[PATCH 29/29] drivers, xen: convert grant_map.users from atomic_t to refcount_t

Elena Reshetova
2017-03-06T14:21:16Z

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/xen/gntdev.c | 11 ++++++-----
1 file changed, 6 insertions(+), 5 deletions(-)

diff --git a/drivers/xen/gntdev.c b/drivers/xen/gntdev.c
index 2ef2b61..b183cb2 100644
--- a/drivers/xen/gntdev.c
+++ b/drivers/xen/gntdev.c
@@ -35,6 +35,7 @@
#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>
@@ -85,7 +86,7 @@ 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;
@@ -165,7 +166,7 @@ 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;

@@ -211,7 +212,7 @@ 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);
@@ -399,7 +400,7 @@ 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)
@@ -1003,7 +1004,7 @@ 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;

--
2.7.4

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