[PATCH 03/29] drivers, char: convert vma_data.refcnt from atomic_t to refcount_t

Elena Reshetova
2017-03-06T14:20:50Z

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@intel.com>
Signed-off-by: Hans Liljestrand <ishkamiel@gmail.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: David Windsor <dwindsor@gmail.com>
---
drivers/char/mspec.c | 9 +++++----
1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/drivers/char/mspec.c b/drivers/char/mspec.c
index a9c2fa3..7b75669 100644
--- a/drivers/char/mspec.c
+++ b/drivers/char/mspec.c
@@ -43,6 +43,7 @@
#include <linux/string.h>
#include <linux/slab.h>
#include <linux/numa.h>
+#include <linux/refcount.h>
#include <asm/page.h>
#include <asm/pgtable.h>
#include <linux/atomic.h>
@@ -89,7 +90,7 @@ static int is_sn2;
* protect in fork case where multiple tasks share the vma_data.
*/
struct vma_data {
- atomic_t refcnt; /* Number of vmas sharing the data. */
+ refcount_t refcnt; /* Number of vmas sharing the data. */
spinlock_t lock; /* Serialize access to this structure. */
int count; /* Number of pages allocated. */
enum mspec_page_type type; /* Type of pages allocated. */
@@ -144,7 +145,7 @@ mspec_open(struct vm_area_struct *vma)
struct vma_data *vdata;

vdata = vma->vm_private_data;
- atomic_inc(&vdata->refcnt);
+ refcount_inc(&vdata->refcnt);
}

/*
@@ -162,7 +163,7 @@ mspec_close(struct vm_area_struct *vma)

vdata = vma->vm_private_data;

- if (!atomic_dec_and_test(&vdata->refcnt))
+ if (!refcount_dec_and_test(&vdata->refcnt))
return;

last_index = (vdata->vm_end - vdata->vm_start) >> PAGE_SHIFT;
@@ -274,7 +275,7 @@ mspec_mmap(struct file *file, struct vm_area_struct *vma,
vdata->vm_end = vma->vm_end;
vdata->type = type;
spin_lock_init(&vdata->lock);
- atomic_set(&vdata->refcnt, 1);
+ refcount_set(&vdata->refcnt, 1);
vma->vm_private_data = vdata;

vma->vm_flags |= VM_IO | VM_PFNMAP | VM_DONTEXPAND | VM_DONTDUMP;
--
2.7.4