f2fs: avoid overflow when large directory feathure is enabled

When large directory feathure is enable, We have one case which could cause
overflow in dir_buckets() as following:
special case: level + dir_level >= 32 and level < MAX_DIR_HASH_DEPTH / 2.

Here we define MAX_DIR_BUCKETS to limit the return value when the condition
could trigger potential overflow.

Changes from V1
 o modify description of calculation in f2fs.txt suggested by Changman Lee.

Suggested-by: Changman Lee <cm224.lee@samsung.com>
Signed-off-by: Chao Yu <chao2.yu@samsung.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

1 files changed, 2 insertions, 2 deletions

diff --git a/fs/f2fs/dir.c b/fs/f2fs/dir.c
index c3f148555c37..966acb039e3b 100644
--- a/fs/f2fs/dir.c
+++ b/fs/f2fs/dir.c
@@ -23,10 +23,10 @@ static unsigned long dir_blocks(struct inode *inode)
 
 static unsigned int dir_buckets(unsigned int level, int dir_level)
 {
-        if (level < MAX_DIR_HASH_DEPTH / 2)
+        if (level + dir_level < MAX_DIR_HASH_DEPTH / 2)
                 return 1 << (level + dir_level);
         else
-                return 1 << ((MAX_DIR_HASH_DEPTH / 2 + dir_level) - 1);
+                return MAX_DIR_BUCKETS;
 }
 
 static unsigned int bucket_blocks(unsigned int level)