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samples/bpf: Decrement ttl in fib forwarding example 

Only consider forwarding packets if ttl in received packet is > 1 and
decrement ttl before handing off to bpf_redirect_map.

Signed-off-by: David Ahern <dsahern@gmail.com>
Acked-by: Yonghong Song <yhs@fb.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
This commit is contained in:
David Ahern 2018-05-15 16:20:52 -07:00 committed by Daniel Borkmann
parent 5b26ace650
commit 44edef77bd
1 changed files with 31 additions and 8 deletions
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39
samples/bpf/xdp_fwd_kern.c
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@ -30,12 +30,24 @@ struct bpf_map_def SEC("maps") tx_port = {
.max_entries = 64, .max_entries = 64,
}; };
/* from include/net/ip.h */
static __always_inline int ip_decrease_ttl(struct iphdr *iph)
{
u32 check = (__force u32)iph->check;
check += (__force u32)htons(0x0100);
iph->check = (__force __sum16)(check + (check >= 0xFFFF));
return --iph->ttl;
}
static __always_inline int xdp_fwd_flags(struct xdp_md *ctx, u32 flags) static __always_inline int xdp_fwd_flags(struct xdp_md *ctx, u32 flags)
{ {
void *data_end = (void *)(long)ctx->data_end; void *data_end = (void *)(long)ctx->data_end;
void *data = (void *)(long)ctx->data; void *data = (void *)(long)ctx->data;
struct bpf_fib_lookup fib_params; struct bpf_fib_lookup fib_params;
struct ethhdr *eth = data; struct ethhdr *eth = data;
struct ipv6hdr *ip6h;
struct iphdr *iph;
int out_index; int out_index;
u16 h_proto; u16 h_proto;
u64 nh_off; u64 nh_off;
@ -48,11 +60,14 @@ static __always_inline int xdp_fwd_flags(struct xdp_md *ctx, u32 flags)
h_proto = eth->h_proto; h_proto = eth->h_proto;
if (h_proto == htons(ETH_P_IP)) { if (h_proto == htons(ETH_P_IP)) {
struct iphdr *iph = data + nh_off; iph = data + nh_off;
if (iph + 1 > data_end) if (iph + 1 > data_end)
return XDP_DROP; return XDP_DROP;
if (iph->ttl <= 1)
return XDP_PASS;
fib_params.family = AF_INET; fib_params.family = AF_INET;
fib_params.tos = iph->tos; fib_params.tos = iph->tos;
fib_params.l4_protocol = iph->protocol; fib_params.l4_protocol = iph->protocol;
@ -64,19 +79,22 @@ static __always_inline int xdp_fwd_flags(struct xdp_md *ctx, u32 flags)
} else if (h_proto == htons(ETH_P_IPV6)) { } else if (h_proto == htons(ETH_P_IPV6)) {
struct in6_addr *src = (struct in6_addr *) fib_params.ipv6_src; struct in6_addr *src = (struct in6_addr *) fib_params.ipv6_src;
struct in6_addr *dst = (struct in6_addr *) fib_params.ipv6_dst; struct in6_addr *dst = (struct in6_addr *) fib_params.ipv6_dst;
struct ipv6hdr *iph = data + nh_off;
if (iph + 1 > data_end) ip6h = data + nh_off;
if (ip6h + 1 > data_end)
return XDP_DROP; return XDP_DROP;
if (ip6h->hop_limit <= 1)
return XDP_PASS;
fib_params.family = AF_INET6; fib_params.family = AF_INET6;
fib_params.flowlabel = *(__be32 *)iph & IPV6_FLOWINFO_MASK; fib_params.flowlabel = *(__be32 *)ip6h & IPV6_FLOWINFO_MASK;
fib_params.l4_protocol = iph->nexthdr; fib_params.l4_protocol = ip6h->nexthdr;
fib_params.sport = 0; fib_params.sport = 0;
fib_params.dport = 0; fib_params.dport = 0;
fib_params.tot_len = ntohs(iph->payload_len); fib_params.tot_len = ntohs(ip6h->payload_len);
*src = iph->saddr; *src = ip6h->saddr;
*dst = iph->daddr; *dst = ip6h->daddr;
} else { } else {
return XDP_PASS; return XDP_PASS;
} }
@ -92,6 +110,11 @@ static __always_inline int xdp_fwd_flags(struct xdp_md *ctx, u32 flags)
* forwarding packets are dropped. * forwarding packets are dropped.
*/ */
if (out_index > 0) { if (out_index > 0) {
if (h_proto == htons(ETH_P_IP))
ip_decrease_ttl(iph);
else if (h_proto == htons(ETH_P_IPV6))
ip6h->hop_limit--;
memcpy(eth->h_dest, fib_params.dmac, ETH_ALEN); memcpy(eth->h_dest, fib_params.dmac, ETH_ALEN);
memcpy(eth->h_source, fib_params.smac, ETH_ALEN); memcpy(eth->h_source, fib_params.smac, ETH_ALEN);
return bpf_redirect_map(&tx_port, out_index, 0); return bpf_redirect_map(&tx_port, out_index, 0);