[PATCH 2/5] block: convert blk_queue_tag.refcnt from atomic_t to refcount_t

Elena Reshetova
2017-04-20T11:33:21Z

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>
---
block/blk-tag.c | 8 ++++----
include/linux/blkdev.h | 3 ++-
2 files changed, 6 insertions(+), 5 deletions(-)

diff --git a/block/blk-tag.c b/block/blk-tag.c
index 07cc329..d83555e 100644
--- a/block/blk-tag.c
+++ b/block/blk-tag.c
@@ -35,7 +35,7 @@ EXPORT_SYMBOL(blk_queue_find_tag);
*/
void blk_free_tags(struct blk_queue_tag *bqt)
{
- if (atomic_dec_and_test(&bqt->refcnt)) {
+ if (refcount_dec_and_test(&bqt->refcnt)) {
BUG_ON(find_first_bit(bqt->tag_map, bqt->max_depth) <
bqt->max_depth);

@@ -130,7 +130,7 @@ static struct blk_queue_tag *__blk_queue_init_tags(struct request_queue *q,
if (init_tag_map(q, tags, depth))
goto fail;

- atomic_set(&tags->refcnt, 1);
+ refcount_set(&tags->refcnt, 1);
tags->alloc_policy = alloc_policy;
tags->next_tag = 0;
return tags;
@@ -180,7 +180,7 @@ int blk_queue_init_tags(struct request_queue *q, int depth,
queue_flag_set(QUEUE_FLAG_QUEUED, q);
return 0;
} else
- atomic_inc(&tags->refcnt);
+ refcount_inc(&tags->refcnt);

/*
* assign it, all done
@@ -225,7 +225,7 @@ int blk_queue_resize_tags(struct request_queue *q, int new_depth)
* Currently cannot replace a shared tag map with a new
* one, so error out if this is the case
*/
- if (atomic_read(&bqt->refcnt) != 1)
+ if (refcount_read(&bqt->refcnt) != 1)
return -EBUSY;

/*
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index aecca0e..95ef11c 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -25,6 +25,7 @@
#include <linux/percpu-refcount.h>
#include <linux/scatterlist.h>
#include <linux/blkzoned.h>
+#include <linux/refcount.h>

struct module;
struct scsi_ioctl_command;
@@ -288,7 +289,7 @@ struct blk_queue_tag {
unsigned long *tag_map; /* bit map of free/busy tags */
int max_depth; /* what we will send to device */
int real_max_depth; /* what the array can hold */
- atomic_t refcnt; /* map can be shared */
+ refcount_t refcnt; /* map can be shared */
int alloc_policy; /* tag allocation policy */
int next_tag; /* next tag */
};
--
2.7.4