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

[Elena Reshetova <elena.reshetova@xxxxxxxxx>]

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@xxxxxxxxx>
Signed-off-by: Hans Liljestrand <ishkamiel@xxxxxxxxx>
Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
Signed-off-by: David Windsor <dwindsor@xxxxxxxxx>
---
 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


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