linux-hardening - Re: [PATCH] r8152: Avoid memcpy() over-reading of ETH_SS

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Date:   Wed, 16 Jun 2021 20:20:57 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Andrew Lunn <andrew@...n.ch>
Cc:     netdev@...r.kernel.org, "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Hayes Wang <hayeswang@...ltek.com>,
        Lee Jones <lee.jones@...aro.org>, EJ Hsu <ejh@...dia.com>,
        linux-kernel@...r.kernel.org, linux-usb@...r.kernel.org,
        linux-hardening@...r.kernel.org
Subject: Re: [PATCH] r8152: Avoid memcpy() over-reading of ETH_SS_STATS

On Wed, Jun 16, 2021 at 10:10:40PM +0200, Andrew Lunn wrote:
> On Wed, Jun 16, 2021 at 10:02:43PM +0200, Andrew Lunn wrote:
> > On Wed, Jun 16, 2021 at 12:53:03PM -0700, Kees Cook wrote:
> > > In preparation for FORTIFY_SOURCE performing compile-time and run-time
> > > field bounds checking for memcpy(), memmove(), and memset(), avoid
> > > intentionally reading across neighboring array fields.
> > > 
> > > The memcpy() is copying the entire structure, not just the first array.
> > > Adjust the source argument so the compiler can do appropriate bounds
> > > checking.
> > > 
> > > Signed-off-by: Kees Cook <keescook@...omium.org>
> > > ---
> > >  drivers/net/usb/r8152.c | 2 +-
> > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > > 
> > > diff --git a/drivers/net/usb/r8152.c b/drivers/net/usb/r8152.c
> > > index 85039e17f4cd..5f08720bf1c9 100644
> > > --- a/drivers/net/usb/r8152.c
> > > +++ b/drivers/net/usb/r8152.c
> > > @@ -8678,7 +8678,7 @@ static void rtl8152_get_strings(struct net_device *dev, u32 stringset, u8 *data)
> > >  {
> > >  	switch (stringset) {
> > >  	case ETH_SS_STATS:
> > > -		memcpy(data, *rtl8152_gstrings, sizeof(rtl8152_gstrings));
> > > +		memcpy(data, rtl8152_gstrings, sizeof(rtl8152_gstrings));
> > >  		break;
> > 
> > Is this correct? The call is supposed to return all the statistic
> > strings, which would be the entire structure.
> 
> Ah! now i think i get it.
> 
> Although *rtl8152_gstrings == rtl8152_gstrings in terms of addresses,
> the compiler sees that *rtl8152_gstrings is sizeof(ETH_GSTRING_LEN),
> but we are copying sizeof(rtl8152_gstrings), so it will issue a
> warning. So you remove the * to indicate we are interesting in the
> whole structure of arrays.

Right! Sorry if that wasn't more clear. :)

-- 
Kees Cook