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List:       linux-hardening
Subject:    Re: [PATCH 42/64] net: qede: Use memset_after() for counters
From:       Kees Cook <keescook () chromium ! org>
Date:       2021-07-31 16:07:17
Message-ID: 202107310901.CB470B8C9D () keescook
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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


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