linux-kernel - [PATCH] net/ncsi: Silence runtime memcpy() false positive warning

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Date:   Fri,  2 Dec 2022 13:24:22 -0800
From:   Kees Cook <keescook@...omium.org>
To:     Samuel Mendoza-Jonas <sam@...dozajonas.com>
Cc:     Kees Cook <keescook@...omium.org>, Joel Stanley <joel@....id.au>,
        "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,
        linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: [PATCH] net/ncsi: Silence runtime memcpy() false positive warning

The memcpy() in ncsi_cmd_handler_oem deserializes nca->data into a
flexible array structure that overlapping with non-flex-array members
(mfr_id) intentionally. Since the mem_to_flex() API is not finished,
temporarily silence this warning, since it is a false positive, using
unsafe_memcpy().

Reported-by: Joel Stanley <joel@....id.au>
Link: https://lore.kernel.org/netdev/CACPK8Xdfi=OJKP0x0D1w87fQeFZ4A2DP2qzGCRcuVbpU-9=4sQ@mail.gmail.com/
Cc: Samuel Mendoza-Jonas <sam@...dozajonas.com>
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
Signed-off-by: Kees Cook <keescook@...omium.org>
---
 net/ncsi/ncsi-cmd.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/net/ncsi/ncsi-cmd.c b/net/ncsi/ncsi-cmd.c
index dda8b76b7798..fd2236ee9a79 100644
--- a/net/ncsi/ncsi-cmd.c
+++ b/net/ncsi/ncsi-cmd.c
@@ -228,7 +228,8 @@ static int ncsi_cmd_handler_oem(struct sk_buff *skb,
 	len += max(payload, padding_bytes);
 
 	cmd = skb_put_zero(skb, len);
-	memcpy(&cmd->mfr_id, nca->data, nca->payload);
+	unsafe_memcpy(&cmd->mfr_id, nca->data, nca->payload,
+		      /* skb allocated with enough to load the payload */);
 	ncsi_cmd_build_header(&cmd->cmd.common, nca);
 
 	return 0;
-- 
2.34.1