drivers, xen: convert grant_map.users 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@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>
Signed-off-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>

1 files changed, 6 insertions, 5 deletions

diff --git a/drivers/xen/gntdev.c b/drivers/xen/gntdev.c
index c77a0751a311..f3bf8f4e2d6c 100644
--- a/drivers/xen/gntdev.c
+++ b/drivers/xen/gntdev.c
@@ -36,6 +36,7 @@
 #include <linux/spinlock.h>
 #include <linux/slab.h>
 #include <linux/highmem.h>
+#include <linux/refcount.h>
 
 #include <xen/xen.h>
 #include <xen/grant_table.h>
@@ -86,7 +87,7 @@ struct grant_map {
         int index;
         int count;
         int flags;
-        atomic_t users;
+        refcount_t users;
         struct unmap_notify notify;
         struct ioctl_gntdev_grant_ref *grants;
         struct gnttab_map_grant_ref   *map_ops;
@@ -166,7 +167,7 @@ static struct grant_map *gntdev_alloc_map(struct gntdev_priv *priv, int count)
 
         add->index = 0;
         add->count = count;
-        atomic_set(&add->users, 1);
+        refcount_set(&add->users, 1);
 
         return add;
 
@@ -212,7 +213,7 @@ static void gntdev_put_map(struct gntdev_priv *priv, struct grant_map *map)
         if (!map)
                 return;
 
-        if (!atomic_dec_and_test(&map->users))
+        if (!refcount_dec_and_test(&map->users))
                 return;
 
         atomic_sub(map->count, &pages_mapped);
@@ -400,7 +401,7 @@ static void gntdev_vma_open(struct vm_area_struct *vma)
         struct grant_map *map = vma->vm_private_data;
 
         pr_debug("gntdev_vma_open %p\n", vma);
-        atomic_inc(&map->users);
+        refcount_inc(&map->users);
 }
 
 static void gntdev_vma_close(struct vm_area_struct *vma)
@@ -1004,7 +1005,7 @@ static int gntdev_mmap(struct file *flip, struct vm_area_struct *vma)
                 goto unlock_out;
         }
 
-        atomic_inc(&map->users);
+        refcount_inc(&map->users);
 
         vma->vm_ops = &gntdev_vmops;