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

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Date:   Wed, 21 Jul 2021 12:14:16 -0700
From:   "Darrick J. Wong" <djwong@...nel.org>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     butt3rflyh4ck <butterflyhuangxx@...il.com>,
        LKML <linux-kernel@...r.kernel.org>,
        linux-fsdevel@...r.kernel.org,
        syzkaller-bugs <syzkaller-bugs@...glegroups.com>
Subject: Re: A shift-out-of-bounds in minix_statfs in fs/minix/inode.c

On Wed, Jul 21, 2021 at 06:37:23PM +0100, Matthew Wilcox 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?  That's not something we're
> traditionally interested in, unless the filesystem is one customarily
> used for data interchange (like FAT or iso9660).

Sounds to me like butt3rflyh4ck is volunteering to rebuild fs/minix with
proper ondisk metadata buffer verifiers.

--D