[PATCH 42/64] net: qede: Use memset_after() for counters

[PATCH 42/64] net: qede: Use memset_after() for counters

[Kees Cook]

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?
---
 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);
 err3:
 	qede_napi_disable_remove(edev);
 err2:
-- 
2.30.2

Re: [PATCH 42/64] net: qede: Use memset_after() for counters

[Kees Cook]

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?

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:

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.

-Kees

> ---
>  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);
>  err3:
>  	qede_napi_disable_remove(edev);
>  err2:
> -- 
> 2.30.2
> 

-- 
Kees Cook

Re: [PATCH 42/64] net: qede: Use memset_after() for counters

[Kees Cook]

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@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?
> > 
> > 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