ext4: fix underflow in ext4_max_bitmap_size()

hulk inclusion
category: bugfix
bugzilla: 186216, https://gitee.com/openeuler/kernel/issues/I4PW7R
CVE: NA

--------------------------------

The same to commit 1c2d1421 ("ext2: Fix underflow in ext2_max_size()")
in ext2 filesystem, ext4 driver has the same issue with 64K block size
and ^huge_file, fix this issue the same as ext2. This patch also revert
commit 75ca6ad4 ("ext4: fix loff_t overflow in ext4_max_bitmap_size()")
because it's no longer needed.
Signed-off-by: NZhang Yi <yi.zhang@huawei.com>
Signed-off-by: NBaokun Li <libaokun1@huawei.com>
Reviewed-by: NYang Erkun <yangerkun@huawei.com>
Signed-off-by: NZheng Zengkai <zhengzengkai@huawei.com>

fs/ext4/super.c

@@ -3220,8 +3220,9 @@ static loff_t ext4_max_size(int blkbits, int has_huge_files)
  */
 static loff_t ext4_max_bitmap_size(int bits, int has_huge_files)
 {
-	unsigned long long upper_limit, res = EXT4_NDIR_BLOCKS;
+	loff_t upper_limit, res = EXT4_NDIR_BLOCKS;
 	int meta_blocks;
+	unsigned int ppb = 1 << (bits - 2);
 
 	/*
 	 * This is calculated to be the largest file size for a dense, block
@@ -3253,27 +3254,42 @@ static loff_t ext4_max_bitmap_size(int bits, int has_huge_files)
 
 	}
 
-	/* indirect blocks */
-	meta_blocks = 1;
-	/* double indirect blocks */
-	meta_blocks += 1 + (1LL << (bits-2));
-	/* tripple indirect blocks */
-	meta_blocks += 1 + (1LL << (bits-2)) + (1LL << (2*(bits-2)));
-
-	upper_limit -= meta_blocks;
-	upper_limit <<= bits;
-
+	/* Compute how many blocks we can address by block tree */
 	res += 1LL << (bits-2);
 	res += 1LL << (2*(bits-2));
 	res += 1LL << (3*(bits-2));
+	/* Compute how many metadata blocks are needed */
+	meta_blocks = 1;
+	meta_blocks += 1 + ppb;
+	meta_blocks += 1 + ppb + ppb * ppb;
+	/* Does block tree limit file size? */
+	if (res + meta_blocks <= upper_limit)
+		goto check_lfs;
+
+	res = upper_limit;
+	/* How many metadata blocks are needed for addressing upper_limit? */
+	upper_limit -= EXT4_NDIR_BLOCKS;
+	/* indirect blocks */
+	meta_blocks = 1;
+	upper_limit -= ppb;
+	/* double indirect blocks */
+	if (upper_limit < ppb * ppb) {
+		meta_blocks += 1 + DIV_ROUND_UP(upper_limit, ppb);
+		res -= meta_blocks;
+		goto check_lfs;
+	}
+	meta_blocks += 1 + ppb;
+	upper_limit -= ppb * ppb;
+	/* tripple indirect blocks for the rest */
+	meta_blocks += 1 + DIV_ROUND_UP(upper_limit, ppb) +
+		DIV_ROUND_UP(upper_limit, ppb*ppb);
+	res -= meta_blocks;
+check_lfs:
 	res <<= bits;
-	if (res > upper_limit)
-		res = upper_limit;
-
 	if (res > MAX_LFS_FILESIZE)
 		res = MAX_LFS_FILESIZE;
 
-	return (loff_t)res;
+	return res;
 }
 
 static ext4_fsblk_t descriptor_loc(struct super_block *sb,