[PATCH 1/5] block: convert bio.__bi_cnt from atomic_t to refcount_t

Elena Reshetova
2017-04-20T11:27:53Z

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/bio.c | 6 +++---
fs/btrfs/volumes.c | 2 +-
include/linux/bio.h | 4 ++--
include/linux/blk_types.h | 3 ++-
4 files changed, 8 insertions(+), 7 deletions(-)

diff --git a/block/bio.c b/block/bio.c
index 5eec5e0..3dffc17 100644
--- a/block/bio.c
+++ b/block/bio.c
@@ -275,7 +275,7 @@ void bio_init(struct bio *bio, struct bio_vec *table,
{
memset(bio, 0, sizeof(*bio));
atomic_set(&bio->__bi_remaining, 1);
- atomic_set(&bio->__bi_cnt, 1);
+ refcount_set(&bio->__bi_cnt, 1);

bio->bi_io_vec = table;
bio->bi_max_vecs = max_vecs;
@@ -543,12 +543,12 @@ void bio_put(struct bio *bio)
if (!bio_flagged(bio, BIO_REFFED))
bio_free(bio);
else {
- BIO_BUG_ON(!atomic_read(&bio->__bi_cnt));
+ BIO_BUG_ON(!refcount_read(&bio->__bi_cnt));

/*
* last put frees it
*/
- if (atomic_dec_and_test(&bio->__bi_cnt))
+ if (refcount_dec_and_test(&bio->__bi_cnt))
bio_free(bio);
}
}
diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index 13e55d1..ff1fe9d 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -441,7 +441,7 @@ static noinline void run_scheduled_bios(struct btrfs_device *device)
waitqueue_active(&fs_info->async_submit_wait))
wake_up(&fs_info->async_submit_wait);

- BUG_ON(atomic_read(&cur->__bi_cnt) == 0);
+ BUG_ON(refcount_read(&cur->__bi_cnt) == 0);

/*
* if we're doing the sync list, record that our
diff --git a/include/linux/bio.h b/include/linux/bio.h
index 8e52119..44ac678 100644
--- a/include/linux/bio.h
+++ b/include/linux/bio.h
@@ -234,7 +234,7 @@ static inline void bio_get(struct bio *bio)
{
bio->bi_flags |= (1 << BIO_REFFED);
smp_mb__before_atomic();
- atomic_inc(&bio->__bi_cnt);
+ refcount_inc(&bio->__bi_cnt);
}

static inline void bio_cnt_set(struct bio *bio, unsigned int count)
@@ -243,7 +243,7 @@ static inline void bio_cnt_set(struct bio *bio, unsigned int count)
bio->bi_flags |= (1 << BIO_REFFED);
smp_mb__before_atomic();
}
- atomic_set(&bio->__bi_cnt, count);
+ refcount_set(&bio->__bi_cnt, count);
}

static inline bool bio_flagged(struct bio *bio, unsigned int bit)
diff --git a/include/linux/blk_types.h b/include/linux/blk_types.h
index d703acb..c41407f 100644
--- a/include/linux/blk_types.h
+++ b/include/linux/blk_types.h
@@ -7,6 +7,7 @@

#include <linux/types.h>
#include <linux/bvec.h>
+#include <linux/refcount.h>

struct bio_set;
struct bio;
@@ -73,7 +74,7 @@ struct bio {

unsigned short bi_max_vecs; /* max bvl_vecs we can hold */

- atomic_t __bi_cnt; /* pin count */
+ refcount_t __bi_cnt; /* pin count */

struct bio_vec *bi_io_vec; /* the actual vec list */

--
2.7.4