On Fri 25-02-22 18:28:37, Zhang Yi wrote:
> The same to commit 1c2d14212b15 ("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 75ca6ad408f4 ("ext4: fix loff_t overflow in ext4_max_bitmap_size()")
> because it's no longer needed.
>
> Signed-off-by: Zhang Yi <yi.zhang@xxxxxxxxxx>
Thanks for the patch. I would not refer to ext2 patch in the changelog - it
is better to have it self-contained. AFAIU the problem is that (meta_blocks
> upper_limit) for 64k blocksize and ^huge_file and so upper_limit would
underflow during the computations, am I right?
Also two comments below:
> diff --git a/fs/ext4/super.c b/fs/ext4/super.c
> index c5021ca0a28a..95608c2127e7 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)
>
> }
>
> - /* 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));
When you have the 'ppb' convenience variable, perhaps you can update this
math to:
res = EXT4_NDIR_BLOCKS + ppb + ppb*ppb + ((long long)ppb)*ppb*ppb;
It is easier to understand and matches how you compute meta_blocks as well.
> + /* 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_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;
Cannot this overflow loff_t again? I mean if upper_limit == (1 << 48) - 1
and we have 64k blocksize, 'res' will be larger than (1 << 47) and thus
res << 16 will be greater than 1 << 63 => negative... Am I missing
something?
Honza
--
Jan Kara <jack@xxxxxxxx>
SUSE Labs, CR
