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: Eric Dumazet <edumazet@google.com>
Cc: Paolo Abeni <pabeni@redhat.com>
Reported-by: "Gustavo A. R. Silva" <gustavoars@kernel.org>
Signed-off-by: Kees Cook <keescook@chromium.org>
Reviewed-by: Gustavo A. R. Silva <gustavoars@kernel.org>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/20220924040835.3364912-1-keescook@chromium.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/net/nfc/hci/hcp.c b/net/nfc/hci/hcp.c
index 05c6098..4902f50 100644 (file)
--- 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 */