linux-kernel - Re: [syzbot] [hfs?] WARNING in hfs_write

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Date:   Fri, 6 Jan 2023 20:09:11 +1300
From:   Michael Schmitz <schmitzmic@...il.com>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Arnd Bergmann <arnd@...db.de>,
        syzbot <syzbot+7bb7cd3595533513a9e7@...kaller.appspotmail.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        christian.brauner@...ntu.com,
        Damien Le Moal <damien.lemoal@...nsource.wdc.com>,
        jlayton@...nel.org, linux-fsdevel@...r.kernel.org,
        linux-kernel@...r.kernel.org, syzkaller-bugs@...glegroups.com,
        Matthew Wilcox <willy@...radead.org>,
        ZhangPeng <zhangpeng362@...wei.com>,
        Viacheslav Dubeyko <slava@...eyko.com>,
        linux-m68k@...ts.linux-m68k.org, flar@...andria.com
Subject: Re: [syzbot] [hfs?] WARNING in hfs_write_inode

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@...il.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