netdev - [PATCH 18/64] cxgb3: Use struct_group() for memcpy() region

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Message-Id: <20210727205855.411487-19-keescook@chromium.org>
Date:   Tue, 27 Jul 2021 13:58:09 -0700
From:   Kees Cook <keescook@...omium.org>
To:     linux-hardening@...r.kernel.org
Cc:     Kees Cook <keescook@...omium.org>,
        "Gustavo A. R. Silva" <gustavoars@...nel.org>,
        Keith Packard <keithpac@...zon.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-kernel@...r.kernel.org, linux-wireless@...r.kernel.org,
        netdev@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        linux-staging@...ts.linux.dev, linux-block@...r.kernel.org,
        linux-kbuild@...r.kernel.org, clang-built-linux@...glegroups.com
Subject: [PATCH 18/64] cxgb3: Use struct_group() for memcpy() region

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() in struct rss_hdr around members imm_data and intr_gen,
so they can be referenced together. This will allow memcpy() and sizeof()
to more easily reason about sizes, improve readability, and avoid future
warnings about writing beyond the end of imm_data.

"pahole" shows no size nor member offset changes to struct rss_hdr.
"objdump -d" shows no object code changes.

Signed-off-by: Kees Cook <keescook@...omium.org>
---
 drivers/net/ethernet/chelsio/cxgb3/sge.c | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/drivers/net/ethernet/chelsio/cxgb3/sge.c b/drivers/net/ethernet/chelsio/cxgb3/sge.c
index cb5c79c43bc9..1ab1bd86a3a6 100644
--- a/drivers/net/ethernet/chelsio/cxgb3/sge.c
+++ b/drivers/net/ethernet/chelsio/cxgb3/sge.c
@@ -126,8 +126,10 @@ struct rsp_desc {		/* response queue descriptor */
 	struct rss_header rss_hdr;
 	__be32 flags;
 	__be32 len_cq;
-	u8 imm_data[47];
-	u8 intr_gen;
+	struct_group(immediate,
+		u8 imm_data[47];
+		u8 intr_gen;
+	);
 };
 
 /*
@@ -929,7 +931,8 @@ static inline struct sk_buff *get_imm_packet(const struct rsp_desc *resp)
 
 	if (skb) {
 		__skb_put(skb, IMMED_PKT_SIZE);
-		skb_copy_to_linear_data(skb, resp->imm_data, IMMED_PKT_SIZE);
+		BUILD_BUG_ON(IMMED_PKT_SIZE != sizeof(resp->immediate));
+		skb_copy_to_linear_data(skb, &resp->immediate, IMMED_PKT_SIZE);
 	}
 	return skb;
 }
-- 
2.30.2