netdev - Re: [PATCH 42/64] net: qede: Use memset

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Date:   Mon, 2 Aug 2021 09:23:24 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Shai Malin <smalin@...vell.com>
Cc:     "Gustavo A. R. Silva" <gustavoars@...nel.org>,
        Keith Packard <keithpac@...zon.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-wireless@...r.kernel.org" <linux-wireless@...r.kernel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
        "linux-staging@...ts.linux.dev" <linux-staging@...ts.linux.dev>,
        "linux-block@...r.kernel.org" <linux-block@...r.kernel.org>,
        "linux-kbuild@...r.kernel.org" <linux-kbuild@...r.kernel.org>,
        "clang-built-linux@...glegroups.com" 
        <clang-built-linux@...glegroups.com>,
        "linux-hardening@...r.kernel.org" <linux-hardening@...r.kernel.org>,
        GR-everest-linux-l2 <GR-everest-linux-l2@...vell.com>,
        Ariel Elior <aelior@...vell.com>
Subject: Re: [PATCH 42/64] net: qede: Use memset_after() for counters

On Mon, Aug 02, 2021 at 02:29:28PM +0000, Shai Malin wrote:
> 
> On Tue, Jul 31, 2021 at 07:07:00PM -0300, Kees Cook wrote:
> > On Tue, Jul 27, 2021 at 01:58:33PM -0700, Kees Cook wrote:
> > > In preparation for FORTIFY_SOURCE performing compile-time and run-time
> > > field bounds checking for memset(), avoid intentionally writing across
> > > neighboring fields.
> > >
> > > Use memset_after() so memset() doesn't get confused about writing
> > > beyond the destination member that is intended to be the starting point
> > > of zeroing through the end of the struct.
> > >
> > > Signed-off-by: Kees Cook <keescook@...omium.org>
> > > ---
> > > The old code seems to be doing the wrong thing: starting from not the
> > > first member, but sized for the whole struct. Which is correct?
> > 
> > Quick ping on this question.
> > 
> > The old code seems to be doing the wrong thing: it starts from the second
> > member and writes beyond int_info, clobbering qede_lock:
> 
> Thanks for highlighting the problem, but actually, the memset is redundant.
> We will remove it so the change will not be needed.
> 
> > 
> > struct qede_dev {
> >         ...
> >         struct qed_int_info             int_info;
> > 
> >         /* Smaller private variant of the RTNL lock */
> >         struct mutex                    qede_lock;
> >         ...
> > 
> > 
> > struct qed_int_info {
> >         struct msix_entry       *msix;
> >         u8                      msix_cnt;
> > 
> >         /* This should be updated by the protocol driver */
> >         u8                      used_cnt;
> > };
> > 
> > Should this also clear the "msix" member, or should this not write
> > beyond int_info? This patch does the latter.
> 
> It should clear only the msix_cnt, no need to clear the entire 
> qed_int_info structure.

Should used_cnt be cleared too? It is currently. Better yet, what patch
do you suggest I replace this proposed one with? :)

Thanks for looking at this!

-Kees

-- 
Kees Cook