Re: [PATCH 3/4] f2fs: add inline encryption support

[Chao Yu <yuchao0@huawei.com>]

Hi Eric,

On 2020/6/19 2:13, Eric Biggers wrote:
> Hi Chao,
> 
> On Thu, Jun 18, 2020 at 06:06:02PM +0800, Chao Yu wrote:
>>> @@ -936,8 +972,11 @@ void f2fs_submit_page_write(struct f2fs_io_info *fio)
>>>  
>>>  	inc_page_count(sbi, WB_DATA_TYPE(bio_page));
>>>  
>>> -	if (io->bio && !io_is_mergeable(sbi, io->bio, io, fio,
>>> -			io->last_block_in_bio, fio->new_blkaddr))
>>> +	if (io->bio &&
>>> +	    (!io_is_mergeable(sbi, io->bio, io, fio, io->last_block_in_bio,
>>> +			      fio->new_blkaddr) ||
>>> +	     !f2fs_crypt_mergeable_bio(io->bio, fio->page->mapping->host,
>>> +				       fio->page->index, fio)))
>>
>> bio_page->index, fio)))
>>
>>>  		__submit_merged_bio(io);
>>>  alloc_new:
>>>  	if (io->bio == NULL) {
>>> @@ -949,6 +988,8 @@ void f2fs_submit_page_write(struct f2fs_io_info *fio)
>>>  			goto skip;
>>>  		}
>>>  		io->bio = __bio_alloc(fio, BIO_MAX_PAGES);
>>> +		f2fs_set_bio_crypt_ctx(io->bio, fio->page->mapping->host,
>>> +				       fio->page->index, fio, GFP_NOIO);
>>
>> bio_page->index, fio, GFP_NOIO);
>>
> 
> We're using ->mapping->host and ->index.  Ordinarily that would mean the page
> needs to be a pagecache page.  But bio_page can also be a compressed page or a
> bounce page containing fs-layer encrypted contents.

I'm concerning about compression + inlinecrypt case.

> 
> Is your suggestion to keep using fio->page->mapping->host (since encrypted pages

Yup,

> don't have a mapping), but start using bio_page->index (since f2fs apparently

I meant that we need to use bio_page->index as tweak value in write path to
keep consistent as we did in read path, otherwise we may read the wrong
decrypted data later to incorrect tweak value.

- f2fs_read_multi_pages (only comes from compression inode)
 - f2fs_alloc_dic
  - f2fs_set_compressed_page(page, cc->inode,
					start_idx + i + 1, dic);
                                        ^^^^^^^^^^^^^^^^^
  - dic->cpages[i] = page;
 - for ()
     struct page *page = dic->cpages[i];
     if (!bio)
       - f2fs_grab_read_bio(..., page->index,..)
        - f2fs_set_bio_crypt_ctx(..., first_idx, ..)   /* first_idx == cpage->index */

You can see that cpage->index was set to page->index + 1, that's why we need
to use one of cpage->index/page->index as tweak value all the time rather than
using both index mixed in read/write path.

But note that for fs-layer encryption, we have used cpage->index as tweak value,
so here I suggest we can keep consistent to use cpage->index in inlinecrypt case.

> *does* set ->index for compressed pages, and if the file uses fs-layer
> encryption then f2fs_set_bio_crypt_ctx() won't use the index anyway)?
> 
> Does this mean the code is currently broken for compression + inline encryption
> because it's using the wrong ->index?  I think the answer is no, since

I guess it's broken now for compression + inlinecrypt case.

> f2fs_write_compressed_pages() will still pass the first 'nr_cpages' pagecache
> pages along with the compressed pages.  In that case, your suggestion would be a
> cleanup rather than a fix?

That's a fix.

> 
> It would be helpful if there was an f2fs mount option to auto-enable compression
> on all files (similar to how test_dummy_encryption auto-enables encryption on
> all files) so that it could be tested more easily.

Agreed.

Previously I changed mkfs to allow to add compression flag to root inode for
compression test. :P

Thanks,

> 
> - Eric
> .
>