On Tue 01-03-22 19:17:04, Zhang Yi wrote:
> when ext4 filesystem is created with 64k block size, ^extent and
> ^huge_file features. the upper_limit would underflow during the
> computations in ext4_max_bitmap_size(). The problem is the size of block
> index tree for such large block size is more than i_blocks can carry.
> So fix the computation to count with this possibility. After this fix,
> the 'res' cannot overflow loff_t on the extreme case of filesystem with
> huge_files and 64K block size, so this patch also revert commit
> 75ca6ad408f4 ("ext4: fix loff_t overflow in ext4_max_bitmap_size()").
>
> Signed-off-by: Zhang Yi <yi.zhang@xxxxxxxxxx>
Thanks! The patch looks good. Feel free to add:
Reviewed-by: Jan Kara <jack@xxxxxxx>
Honza
> ---
> v3->v2: rewrite change log and use ppb to compute 'res' blocks.
> v2->v1: use DIV_ROUND_UP_ULL instead of DIV_ROUND_UP.
>
> fs/ext4/super.c | 46 +++++++++++++++++++++++++++++++---------------
> 1 file changed, 31 insertions(+), 15 deletions(-)
>
> diff --git a/fs/ext4/super.c b/fs/ext4/super.c
> index c5021ca0a28a..bfba62206a14 100644
> --- a/fs/ext4/super.c
> +++ b/fs/ext4/super.c
> @@ -3468,8 +3468,9 @@ 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
> @@ -3501,27 +3502,42 @@ static loff_t ext4_max_bitmap_size(int bits, int has_huge_files)
>
> }
>
> + /* Compute how many blocks we can address by block tree */
> + res += ppb;
> + res += ppb * ppb;
> + res += ((loff_t)ppb) * ppb * ppb;
> + /* 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 */
> - 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;
> -
> - res += 1LL << (bits-2);
> - res += 1LL << (2*(bits-2));
> - res += 1LL << (3*(bits-2));
> + if (upper_limit < ppb * ppb) {
> + meta_blocks += 1 + DIV_ROUND_UP_ULL(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_ULL(upper_limit, ppb) +
> + DIV_ROUND_UP_ULL(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,
> --
> 2.31.1
>
--
Jan Kara <jack@xxxxxxxx>
SUSE Labs, CR
