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From:   Shai Malin <smalin@marvell.com>
To:     Kees Cook <keescook@chromium.org>
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Subject: Re: [PATCH 42/64] net: qede: Use memset_after() for counters
Thread-Topic: [PATCH 42/64] net: qede: Use memset_after() for counters
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Date:   Mon, 2 Aug 2021 14:29:28 +0000
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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@chromium.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?
>=20
> Quick ping on this question.
>=20
> 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.

>=20
> struct qede_dev {
>         ...
>         struct qed_int_info             int_info;
>=20
>         /* Smaller private variant of the RTNL lock */
>         struct mutex                    qede_lock;
>         ...
>=20
>=20
> struct qed_int_info {
>         struct msix_entry       *msix;
>         u8                      msix_cnt;
>=20
>         /* This should be updated by the protocol driver */
>         u8                      used_cnt;
> };
>=20
> 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=20
qed_int_info structure.

>=20
> -Kees
>=20
> > ---
> >  drivers/net/ethernet/qlogic/qede/qede_main.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/drivers/net/ethernet/qlogic/qede/qede_main.c
> b/drivers/net/ethernet/qlogic/qede/qede_main.c
> > index 01ac1e93d27a..309dfe8c94fb 100644
> > --- a/drivers/net/ethernet/qlogic/qede/qede_main.c
> > +++ b/drivers/net/ethernet/qlogic/qede/qede_main.c
> > @@ -2419,7 +2419,7 @@ static int qede_load(struct qede_dev *edev, enum
> qede_load_mode mode,
> >  	goto out;
> >  err4:
> >  	qede_sync_free_irqs(edev);
> > -	memset(&edev->int_info.msix_cnt, 0, sizeof(struct qed_int_info));
> > +	memset_after(&edev->int_info, 0, msix);

We will replace the redundant memset with:
edev->int_info.msix_cnt =3D 0;=20

> >  err3:
> >  	qede_napi_disable_remove(edev);
> >  err2:
> > --
> > 2.30.2
> >
>=20
> --
> Kees Cook