On 10/20/2017 12:57 AM, Elena Reshetova wrote:
atomic_t variables are currently used to implement reference
counters with the following properties:
- counter is initialized to 1 using atomic_set()
- a resource is freed upon counter reaching zero
- once counter reaches zero, its further
increments aren't allowed
- counter schema uses basic atomic operations
(set, inc, inc_not_zero, dec_and_test, etc.)
Such atomic variables should be converted to a newly provided
refcount_t type and API that prevents accidental counter overflows
and underflows. This is important since overflows and underflows
can lead to use-after-free situation and be exploitable.
The variable mdesc_handle.refcnt is used as pure reference counter.
Convert it to refcount_t and fix up the operations.
Suggested-by: Kees Cook <keesc...@chromium.org>
Reviewed-by: David Windsor <dwind...@gmail.com>
Reviewed-by: Hans Liljestrand <ishkam...@gmail.com>
Signed-off-by: Elena Reshetova <elena.reshet...@intel.com>
Acked-by: Shannon Nelson <shannon.nel...@oracle.com>
---
arch/sparc/kernel/mdesc.c | 17 +++++++++--------
1 file changed, 9 insertions(+), 8 deletions(-)
diff --git a/arch/sparc/kernel/mdesc.c b/arch/sparc/kernel/mdesc.c
index fa466ce..821a724 100644
--- a/arch/sparc/kernel/mdesc.c
+++ b/arch/sparc/kernel/mdesc.c
@@ -12,6 +12,7 @@
#include <linux/miscdevice.h>
#include <linux/bootmem.h>
#include <linux/export.h>
+#include <linux/refcount.h>
#include <asm/cpudata.h>
#include <asm/hypervisor.h>
@@ -70,7 +71,7 @@ struct mdesc_handle {
struct list_head list;
struct mdesc_mem_ops *mops;
void *self_base;
- atomic_t refcnt;
+ refcount_t refcnt;
unsigned int handle_size;
struct mdesc_hdr mdesc;
};
@@ -152,7 +153,7 @@ static void mdesc_handle_init(struct mdesc_handle *hp,
memset(hp, 0, handle_size);
INIT_LIST_HEAD(&hp->list);
hp->self_base = base;
- atomic_set(&hp->refcnt, 1);
+ refcount_set(&hp->refcnt, 1);
hp->handle_size = handle_size;
}
@@ -182,7 +183,7 @@ static void __init mdesc_memblock_free(struct mdesc_handle *hp)
unsigned int alloc_size;
unsigned long start;
- BUG_ON(atomic_read(&hp->refcnt) != 0);
+ BUG_ON(refcount_read(&hp->refcnt) != 0);
BUG_ON(!list_empty(&hp->list));
alloc_size = PAGE_ALIGN(hp->handle_size);
@@ -220,7 +221,7 @@ static struct mdesc_handle *mdesc_kmalloc(unsigned int
mdesc_size)
static void mdesc_kfree(struct mdesc_handle *hp)
{
- BUG_ON(atomic_read(&hp->refcnt) != 0);
+ BUG_ON(refcount_read(&hp->refcnt) != 0);
BUG_ON(!list_empty(&hp->list));
kfree(hp->self_base);
@@ -259,7 +260,7 @@ struct mdesc_handle *mdesc_grab(void)
spin_lock_irqsave(&mdesc_lock, flags);
hp = cur_mdesc;
if (hp)
- atomic_inc(&hp->refcnt);
+ refcount_inc(&hp->refcnt);
spin_unlock_irqrestore(&mdesc_lock, flags);
return hp;
@@ -271,7 +272,7 @@ void mdesc_release(struct mdesc_handle *hp)
unsigned long flags;
spin_lock_irqsave(&mdesc_lock, flags);
- if (atomic_dec_and_test(&hp->refcnt)) {
+ if (refcount_dec_and_test(&hp->refcnt)) {
list_del_init(&hp->list);
hp->mops->free(hp);
}
@@ -513,7 +514,7 @@ void mdesc_update(void)
if (status != HV_EOK || real_len > len) {
printk(KERN_ERR "MD: mdesc reread fails with %lu\n",
status);
- atomic_dec(&hp->refcnt);
+ refcount_dec(&hp->refcnt);
mdesc_free(hp);
goto out;
}
@@ -526,7 +527,7 @@ void mdesc_update(void)
mdesc_notify_clients(orig_hp, hp);
spin_lock_irqsave(&mdesc_lock, flags);
- if (atomic_dec_and_test(&orig_hp->refcnt))
+ if (refcount_dec_and_test(&orig_hp->refcnt))
mdesc_free(orig_hp);
else
list_add(&orig_hp->list, &mdesc_zombie_list);
