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

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Message-ID: <YPhbU/umyUZLdxIw@casper.infradead.org>
Date:   Wed, 21 Jul 2021 18:37:23 +0100
From:   Matthew Wilcox <willy@...radead.org>
To:     butt3rflyh4ck <butterflyhuangxx@...il.com>
Cc:     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 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).