Eric Dumazet wrote:
> build_udp_packet_csum() passes udph->len, which is in network byte
> order, as the number of bytes to checksum. On little-endian hosts this
> reads up to 64KB past the UDP header and computes a wrong checksum.
>
> Existing callers did not crash only because they use packet buffers
> of MAX_VNET_TUNNEL_PACKET_SZ bytes.
>
> Use ntohs(udph->len), as tap.c does in its own build_udp_packet().
>
> Fixes: a942fcd72e97 ("selftest: tun: Introduce tuntap_helpers.h header for
> TUN/TAP testing")
> Signed-off-by: Eric Dumazet <[email protected]>
Reviewed-by: Willem de Bruijn <[email protected]>
> ---
> tools/testing/selftests/net/tuntap_helpers.h | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/tools/testing/selftests/net/tuntap_helpers.h
> b/tools/testing/selftests/net/tuntap_helpers.h
> index d6c0437136ec..ac9b2da57a6d 100644
> --- a/tools/testing/selftests/net/tuntap_helpers.h
> +++ b/tools/testing/selftests/net/tuntap_helpers.h
> @@ -335,7 +335,7 @@ static inline void build_udp_packet_csum(uint8_t *buf,
> int family,
> sum += htons(IPPROTO_UDP) + udph->len;
>
> if (!csum_off)
> - sum += add_csum(buf, udph->len);
> + sum += add_csum(buf, ntohs(udph->len));
>
> udph->check = finish_ip_csum(sum);
If respinning: we probably should also do CSUM_MANGLED_0 conversion here.
And to zero udph->check first. All existing callers do. But the calloc in
patch 3/3 does not.
> }
> --
> 2.53.0
>
