netdev - [PATCH] NFC: hci: Split memcpy() of struct hcp

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Message-Id: <20220924040835.3364912-1-keescook@chromium.org>
Date:   Fri, 23 Sep 2022 21:08:35 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
Cc:     Kees Cook <keescook@...omium.org>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>, netdev@...r.kernel.org,
        "Gustavo A. R. Silva" <gustavoars@...nel.org>,
        linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: [PATCH] NFC: hci: Split memcpy() of struct hcp_message flexible array

To work around a misbehavior of the compiler's ability to see into
composite flexible array structs (as detailed in the coming memcpy()
hardening series[1]), split the memcpy() of the header and the payload
so no false positive run-time overflow warning will be generated. This
split already existed for the "firstfrag" case, so just generalize the
logic further.

[1] https://lore.kernel.org/linux-hardening/20220901065914.1417829-2-keescook@chromium.org/

Cc: Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
Cc: "David S. Miller" <davem@...emloft.net>
Cc: Eric Dumazet <edumazet@...gle.com>
Cc: Jakub Kicinski <kuba@...nel.org>
Cc: Paolo Abeni <pabeni@...hat.com>
Cc: netdev@...r.kernel.org
Reported-by: "Gustavo A. R. Silva" <gustavoars@...nel.org>
Signed-off-by: Kees Cook <keescook@...omium.org>
---
 net/nfc/hci/hcp.c | 12 +++++-------
 1 file changed, 5 insertions(+), 7 deletions(-)

diff --git a/net/nfc/hci/hcp.c b/net/nfc/hci/hcp.c
index 05c60988f59a..4902f5064098 100644
--- a/net/nfc/hci/hcp.c
+++ b/net/nfc/hci/hcp.c
@@ -73,14 +73,12 @@ int nfc_hci_hcp_message_tx(struct nfc_hci_dev *hdev, u8 pipe,
 		if (firstfrag) {
 			firstfrag = false;
 			packet->message.header = HCP_HEADER(type, instruction);
-			if (ptr) {
-				memcpy(packet->message.data, ptr,
-				       data_link_len - 1);
-				ptr += data_link_len - 1;
-			}
 		} else {
-			memcpy(&packet->message, ptr, data_link_len);
-			ptr += data_link_len;
+			packet->message.header = *ptr++;
+		}
+		if (ptr) {
+			memcpy(packet->message.data, ptr, data_link_len - 1);
+			ptr += data_link_len - 1;
 		}
 
 		/* This is the last fragment, set the cb bit */
-- 
2.34.1