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pkt-loop-filter: fix ethernet multicast frame identification

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Multicast, which also includes broadcast, frames can be identified by
looking at the LSB of the first octet of the destination MAC address.

Original-patch-by: Jonathan Toppins <[email protected]>
Signed-off-by: Toke Høiland-Jørgensen <[email protected]>
This commit is contained in:
Toke Høiland-Jørgensen
2022-06-29 16:58:34 +02:00
parent 1b38fda8fb
commit e9aeda404e
1 changed files with 10 additions and 12 deletions
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pkt-loop-filter/pkt-loop-filter.kern.c
+10 -12
View File
@@ -1,4 +1,5 @@
/* SPDX-License-Identifier: GPL-2.0-or-later */
#include <stdbool.h>
#include <linux/bpf.h>
#include <asm/ptrace.h>
#include <bpf/bpf_helpers.h>
@@ -46,16 +47,6 @@ struct {
int active_ifindexes[MAX_IFINDEXES] = {};
unsigned int current_ifindex = 0;
static int ethaddr_equal(__u8 *a, __u8 *b)
{
int i;
for (i = 0; i < ETH_ALEN; i++)
if (a[i] != b[i])
return 0;
return 1;
}
static int get_current_ifindex(void)
{
/* bounds check to placate the verifier */
@@ -65,9 +56,16 @@ static int get_current_ifindex(void)
return active_ifindexes[current_ifindex];
}
/* copy of kernel's version - if the LSB of the first octet is 1 then it is
* a multicast address
*/
static bool is_multicast_ether_addr(const __u8 *addr)
{
return 0x01 & addr[0];
}
static int parse_pkt(struct __sk_buff *skb, struct pkt_loop_key *key)
{
static __u8 mcast_addr[ETH_ALEN] = { 0xff, 0xff, 0xff, 0xff, 0xff, 0xff };
void *data_end = (void *)(unsigned long long)skb->data_end;
void *data = (void *)(unsigned long long)skb->data;
struct hdr_cursor nh = { .pos = data };
@@ -82,7 +80,7 @@ static int parse_pkt(struct __sk_buff *skb, struct pkt_loop_key *key)
__builtin_memcpy(key->src_mac, eth->h_source, ETH_ALEN);
key->src_vlan = skb->vlan_tci;
return ethaddr_equal(eth->h_dest, mcast_addr) ? PKT_TYPE_MULTICAST : PKT_TYPE_UNICAST;
return is_multicast_ether_addr(eth->h_dest) ? PKT_TYPE_MULTICAST : PKT_TYPE_UNICAST;
}
SEC("tc")