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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: Changman Lee <cm224.lee@samsung.com>
Signed-off-by: Chao Yu <chao2.yu@samsung.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
This commit is contained in:
Chao Yu 2014-05-28 08:56:09 +08:00 committed by Jaegeuk Kim
parent d631abdac9
commit bfec07d0f8
3 changed files with 9 additions and 6 deletions
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8
Documentation/filesystems/f2fs.txt
View File

@ -461,11 +461,11 @@ The number of blocks and buckets are determined by,
# of blocks in level #n = |
`- 4, Otherwise
,- 2^ (n + dir_level),
| if n < MAX_DIR_HASH_DEPTH / 2,
,- 2^(n + dir_level),
| if n + dir_level < MAX_DIR_HASH_DEPTH / 2,
# of buckets in level #n = |
`- 2^((MAX_DIR_HASH_DEPTH / 2 + dir_level) - 1),
Otherwise
`- 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
name is calculated. Then, F2FS scans the hash table in level #0 to find the

4
fs/f2fs/dir.c
View File

@ -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)

3
include/linux/f2fs_fs.h
View File

@ -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)