linux-hardening - Re: [PATCH] mptcp: Use struct_group() to avoid cross-field memset()

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Date:   Fri, 21 Jan 2022 12:44:55 -0800 (PST)
From:   Mat Martineau <mathew.j.martineau@...ux.intel.com>
To:     Kees Cook <keescook@...omium.org>
cc:     Matthieu Baerts <matthieu.baerts@...sares.net>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>, netdev@...r.kernel.org,
        mptcp@...ts.linux.dev, linux-kernel@...r.kernel.org,
        linux-hardening@...r.kernel.org
Subject: Re: [PATCH] mptcp: Use struct_group() to avoid cross-field
 memset()

On Thu, 20 Jan 2022, Kees Cook wrote:

> In preparation for FORTIFY_SOURCE performing compile-time and run-time
> field bounds checking for memcpy(), memmove(), and memset(), avoid
> intentionally writing across neighboring fields.
>
> Use struct_group() to capture the fields to be reset, so that memset()
> can be appropriately bounds-checked by the compiler.
>
> Cc: Mat Martineau <mathew.j.martineau@...ux.intel.com>
> Cc: Matthieu Baerts <matthieu.baerts@...sares.net>
> Cc: "David S. Miller" <davem@...emloft.net>
> Cc: Jakub Kicinski <kuba@...nel.org>
> Cc: netdev@...r.kernel.org
> Cc: mptcp@...ts.linux.dev
> Signed-off-by: Kees Cook <keescook@...omium.org>
> ---
> net/mptcp/protocol.h | 6 +++---
> 1 file changed, 3 insertions(+), 3 deletions(-)
>

Thanks Kees, looks good to me. I checked around for other MPTCP structs 
that would need similar attention and didn't see any.

Reviewed-by: Mat Martineau <mathew.j.martineau@...ux.intel.com>


> diff --git a/net/mptcp/protocol.h b/net/mptcp/protocol.h
> index 0e6b42c76ea0..85317ce38e3f 100644
> --- a/net/mptcp/protocol.h
> +++ b/net/mptcp/protocol.h
> @@ -408,7 +408,7 @@ DECLARE_PER_CPU(struct mptcp_delegated_action, mptcp_delegated_actions);
> struct mptcp_subflow_context {
> 	struct	list_head node;/* conn_list of subflows */
>
> -	char	reset_start[0];
> +	struct_group(reset,
>
> 	unsigned long avg_pacing_rate; /* protected by msk socket lock */
> 	u64	local_key;
> @@ -458,7 +458,7 @@ struct mptcp_subflow_context {
>
> 	long	delegated_status;
>
> -	char	reset_end[0];
> +	);
>
> 	struct	list_head delegated_node;   /* link into delegated_action, protected by local BH */
>
> @@ -494,7 +494,7 @@ mptcp_subflow_tcp_sock(const struct mptcp_subflow_context *subflow)
> static inline void
> mptcp_subflow_ctx_reset(struct mptcp_subflow_context *subflow)
> {
> -	memset(subflow->reset_start, 0, subflow->reset_end - subflow->reset_start);
> +	memset(&subflow->reset, 0, sizeof(subflow->reset));
> 	subflow->request_mptcp = 1;
> }
>
> -- 
> 2.30.2
>
>

--
Mat Martineau
Intel