netdev - Re: [PATCH net] cfg80211: fix callback type mismatches in wext-compat

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Message-ID: <202011201118.CE625B965@keescook>
Date:   Fri, 20 Nov 2020 11:26:58 -0800
From:   Kees Cook <keescook@...omium.org>
To:     Sami Tolvanen <samitolvanen@...gle.com>
Cc:     Johannes Berg <johannes@...solutions.net>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        linux-wireless@...r.kernel.org, netdev@...r.kernel.org,
        LKML <linux-kernel@...r.kernel.org>,
        Sedat Dilek <sedat.dilek@...il.com>
Subject: Re: [PATCH net] cfg80211: fix callback type mismatches in wext-compat

On Tue, Nov 17, 2020 at 02:07:43PM -0800, Sami Tolvanen wrote:
> On Tue, Nov 17, 2020 at 1:45 PM Kees Cook <keescook@...omium.org> wrote:
> >
> > On Tue, Nov 17, 2020 at 12:59:02PM -0800, Sami Tolvanen wrote:
> > > Instead of casting callback functions to type iw_handler, which trips
> > > indirect call checking with Clang's Control-Flow Integrity (CFI), add
> > > stub functions with the correct function type for the callbacks.
> >
> > Oh, wow. iw_handler with union iwreq_data look like really nasty hacks.
> > Aren't those just totally bypassing type checking? Where do the
> > callbacks actually happen? I couldn't find them...
> 
> The callbacks to these happen in ioctl_standard_call in wext-core.c.

Thanks! If this is all the 'old compat' code, this patch looks fine. I
think new stuff should probably encode types in some fashion (rather
than via wrappers).

-- 
Kees Cook