Re: [PATCH] NFC: hci: Split memcpy() of struct hcp_message flexible array

[Gustavo A. R. Silva]

On Fri, Sep 23, 2022 at 09:08:35PM -0700, Kees Cook wrote:
> 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@xxxxxxxxxxxx/
> 
> Cc: Krzysztof Kozlowski <krzysztof.kozlowski@xxxxxxxxxx>
> Cc: "David S. Miller" <davem@xxxxxxxxxxxxx>
> Cc: Eric Dumazet <edumazet@xxxxxxxxxx>
> Cc: Jakub Kicinski <kuba@xxxxxxxxxx>
> Cc: Paolo Abeni <pabeni@xxxxxxxxxx>
> Cc: netdev@xxxxxxxxxxxxxxx
> Reported-by: "Gustavo A. R. Silva" <gustavoars@xxxxxxxxxx>
> Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>

Reviewed-by: Gustavo A. R. Silva <gustavoars@xxxxxxxxxx>

Thanks!
--
Gustavo

> ---
>  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
>