[PATCH 5/6] block: convert bsg_device.ref_count from atomic_t to refcount_t
From: Elena Reshetova <elena.reshetova@intel.com>
Date: 2017-10-20 08:16:34
Also in:
linux-btrfs, linux-scsi, lkml
Subsystem:
block layer, bsg (block layer generic sg v4 driver), the rest · Maintainers:
Jens Axboe, FUJITA Tomonori, Linus Torvalds
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 bsg_device.ref_count is used as pure reference counter. Convert it to refcount_t and fix up the operations. Suggested-by: Kees Cook <redacted> Reviewed-by: David Windsor <redacted> Reviewed-by: Hans Liljestrand <redacted> Signed-off-by: Elena Reshetova <elena.reshetova@intel.com> --- block/bsg.c | 9 +++++---- 1 file changed, 5 insertions(+), 4 deletions(-)
diff --git a/block/bsg.c b/block/bsg.c
index ee1335c..6c98422 100644
--- a/block/bsg.c
+++ b/block/bsg.c@@ -21,6 +21,7 @@ #include <linux/idr.h> #include <linux/bsg.h> #include <linux/slab.h> +#include <linux/refcount.h> #include <scsi/scsi.h> #include <scsi/scsi_ioctl.h>
@@ -38,7 +39,7 @@ struct bsg_device { struct list_head busy_list; struct list_head done_list; struct hlist_node dev_list; - atomic_t ref_count; + refcount_t ref_count; int queued_cmds; int done_cmds; wait_queue_head_t wq_done;
@@ -710,7 +711,7 @@ static int bsg_put_device(struct bsg_device *bd) mutex_lock(&bsg_mutex); - do_free = atomic_dec_and_test(&bd->ref_count); + do_free = refcount_dec_and_test(&bd->ref_count); if (!do_free) { mutex_unlock(&bsg_mutex); goto out;
@@ -768,7 +769,7 @@ static struct bsg_device *bsg_add_device(struct inode *inode, bsg_set_block(bd, file); - atomic_set(&bd->ref_count, 1); + refcount_set(&bd->ref_count, 1); mutex_lock(&bsg_mutex); hlist_add_head(&bd->dev_list, bsg_dev_idx_hash(iminor(inode)));
@@ -788,7 +789,7 @@ static struct bsg_device *__bsg_get_device(int minor, struct request_queue *q) hlist_for_each_entry(bd, bsg_dev_idx_hash(minor), dev_list) { if (bd->queue == q) { - atomic_inc(&bd->ref_count); + refcount_inc(&bd->ref_count); goto found; } }
--
2.7.4