linux-ext4 - Re: [syzbot] WARNING in iomap

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Message-ID: <YwOYMJrvBuoVye7R@casper.infradead.org>
Date:   Mon, 22 Aug 2022 15:52:32 +0100
From:   Matthew Wilcox <willy@...radead.org>
To:     Siddh Raman Pant <code@...dh.me>
Cc:     david <david@...morbit.com>, djwong <djwong@...nel.org>,
        fgheet255t <fgheet255t@...il.com>, hch <hch@...radead.org>,
        linux-ext4 <linux-ext4@...r.kernel.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        linux-xfs <linux-xfs@...r.kernel.org>,
        riteshh <riteshh@...ux.ibm.com>,
        syzbot+a8e049cd3abd342936b6 
        <syzbot+a8e049cd3abd342936b6@...kaller.appspotmail.com>,
        syzkaller-bugs <syzkaller-bugs@...glegroups.com>
Subject: Re: [syzbot] WARNING in iomap_iter

On Mon, Aug 22, 2022 at 08:19:43PM +0530, Siddh Raman Pant wrote:
> On Mon, 22 Aug 2022 20:15:28 +0530  Matthew Wilcox  wrote:
> > On Sun, Aug 21, 2022 at 05:18:16PM +0530, Siddh Raman Pant wrote:
> > > @@ -979,9 +979,15 @@ loop_set_status_from_info(struct loop_device *lo,
> > >  
> > >       lo->lo_offset = info->lo_offset;
> > >       lo->lo_sizelimit = info->lo_sizelimit;
> > > +     lo->lo_flags = info->lo_flags;
> > > +
> > > +     /* loff_t/int vars are assigned __u64/__u32 vars (respectively) */
> > > +     if (lo->lo_offset < 0 || lo->lo_sizelimit < 0 || lo->lo_flags < 0)
> > > +             return -EOVERFLOW;
> > 
> > Why would you check lo_flags?  That really, really should be an unsigned
> > type.
> 
> I agree, but the loop_device struct has (see line 54 of loop.c):
>         int             lo_flags;
> 
> Thus, I checked for it, as we are not changing any types.

But it's not an integer.  It's a bitfield.  Nobody checks lo_flags for
"is it less than zero".  That makes it very different from lo_offset.