linux-kernel - Re: [PATCH v8] misc: sgi-gru: fix use-after-free error in gru_set_context_option, gru_fault and gru_handle_user_call

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Date:   Wed, 9 Nov 2022 13:09:08 +0100
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Zheng Hacker <hackerzheng666@...il.com>
Cc:     Zheng Wang <zyytlz.wz@....com>, zhengyejian1@...wei.com,
        dimitri.sivanich@....com, arnd@...db.de,
        linux-kernel@...r.kernel.org, alex000young@...il.com,
        security@...nel.org, sivanich@....com, lkp@...el.com
Subject: Re: [PATCH v8] misc: sgi-gru: fix use-after-free error in
 gru_set_context_option, gru_fault and gru_handle_user_call_os

On Wed, Nov 09, 2022 at 08:04:04PM +0800, Zheng Hacker wrote:
> Greg KH <gregkh@...uxfoundation.org> 于2022年11月9日周三 19:12写道：
> > >       /*
> > >        * If the current task is the context owner, verify that the
> > > @@ -727,14 +728,16 @@ void gru_check_context_placement(struct gru_thread_state *gts)
> > >        */
> > >       gru = gts->ts_gru;
> > >       if (!gru || gts->ts_tgid_owner != current->tgid)
> > > -             return;
> > > +             return ret;
> >
> > Why does this check return "all is good!" ?
> >
> > Shouldn't that be an error?
> >
> This check is something like "if the gts has been initiiazed properly".
> If it's not, I thinks we shouldn't treat the gts like something very
> bad happend. Because in the later request, the gts can still have a
> chance to be configed/updated properly. This is different from "it's
> too bad so we have to unload gts right now". This is just my personal
> point of view. Besides, the caller of this function have token it into
> consider. In gru_fault, it will try again and in gru_handle_user_call_os,
> it will return -EAGAIN. In gru_set_context_option, it will be fine
> because there won't be any operation on gts->ts_gru or gts->ts_tgid_owner

Then you need to document it why this is "success" as it is not obvious
at all.

thanks,

greg k-h