linux-kernel - Re: [PATCH] ntfs: change check order in ntfs_attr

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Message-Id: <20220826154231.6634-1-yin31149@gmail.com>
Date:   Fri, 26 Aug 2022 23:42:32 +0800
From:   Hawkins Jiawei <yin31149@...il.com>
To:     dan.carpenter@...cle.com
Cc:     akpm@...ux-foundation.org, anton@...era.com,
        chenxiaosong2@...wei.com, linux-kernel@...r.kernel.org,
        linux-ntfs-dev@...ts.sourceforge.net,
        syzbot+5f8dcabe4a3b2c51c607@...kaller.appspotmail.com,
        syzkaller-bugs@...glegroups.com, yin31149@...il.com
Subject: Re: [PATCH] ntfs: change check order in ntfs_attr_find

On Fri, 26 Aug 2022 at 23:15, Dan Carpenter <dan.carpenter@...cle.com> wrote:
>
> On Fri, Aug 26, 2022 at 08:32:57PM +0800, Hawkins Jiawei wrote:
> > > syz test https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
> > >
> > > Looks like it is improper check order that causes this bug.
> >
> > Sorry for wrong command.
> > #syz test https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
> >
> > diff --git a/fs/ntfs/attrib.c b/fs/ntfs/attrib.c
> > index 52615e6090e1..6480cd2d371d 100644
> > --- a/fs/ntfs/attrib.c
> > +++ b/fs/ntfs/attrib.c
> > @@ -594,10 +594,11 @@ static int ntfs_attr_find(const ATTR_TYPE type, const ntfschar *name,
> >       for (;; a = (ATTR_RECORD*)((u8*)a + le32_to_cpu(a->length))) {
> >               u8 *mrec_end = (u8 *)ctx->mrec +
> >                              le32_to_cpu(ctx->mrec->bytes_allocated);
> > +             if ((u8*)a < (u8*)ctx->mrec || (u8*)a > mrec_end)
> > +                     break;
>
> This definitely seems like a bug.  But your code won't build.  Syzbot
> must have -Werror turned off?
Hi Dan,
Did you mean we should put the variable declares at the beginning of the function?
(Correct me if I understand anything wrong)

>
> Btw, this was in the original code, but those casts are ugly.  Ideally
> there would be some way to get rid of them.  But otherwise at least
> put a space after the u8.  "(u8 *)a < (u8 *)ctx->mrec".
>
> >               u8 *name_end = (u8 *)a + le16_to_cpu(a->name_offset) +
> >                              a->name_length * sizeof(ntfschar);
> > -             if ((u8*)a < (u8*)ctx->mrec || (u8*)a > mrec_end ||
> > -                 name_end > mrec_end)
> > +             if (name_end > mrec_end)
> >                       break;
>
> regards,
> dan carpenter
So maybe I can try to refactor these codes. But I wonder if this can be
done in a seperate bug