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

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Message-ID: <CACT4Y+aJb4u+KPAF7629YDb2tB2geZrQm5sFR3M+r2P1rgicwQ@mail.gmail.com>
Date:   Thu, 20 Jul 2023 17:27:57 +0200
From:   Dmitry Vyukov <dvyukov@...gle.com>
To:     Viacheslav Dubeyko <slava@...eyko.com>
Cc:     Matthew Wilcox <willy@...radead.org>,
        Arnd Bergmann <arnd@...db.de>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        syzbot <syzbot+7bb7cd3595533513a9e7@...kaller.appspotmail.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        christian.brauner@...ntu.com,
        Damien Le Moal <damien.lemoal@...nsource.wdc.com>,
        Jeff Layton <jlayton@...nel.org>,
        Linux FS Devel <linux-fsdevel@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        syzkaller-bugs@...glegroups.com,
        ZhangPeng <zhangpeng362@...wei.com>,
        linux-m68k@...ts.linux-m68k.org
Subject: Re: [syzbot] [hfs?] WARNING in hfs_write_inode

On Thu, 5 Jan 2023 at 17:45, Viacheslav Dubeyko <slava@...eyko.com> wrote:
> > On Wed, Jan 04, 2023 at 08:37:16PM -0800, Viacheslav Dubeyko wrote:
> >> Also, as far as I can see, available volume in report (mount_0.gz) somehow corrupted already:
> >
> > Syzbot generates deliberately-corrupted (aka fuzzed) filesystem images.
> > So basically, you can't trust anything you read from the disc.
> >
>
> If the volume has been deliberately corrupted, then no guarantee that file system
> driver will behave nicely. Technically speaking, inode write operation should never
> happened for corrupted volume because the corruption should be detected during
> b-tree node initialization time. If we would like to achieve such nice state of HFS/HFS+
> drivers, then it requires a lot of refactoring/implementation efforts. I am not sure that
> it is worth to do because not so many guys really use HFS/HFS+ as the main file
> system under Linux.


Most popular distros will happily auto-mount HFS/HFS+ from anything
inserted into USB (e.g. what one may think is a charger). This creates
interesting security consequences for most Linux users.
An image may also be corrupted non-deliberately, which will lead to
random memory corruptions if the kernel trusts it blindly.