[PATCH 2/6] block: convert blk_queue_tag.refcnt from atomic_t to refcount_t
From: Elena Reshetova <elena.reshetova@intel.com>
Date: 2017-10-20 08:16:25
Also in:
linux-btrfs, linux-scsi, lkml
Subsystem:
block layer, the rest · Maintainers:
Jens Axboe, 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 blk_queue_tag.refcnt 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/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 e1a9c15..a7263e3 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 02fa42d..1fefdbb 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h@@ -26,6 +26,7 @@ #include <linux/percpu-refcount.h> #include <linux/scatterlist.h> #include <linux/blkzoned.h> +#include <linux/refcount.h> struct module; struct scsi_ioctl_command;
@@ -295,7 +296,7 @@ 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