linux-kernel - [PATCH] w1: Split memcpy() of struct cn

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Message-Id: <20220927003927.1942170-1-keescook@chromium.org>
Date:   Mon, 26 Sep 2022 17:39:27 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Evgeniy Polyakov <zbr@...emap.net>
Cc:     Kees Cook <keescook@...omium.org>, linux-kernel@...r.kernel.org,
        linux-hardening@...r.kernel.org
Subject: [PATCH] w1: Split memcpy() of struct cn_msg 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.

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

Cc: Evgeniy Polyakov <zbr@...emap.net>
Signed-off-by: Kees Cook <keescook@...omium.org>
---
 drivers/w1/w1_netlink.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/w1/w1_netlink.c b/drivers/w1/w1_netlink.c
index fa490aa4407c..db110cc442b1 100644
--- a/drivers/w1/w1_netlink.c
+++ b/drivers/w1/w1_netlink.c
@@ -611,7 +611,8 @@ static void w1_cn_callback(struct cn_msg *cn, struct netlink_skb_parms *nsp)
 		}
 		atomic_set(&block->refcnt, 1);
 		block->portid = nsp->portid;
-		memcpy(&block->request_cn, cn, sizeof(*cn) + cn->len);
+		block->request_cn = *cn;
+		memcpy(block->request_cn.data, cn->data, cn->len);
 		node = (struct w1_cb_node *)(block->request_cn.data + cn->len);
 
 		/* Sneeky, when not bundling, reply_size is the allocated space
-- 
2.34.1