linux-kernel - [PATCH 1/5] fs: convert mb_cache_entry.e_refcnt from atomic_t to refcount

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Date:   Wed,  1 Mar 2017 12:42:13 +0200
From:   Elena Reshetova <elena.reshetova@...el.com>
To:     linux-kernel@...r.kernel.org
Cc:     linux-fsdevel@...r.kernel.org, peterz@...radead.org,
        gregkh@...uxfoundation.org, viro@...iv.linux.org.uk,
        jlayton@...chiereds.net, bfields@...ldses.org,
        ebiederm@...ssion.com, john.hammond@...el.com,
        Elena Reshetova <elena.reshetova@...el.com>,
        Hans Liljestrand <ishkamiel@...il.com>,
        Kees Cook <keescook@...omium.org>,
        David Windsor <dwindsor@...il.com>
Subject: [PATCH 1/5] fs: convert mb_cache_entry.e_refcnt from atomic_t to refcount_t

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@...el.com>
Signed-off-by: Hans Liljestrand <ishkamiel@...il.com>
Signed-off-by: Kees Cook <keescook@...omium.org>
Signed-off-by: David Windsor <dwindsor@...il.com>
---
 fs/mbcache.c            | 16 ++++++++--------
 include/linux/mbcache.h |  6 +++---
 2 files changed, 11 insertions(+), 11 deletions(-)

diff --git a/fs/mbcache.c b/fs/mbcache.c
index b19be429d..57a82de 100644
--- a/fs/mbcache.c
+++ b/fs/mbcache.c
@@ -89,7 +89,7 @@ int mb_cache_entry_create(struct mb_cache *cache, gfp_t mask, u32 key,
 
 	INIT_LIST_HEAD(&entry->e_list);
 	/* One ref for hash, one ref returned */
-	atomic_set(&entry->e_refcnt, 1);
+	refcount_set(&entry->e_refcnt, 1);
 	entry->e_key = key;
 	entry->e_block = block;
 	entry->e_reusable = reusable;
@@ -108,7 +108,7 @@ int mb_cache_entry_create(struct mb_cache *cache, gfp_t mask, u32 key,
 	spin_lock(&cache->c_list_lock);
 	list_add_tail(&entry->e_list, &cache->c_list);
 	/* Grab ref for LRU list */
-	atomic_inc(&entry->e_refcnt);
+	refcount_inc(&entry->e_refcnt);
 	cache->c_entry_count++;
 	spin_unlock(&cache->c_list_lock);
 
@@ -140,7 +140,7 @@ static struct mb_cache_entry *__entry_find(struct mb_cache *cache,
 		entry = hlist_bl_entry(node, struct mb_cache_entry,
 				       e_hash_list);
 		if (entry->e_key == key && entry->e_reusable) {
-			atomic_inc(&entry->e_refcnt);
+			refcount_inc(&entry->e_refcnt);
 			goto out;
 		}
 		node = node->next;
@@ -203,7 +203,7 @@ struct mb_cache_entry *mb_cache_entry_get(struct mb_cache *cache, u32 key,
 	hlist_bl_lock(head);
 	hlist_bl_for_each_entry(entry, node, head, e_hash_list) {
 		if (entry->e_key == key && entry->e_block == block) {
-			atomic_inc(&entry->e_refcnt);
+			refcount_inc(&entry->e_refcnt);
 			goto out;
 		}
 	}
@@ -239,7 +239,7 @@ void mb_cache_entry_delete_block(struct mb_cache *cache, u32 key,
 			if (!list_empty(&entry->e_list)) {
 				list_del_init(&entry->e_list);
 				cache->c_entry_count--;
-				atomic_dec(&entry->e_refcnt);
+				refcount_dec(&entry->e_refcnt);
 			}
 			spin_unlock(&cache->c_list_lock);
 			mb_cache_entry_put(cache, entry);
@@ -300,7 +300,7 @@ static unsigned long mb_cache_shrink(struct mb_cache *cache,
 		hlist_bl_lock(head);
 		if (!hlist_bl_unhashed(&entry->e_hash_list)) {
 			hlist_bl_del_init(&entry->e_hash_list);
-			atomic_dec(&entry->e_refcnt);
+			refcount_dec(&entry->e_refcnt);
 		}
 		hlist_bl_unlock(head);
 		if (mb_cache_entry_put(cache, entry))
@@ -397,11 +397,11 @@ void mb_cache_destroy(struct mb_cache *cache)
 	list_for_each_entry_safe(entry, next, &cache->c_list, e_list) {
 		if (!hlist_bl_unhashed(&entry->e_hash_list)) {
 			hlist_bl_del_init(&entry->e_hash_list);
-			atomic_dec(&entry->e_refcnt);
+			refcount_dec(&entry->e_refcnt);
 		} else
 			WARN_ON(1);
 		list_del(&entry->e_list);
-		WARN_ON(atomic_read(&entry->e_refcnt) != 1);
+		WARN_ON(refcount_read(&entry->e_refcnt) != 1);
 		mb_cache_entry_put(cache, entry);
 	}
 	kfree(cache->c_hash);
diff --git a/include/linux/mbcache.h b/include/linux/mbcache.h
index 86c9a8b..251e268 100644
--- a/include/linux/mbcache.h
+++ b/include/linux/mbcache.h
@@ -4,7 +4,7 @@
 #include <linux/hash.h>
 #include <linux/list_bl.h>
 #include <linux/list.h>
-#include <linux/atomic.h>
+#include <linux/refcount.h>
 #include <linux/fs.h>
 
 struct mb_cache;
@@ -14,7 +14,7 @@ struct mb_cache_entry {
 	struct list_head	e_list;
 	/* Hash table list - protected by hash chain bitlock */
 	struct hlist_bl_node	e_hash_list;
-	atomic_t		e_refcnt;
+	refcount_t		e_refcnt;
 	/* Key in hash - stable during lifetime of the entry */
 	u32			e_key;
 	u32			e_referenced:1;
@@ -32,7 +32,7 @@ void __mb_cache_entry_free(struct mb_cache_entry *entry);
 static inline int mb_cache_entry_put(struct mb_cache *cache,
 				     struct mb_cache_entry *entry)
 {
-	if (!atomic_dec_and_test(&entry->e_refcnt))
+	if (!refcount_dec_and_test(&entry->e_refcnt))
 		return 0;
 	__mb_cache_entry_free(entry);
 	return 1;
-- 
2.7.4