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Date: Mon, 18 Jan 2021 21:59:16 +0800
From: Gao Xiang <hsiangkao@redhat.com>
To: Hu Weiwen <sehuww@mail.scut.edu.cn>
Subject: Re: [PATCH] erofs-utils: fix battach on full buffer block
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 <linux-erofs-bounces+linux-erofs=archiver.kernel.org@lists.ozlabs.org>

Hi Weiwen,

On Mon, Jan 18, 2021 at 08:39:45PM +0800, Hu Weiwen wrote:
> When __erofs_battach() is called on an buffer block of which
> (bb->buffers.off % EROFS_BLKSIZ == 0), `tail_blkaddr' will not be
> updated correctly. This bug can be reproduced by:
> 
> mkdir bug-repo
> head -c 4032 /dev/urandom > bug-repo/1
> head -c 4095 /dev/urandom > bug-repo/2
> head -c 12345 /dev/urandom > bug-repo/3  # arbitrary size
> mkfs.erofs -Eforce-inode-compact bug-repo.erofs.img bug-repo
> 
> Then mount this image and see that file `3' in the image is different
> from `bug-repo/3'.
> 
> This patch fix this by:
> 
> * Don't inline tail-end data in this case, since the tail-end data will
> be in a different block from inode.
> * Correctly handle `battach' in this case.
> 

I will evaluate this condition later, yet if you have some interest
and extra time, could you also help on writing a regression testcase
for this, so we can look after such regression in case of the future
code changes?

This is also an ongoing work for the next erofs-utils release, see:
https://git.kernel.org/pub/scm/linux/kernel/git/xiang/erofs-utils.git/

Thanks,
Gao Xiang