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

[Elena Reshetova]

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.reshet...@intel.com>
Signed-off-by: Hans Liljestrand <ishkam...@gmail.com>
Signed-off-by: Kees Cook <keesc...@chromium.org>
Signed-off-by: David Windsor <dwind...@gmail.com>
---
 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

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