linux-kernel - Re: [PATCH] fs: jfs: fix shift-out-of-bounds in dbDiscardAG

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Date:   Tue, 25 Oct 2022 13:12:43 +0800
From:   Hoi Pok Wu <wuhoipok@...il.com>
To:     Dave Kleikamp <dave.kleikamp@...cle.com>
Cc:     jfs-discussion@...ts.sourceforge.net, linux-kernel@...r.kernel.org,
        syzbot+f0e0fcf3cd1047ae60ad@...kaller.appspotmail.com,
        syzkaller-bugs@...glegroups.com
Subject: Re: [PATCH] fs: jfs: fix shift-out-of-bounds in dbDiscardAG

Thanks for the suggestion! I will send a Patch V2 soon.


On Tue, Oct 25, 2022 at 5:05 AM Dave Kleikamp <dave.kleikamp@...cle.com> wrote:
>
> On 10/19/22 4:38AM, Hoi Pok Wu wrote:
> > Bug reported by syzbot, UBSAN: array-index-out-of-bounds in dbDiscardAG.
> > Fixed by simply rearranging agno_end smaller than MAXAG. However, I wonder if it
> > is a better idea to return -EINVAL, rejecting user input. Thank you.
>
> I don't think the problem is simply that the user input is bad, the
> range is already limited:
>
>          if (end >= bmp->db_mapsize)
>                  end = bmp->db_mapsize - 1;
>
> It seems syzbot corrupted some on-disk data structure to trigger this
> failure. It may be best to call jfs_error() and bail out.
>
> Thanks,
> Shaggy
>
> >
> > Reported-by: syzbot+f0e0fcf3cd1047ae60ad@...kaller.appspotmail.com
> > Signed-off-by: Hoi Pok Wu <wuhoipok@...il.com>
> > ---
> >   fs/jfs/jfs_discard.c | 4 ++++
> >   1 file changed, 4 insertions(+)
> >
> > diff --git a/fs/jfs/jfs_discard.c b/fs/jfs/jfs_discard.c
> > index 575cb2ba74fc..3101eaf3098a 100644
> > --- a/fs/jfs/jfs_discard.c
> > +++ b/fs/jfs/jfs_discard.c
> > @@ -96,6 +96,10 @@ int jfs_ioc_trim(struct inode *ip, struct fstrim_range *range)
> >        */
> >       agno = BLKTOAG(start, JFS_SBI(ip->i_sb));
> >       agno_end = BLKTOAG(end, JFS_SBI(ip->i_sb));
> > +
> > +     if (agno_end >= MAXAG)
> > +             agno_end = MAXAG - 1;
> > +
> >       while (agno <= agno_end) {
> >               trimmed += dbDiscardAG(ip, agno, minlen);
> >               agno++;