Message ID | 20220225102837.3048196-1-yi.zhang@huawei.com |
---|---|
State | Superseded |
Headers | show |
Series | [v2] ext4: fix underflow in ext4_max_bitmap_size() | expand |
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@huawei.com> 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
On 2022/2/25 20:38, Jan Kara wrote: > 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@huawei.com> > > 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? Thanks for the review. Yes, I will rewrite the change log. > > 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? > If upper_limit==(1 << 48) - 1, we could address the whole data blocks, the 'res' is equal to EXT4_NDIR_BLOCKS + ppb + ppb*ppb + ((long long)ppb)*ppb*ppb, it's smaller than (1 << 43) - 1, so res << 16 is still smaller 1 << 59, so it cannot overflow loff_t again. Thanks, Yi.
On Sat 26-02-22 10:30:31, Zhang Yi wrote: > On 2022/2/25 20:38, Jan Kara wrote: > > On Fri 25-02-22 18:28:37, Zhang Yi wrote: > >> + /* 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? > > > > If upper_limit==(1 << 48) - 1, we could address the whole data blocks, the 'res' > is equal to EXT4_NDIR_BLOCKS + ppb + ppb*ppb + ((long long)ppb)*ppb*ppb, it's > smaller than (1 << 43) - 1, so res << 16 is still smaller 1 << 59, so it cannot > overflow loff_t again. Indeed, sorry for confusion. Not sure where I did mistake in my math previously. Honza
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)); + /* 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; - 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,
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@huawei.com> --- v2->v1: use DIV_ROUND_UP_ULL instead of DIV_ROUND_UP. fs/ext4/super.c | 46 +++++++++++++++++++++++++++++++--------------- 1 file changed, 31 insertions(+), 15 deletions(-)