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Commit bfec07d0 authored by Chao Yu's avatar Chao Yu Committed by Jaegeuk Kim
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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: default avatarChangman Lee <cm224.lee@samsung.com>
Signed-off-by: default avatarChao Yu <chao2.yu@samsung.com>
Signed-off-by: default avatarJaegeuk Kim <jaegeuk@kernel.org>
parent d631abda

Documentation/filesystems/f2fs.txt

+4 −4
Original line number Diff line number Diff line
@@ -462,9 +462,9 @@ The number of blocks and buckets are determined by, 
                            `- 4, Otherwise



                             ,- 2^(n + dir_level),

			     |            if n < MAX_DIR_HASH_DEPTH / 2,

			     |        if n + dir_level < MAX_DIR_HASH_DEPTH / 2,

  # of buckets in level #n = |

                             `- 2^((MAX_DIR_HASH_DEPTH / 2 + dir_level) - 1),

                             `- 2^((MAX_DIR_HASH_DEPTH / 2) - 1),

			              Otherwise



When F2FS finds a file name in a directory, at first a hash value of the file

fs/f2fs/dir.c

+2 −2
Original line number Diff line number Diff line
@@ -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)

include/linux/f2fs_fs.h

+3 −0
Original line number Diff line number Diff line
@@ -394,6 +394,9 @@ typedef __le32 f2fs_hash_t; 
/* MAX level for dir lookup */

#define MAX_DIR_HASH_DEPTH	63



/* MAX buckets in one level of dir */

#define MAX_DIR_BUCKETS		(1 << ((MAX_DIR_HASH_DEPTH / 2) - 1))



#define SIZE_OF_DIR_ENTRY	11	/* by byte */

#define SIZE_OF_DENTRY_BITMAP	((NR_DENTRY_IN_BLOCK + BITS_PER_BYTE - 1) / \

					BITS_PER_BYTE)