On Tue, Jun 2, 2020 at 4:05 AM Victor Julien <victor@xxxxxxxxxxxx> wrote:
>
> Introduce a new flag (TP_STATUS_CSUM_UNNECESSARY) to indicate
> that the driver has completely validated the checksums in the packet.
>
> The TP_STATUS_CSUM_UNNECESSARY flag differs from TP_STATUS_CSUM_VALID
> in that the new flag will only be set if all the layers are valid,
> while TP_STATUS_CSUM_VALID is set as well if only the IP layer is valid.
transport, not ip checksum.
But as I understand it drivers set CHECKSUM_COMPLETE if they fill in
skb->csum over the full length of the packet. This does not
necessarily imply that any of the checksum fields in the packet are
valid yet (see also skb->csum_valid). Protocol code later compares
checksum fields against this using __skb_checksum_validate_complete and friends.
But packet sockets may be called before any of this, however. So I wonder
how valid the checksum really is right now when setting TP_STATUS_CSUM_VALID.
I assume it's correct, but don't fully understand where the validation
has taken place..
Similar to commit 682f048bd494 ("af_packet: pass checksum validation
status to the user"), please update tpacket_rcv and packet_rcv.
Note also that net-next is currently closed.
> for convenience there are also the following defines::
>
> diff --git a/include/uapi/linux/if_packet.h b/include/uapi/linux/if_packet.h
> index 3d884d68eb30..76a5c762e2e0 100644
> --- a/include/uapi/linux/if_packet.h
> +++ b/include/uapi/linux/if_packet.h
> @@ -113,6 +113,7 @@ struct tpacket_auxdata {
> #define TP_STATUS_BLK_TMO (1 << 5)
> #define TP_STATUS_VLAN_TPID_VALID (1 << 6) /* auxdata has valid tp_vlan_tpid */
> #define TP_STATUS_CSUM_VALID (1 << 7)
> +#define TP_STATUS_CSUM_UNNECESSARY (1 << 8)
>
> /* Tx ring - header status */
> #define TP_STATUS_AVAILABLE 0
> diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c
> index 29bd405adbbd..94e213537646 100644
> --- a/net/packet/af_packet.c
> +++ b/net/packet/af_packet.c
> @@ -2215,10 +2215,13 @@ static int tpacket_rcv(struct sk_buff *skb, struct net_device *dev,
>
> if (skb->ip_summed == CHECKSUM_PARTIAL)
> status |= TP_STATUS_CSUMNOTREADY;
> - else if (skb->pkt_type != PACKET_OUTGOING &&
> - (skb->ip_summed == CHECKSUM_COMPLETE ||
> - skb_csum_unnecessary(skb)))
> - status |= TP_STATUS_CSUM_VALID;
> + else if (skb->pkt_type != PACKET_OUTGOING) {
> + if (skb->ip_summed == CHECKSUM_UNNECESSARY)
> + status |= TP_STATUS_CSUM_UNNECESSARY | TP_STATUS_CSUM_VALID;
> + else if (skb->ip_summed == CHECKSUM_COMPLETE ||
> + skb_csum_unnecessary(skb))
> + status |= TP_STATUS_CSUM_VALID;
> + }
>
> if (snaplen > res)
> snaplen = res;
> --
> 2.17.1
>
