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Subject[PATCH] NFC: hci: Split memcpy() of struct hcp_message flexible array
Date
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@linaro.org>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Eric Dumazet <edumazet@google.com>
Cc: Jakub Kicinski <kuba@kernel.org>
Cc: Paolo Abeni <pabeni@redhat.com>
Cc: netdev@vger.kernel.org
Reported-by: "Gustavo A. R. Silva" <gustavoars@kernel.org>
Signed-off-by: Kees Cook <keescook@chromium.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
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