Hi,
In file vnet/ip/ip6_forward.c(VPP 21.01), function ip6_local_inline(), the
node's packet processing has the following check:
if (PREDICT_FALSE (need_csum))
{
flags = ip6_tcp_udp_icmp_validate_checksum (vm, b[0]);
good_l4_csum = flags & VNET_BUFFER_F_L4_CHECKSUM_CORRECT;
error = IP6_ERROR_UNKNOWN_PROTOCOL;
}
else
{
if (ip6_tcp_udp_icmp_bad_length (vm, b[0]))
error = IP6_ERROR_BAD_LENGTH;
}
Kindly explain the reason behind the checksum and the length validation being
under the if-else check, making the length validation not applicable for the
case when checksum validation is applicable.
Also, in the function ip6_tcp_udp_icmp_bad_length (refer the below snippet),
the function seems to assume that the hop-by-hop extension header shall always
be present. Is it that, IPv6 hop-by-hop extension header has to be mandatorily
present?
static_always_inline u8
ip6_tcp_udp_icmp_bad_length (vlib_main_t * vm, vlib_buffer_t * p0)
{
u16 payload_length_host_byte_order;
u32 n_this_buffer, n_bytes_left;
ip6_header_t *ip0 = vlib_buffer_get_current (p0);
u32 headers_size = sizeof (ip0[0]);
u8 *data_this_buffer;
data_this_buffer = (u8 *) (ip0 + 1);
ip6_hop_by_hop_ext_t *ext_hdr = (ip6_hop_by_hop_ext_t *) data_this_buffer;
/* validate really icmp6 next */
if (!(ext_hdr->next_hdr == IP_PROTOCOL_ICMP6)
|| (ext_hdr->next_hdr == IP_PROTOCOL_UDP))
return 0;
::
::
Thanks,
Pankaj Malhotra
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