linux-kernel - Re: A shift-out-of-bounds in minix

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Message-ID: <CAFcO6XO0GR8GBVD7hT8VL5qey3cCYriMqvt0Dan72i5yVP6FxQ@mail.gmail.com>
Date:   Thu, 22 Jul 2021 10:43:10 +0800
From:   butt3rflyh4ck <butterflyhuangxx@...il.com>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     LKML <linux-kernel@...r.kernel.org>, linux-fsdevel@...r.kernel.org,
        syzkaller-bugs <syzkaller-bugs@...glegroups.com>,
        djwong@...nel.org
Subject: Re: A shift-out-of-bounds in minix_statfs in fs/minix/inode.c

On Thu, Jul 22, 2021 at 1:37 AM Matthew Wilcox <willy@...radead.org> wrote:
>
> On Thu, Jul 22, 2021 at 01:14:06AM +0800, butt3rflyh4ck wrote:
> > ms = (struct minix_super_block *) bh->b_data; /// --------------> set
> > minix_super_block pointer
> > sbi->s_ms = ms;
> > sbi->s_sbh = bh;
> > sbi->s_mount_state = ms->s_state;
> > sbi->s_ninodes = ms->s_ninodes;
> > sbi->s_nzones = ms->s_nzones;
> > sbi->s_imap_blocks = ms->s_imap_blocks;
> > sbi->s_zmap_blocks = ms->s_zmap_blocks;
> > sbi->s_firstdatazone = ms->s_firstdatazone;
> > sbi->s_log_zone_size = ms->s_log_zone_size;  // ------------------>
> > set sbi->s_log_zone_size
>

> So what you're saying is that if you construct a malicious minix image,
> you can produce undefined behaviour?

Yes, the attachment is a reproduction. just compile it and run.

>That's not something we're
> traditionally interested in, unless the filesystem is one customarily
> used for data interchange (like FAT or iso9660).
>

These file systems are my fuzzing targets.


Regards,
 butt3rflyh4ck.


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