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Subject: Re: [syzbot] [hfs?] WARNING in hfs_write_inode
To:     Linus Torvalds <torvalds@linux-foundation.org>
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Cc:     Arnd Bergmann <arnd@arndb.de>,
        syzbot <syzbot+7bb7cd3595533513a9e7@syzkaller.appspotmail.com>,
        Andrew Morton <akpm@linux-foundation.org>,
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        Damien Le Moal <damien.lemoal@opensource.wdc.com>,
        jlayton@kernel.org, linux-fsdevel@vger.kernel.org,
        linux-kernel@vger.kernel.org, syzkaller-bugs@googlegroups.com,
        Matthew Wilcox <willy@infradead.org>,
        ZhangPeng <zhangpeng362@huawei.com>,
        Viacheslav Dubeyko <slava@dubeyko.com>,
        linux-m68k@lists.linux-m68k.org, flar@allandria.com
From:   Michael Schmitz <schmitzmic@gmail.com>
Message-ID: <baced5a3-31a3-d104-bf31-87d75fecb8e9@gmail.com>
Date:   Fri, 6 Jan 2023 20:09:11 +1300
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Hi Linus,

Am 06.01.2023 um 12:46 schrieb Michael Schmitz:
> Hi Linus,
>
> Am 06.01.2023 um 10:53 schrieb Linus Torvalds:
>> On Thu, Jan 5, 2023 at 1:35 PM Michael Schmitz <schmitzmic@gmail.com>
>> wrote:
>>>
>>> Looking at Linus' patch, I wonder whether the missing fd.entrylength
>>> size test in the HFS_IS_RSRC(inode) case was due to the fact that a
>>> file's resource fork may be empty?
>>
>> But if that is the case, then the subsequent hfs_bnode_read would
>> return garbage, no? And then writing it back after the update would be
>> even worse.
>>
>> So adding that
>>
>> +               if (fd.entrylength < sizeof(struct hfs_cat_file))
>> +                       goto out;
>>
>> would seem to be the right thing anyway. No?
>
> Yes, it would seem to be the right thing (in order to avoid further
> corrupting HFS data structures). Returning -EIO might cause a regression
> though.

A brief test on a HFS filesystem image (copy of my yaboot bootstrap 
partition) did not show any regression, so your patch appears to be just 
fine as-is.

Cheers,

	Michael