linux-kernel - Re: [PATCH v2] f2fs: avoid wrong decrypted data from disk

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Date:   Wed, 29 Aug 2018 21:03:31 -0700
From:   Jaegeuk Kim <jaegeuk@...nel.org>
To:     Chao Yu <yuchao0@...wei.com>
Cc:     linux-kernel@...r.kernel.org,
        linux-f2fs-devel@...ts.sourceforge.net
Subject: Re: [PATCH v2] f2fs: avoid wrong decrypted data from disk

On 08/30, Chao Yu wrote:
> On 2018/8/30 9:48, Jaegeuk Kim wrote:
> > 1. Create a file in an encrypted directory
> > 2. Do GC & drop caches
> > 3. Read stale data before its bio for metapage was not issued yet
> > 
> > Signed-off-by: Jaegeuk Kim <jaegeuk@...nel.org>
> > ---
> > Change log from v1:
> >  - move to bio != NULL
> > 
> >  fs/f2fs/data.c | 6 ++++++
> >  1 file changed, 6 insertions(+)
> > 
> > diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
> > index 382c1ef9a9e4..159e411785e9 100644
> > --- a/fs/f2fs/data.c
> > +++ b/fs/f2fs/data.c
> > @@ -1556,6 +1556,12 @@ static int f2fs_mpage_readpages(struct address_space *mapping,
> >  				bio = NULL;
> >  				goto set_error_page;
> >  			}
> > +		} else if (unlikely(f2fs_encrypted_file(inode))) {
> 
> For android scenario, encryption becomes a common case now, so I think we can
> remove unlikely here.
> 
> > +			/*
> > +			 * If the page is under writeback, we need to wait for
> > +			 * its completion to see the correct decrypted data.
> > +			 */
> > +			f2fs_wait_on_block_writeback(F2FS_I_SB(inode), block_nr);
> >  		}
> 
> Look at this again, it seems f2fs_wait_on_block_writeback() is not related to
> f2fs_grab_read_bio(), so we can move it here to make code logic more clear:
> 
> if (f2fs_encrypted_file(inode)) {
> 	/* */
> 	f2fs_wait_on_block_writeback(F2FS_I_SB(inode), block_nr);
> }
> 
> Also, in f2fs_submit_page_read(), we need to adjust to:
> 
> - f2fs_grab_read_bio()
> - f2fs_wait_on_block_writeback()
> - bio_add_page()
> 
> How do you think?

Oh, yeah!

> 
> Thanks,
> 
> >  
> >  		if (bio_add_page(bio, page, blocksize, 0) < blocksize)
> >