[PATCH 05/17] fs, btrfs: convert btrfs_caching_control.count from atomic_t to refcount_t

From: Elena Reshetova
Date: Fri Mar 03 2017 - 04:04:48 EST


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@xxxxxxxxx>
Signed-off-by: Hans Liljestrand <ishkamiel@xxxxxxxxx>
Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
Signed-off-by: David Windsor <dwindsor@xxxxxxxxx>
---
fs/btrfs/ctree.h | 3 ++-
fs/btrfs/extent-tree.c | 12 ++++++------
2 files changed, 8 insertions(+), 7 deletions(-)

diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
index 00e3518..557af39 100644
--- a/fs/btrfs/ctree.h
+++ b/fs/btrfs/ctree.h
@@ -38,6 +38,7 @@
#include <linux/security.h>
#include <linux/sizes.h>
#include <linux/dynamic_debug.h>
+#include <linux/refcount.h>
#include "extent_io.h"
#include "extent_map.h"
#include "async-thread.h"
@@ -517,7 +518,7 @@ struct btrfs_caching_control {
struct btrfs_work work;
struct btrfs_block_group_cache *block_group;
u64 progress;
- atomic_t count;
+ refcount_t count;
};

/* Once caching_thread() finds this much free space, it will wake up waiters. */
diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index 63ba295..796001b 100644
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -315,14 +315,14 @@ get_caching_control(struct btrfs_block_group_cache *cache)
}

ctl = cache->caching_ctl;
- atomic_inc(&ctl->count);
+ refcount_inc(&ctl->count);
spin_unlock(&cache->lock);
return ctl;
}

static void put_caching_control(struct btrfs_caching_control *ctl)
{
- if (atomic_dec_and_test(&ctl->count))
+ if (refcount_dec_and_test(&ctl->count))
kfree(ctl);
}

@@ -598,7 +598,7 @@ static int cache_block_group(struct btrfs_block_group_cache *cache,
init_waitqueue_head(&caching_ctl->wait);
caching_ctl->block_group = cache;
caching_ctl->progress = cache->key.objectid;
- atomic_set(&caching_ctl->count, 1);
+ refcount_set(&caching_ctl->count, 1);
btrfs_init_work(&caching_ctl->work, btrfs_cache_helper,
caching_thread, NULL, NULL);

@@ -619,7 +619,7 @@ static int cache_block_group(struct btrfs_block_group_cache *cache,
struct btrfs_caching_control *ctl;

ctl = cache->caching_ctl;
- atomic_inc(&ctl->count);
+ refcount_inc(&ctl->count);
prepare_to_wait(&ctl->wait, &wait, TASK_UNINTERRUPTIBLE);
spin_unlock(&cache->lock);

@@ -706,7 +706,7 @@ static int cache_block_group(struct btrfs_block_group_cache *cache,
}

down_write(&fs_info->commit_root_sem);
- atomic_inc(&caching_ctl->count);
+ refcount_inc(&caching_ctl->count);
list_add_tail(&caching_ctl->list, &fs_info->caching_block_groups);
up_write(&fs_info->commit_root_sem);

@@ -10415,7 +10415,7 @@ int btrfs_remove_block_group(struct btrfs_trans_handle *trans,
&fs_info->caching_block_groups, list)
if (ctl->block_group == block_group) {
caching_ctl = ctl;
- atomic_inc(&caching_ctl->count);
+ refcount_inc(&caching_ctl->count);
break;
}
}
--
2.7.4