lkml.org 
[lkml]   [2017]   [Oct]   [20]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
From
Subject[PATCH 14/15] kcov: convert kcov.refcount to refcount_t
Date
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 kcov.refcount is used as pure reference counter.
Convert it to refcount_t and fix up the operations.

Suggested-by: Kees Cook <keescook@chromium.org>
Reviewed-by: David Windsor <dwindsor@gmail.com>
Reviewed-by: Hans Liljestrand <ishkamiel@gmail.com>
Signed-off-by: Elena Reshetova <elena.reshetova@intel.com>
---
kernel/kcov.c | 9 +++++----
1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/kernel/kcov.c b/kernel/kcov.c
index 461c55e..03c174c 100644
--- a/kernel/kcov.c
+++ b/kernel/kcov.c
@@ -19,6 +19,7 @@
#include <linux/debugfs.h>
#include <linux/uaccess.h>
#include <linux/kcov.h>
+#include <linux/refcount.h>
#include <asm/setup.h>

/* Number of 64-bit words written per one comparison: */
@@ -43,7 +44,7 @@ struct kcov {
* - opened file descriptor
* - task with enabled coverage (we can't unwire it from another task)
*/
- atomic_t refcount;
+ refcount_t refcount;
/* The lock protects mode, size, area and t. */
spinlock_t lock;
enum kcov_mode mode;
@@ -227,12 +228,12 @@ EXPORT_SYMBOL(__sanitizer_cov_trace_switch);

static void kcov_get(struct kcov *kcov)
{
- atomic_inc(&kcov->refcount);
+ refcount_inc(&kcov->refcount);
}

static void kcov_put(struct kcov *kcov)
{
- if (atomic_dec_and_test(&kcov->refcount)) {
+ if (refcount_dec_and_test(&kcov->refcount)) {
vfree(kcov->area);
kfree(kcov);
}
@@ -310,7 +311,7 @@ static int kcov_open(struct inode *inode, struct file *filep)
if (!kcov)
return -ENOMEM;
kcov->mode = KCOV_MODE_DISABLED;
- atomic_set(&kcov->refcount, 1);
+ refcount_set(&kcov->refcount, 1);
spin_lock_init(&kcov->lock);
filep->private_data = kcov;
return nonseekable_open(inode, filep);
--
2.7.4
\
 
 \ /
  Last update: 2017-10-22 17:38    [W:2.006 / U:0.012 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site