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

Kees Cook
2021-07-31T16:07:26Z

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