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Message-Id: <1504095773-22895-16-git-send-email-elena.reshetova@intel.com>
Date: Wed, 30 Aug 2017 15:22:53 +0300
From: Elena Reshetova <elena.reshetova@...el.com>
To: linux-kernel@...r.kernel.org
Cc: linux-fsdevel@...r.kernel.org, peterz@...radead.org,
gregkh@...uxfoundation.org, viro@...iv.linux.org.uk, tj@...nel.org,
mingo@...hat.com, hannes@...xchg.org, lizefan@...wei.com,
acme@...nel.org, alexander.shishkin@...ux.intel.com,
eparis@...hat.com, akpm@...ux-foundation.org, arnd@...db.de,
luto@...nel.org, keescook@...omium.org, tglx@...utronix.de,
dvhart@...radead.org, ebiederm@...ssion.com,
Elena Reshetova <elena.reshetova@...el.com>
Subject: [PATCH 15/15] kcov: convert kcov.refcount to refcount_t
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@...omium.org>
Reviewed-by: David Windsor <dwindsor@...il.com>
Reviewed-by: Hans Liljestrand <ishkamiel@...il.com>
Signed-off-by: Elena Reshetova <elena.reshetova@...el.com>
---
kernel/kcov.c | 9 +++++----
1 file changed, 5 insertions(+), 4 deletions(-)
diff --git a/kernel/kcov.c b/kernel/kcov.c
index cd77199..a6c7df3 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>
/*
@@ -35,7 +36,7 @@ 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;
@@ -94,12 +95,12 @@ EXPORT_SYMBOL(__sanitizer_cov_trace_pc);
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);
}
@@ -175,7 +176,7 @@ static int kcov_open(struct inode *inode, struct file *filep)
kcov = kzalloc(sizeof(*kcov), GFP_KERNEL);
if (!kcov)
return -ENOMEM;
- 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
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