops->host_vm_ops->open)
 		cvm_ops->host_vm_ops->open(vma);
@@ -113,7 +114,7 @@ coda_vm_close(struct vm_area_struct *vma)
 	if (cvm_ops->host_vm_ops && cvm_ops->host_vm_ops->close)
 		cvm_ops->host_vm_ops->close(vma);
 
-	if (atomic_dec_and_test(&cvm_ops->refcnt)) {
+	if (refcount_dec_and_test(&cvm_ops->refcnt)) {
 		vma->vm_ops = cvm_ops->host_vm_ops;
 		fput(cvm_ops->coda_file);
 		kfree(cvm_ops);
@@ -189,7 +190,7 @@ coda_file_mmap(struct file *coda_file, struct vm_area_struct *vma)
 		cvm_ops->vm_ops.open = coda_vm_open;
 		cvm_ops->vm_ops.close = coda_vm_close;
 		cvm_ops->coda_file = coda_file;
-		atomic_set(&cvm_ops->refcnt, 1);
+		refcount_set(&cvm_ops->refcnt, 1);
 
 		vma->vm_ops = &cvm_ops->vm_ops;
 	}
-- 
2.7.4