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Commit 44edef77 authored by David Ahern's avatar David Ahern Committed by Daniel Borkmann
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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: default avatarDavid Ahern <dsahern@gmail.com>
Acked-by: default avatarYonghong Song <yhs@fb.com>
Signed-off-by: default avatarDaniel Borkmann <daniel@iogearbox.net>
parent 5b26ace6

samples/bpf/xdp_fwd_kern.c

+31 −8
Original line number Diff line number Diff line
@@ -30,12 +30,24 @@ struct bpf_map_def SEC("maps") tx_port = { 
	.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)

{

	void *data_end = (void *)(long)ctx->data_end;

	void *data = (void *)(long)ctx->data;

	struct bpf_fib_lookup fib_params;

	struct ethhdr *eth = data;

	struct ipv6hdr *ip6h;

	struct iphdr *iph;

	int out_index;

	u16 h_proto;

	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;

	if (h_proto == htons(ETH_P_IP)) {

		struct iphdr *iph = data + nh_off;

		iph = data + nh_off;



		if (iph + 1 > data_end)

			return XDP_DROP;



		if (iph->ttl <= 1)

			return XDP_PASS;



		fib_params.family	= AF_INET;

		fib_params.tos		= iph->tos;

		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)) {

		struct in6_addr *src = (struct in6_addr *) fib_params.ipv6_src;

		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;



		if (ip6h->hop_limit <= 1)

			return XDP_PASS;



		fib_params.family	= AF_INET6;

		fib_params.flowlabel	= *(__be32 *)iph & IPV6_FLOWINFO_MASK;

		fib_params.l4_protocol	= iph->nexthdr;

		fib_params.flowlabel	= *(__be32 *)ip6h & IPV6_FLOWINFO_MASK;

		fib_params.l4_protocol	= ip6h->nexthdr;

		fib_params.sport	= 0;

		fib_params.dport	= 0;

		fib_params.tot_len	= ntohs(iph->payload_len);

		*src			= iph->saddr;

		*dst			= iph->daddr;

		fib_params.tot_len	= ntohs(ip6h->payload_len);

		*src			= ip6h->saddr;

		*dst			= ip6h->daddr;

	} else {

		return XDP_PASS;

	}
@@ -92,6 +110,11 @@ static __always_inline int xdp_fwd_flags(struct xdp_md *ctx, u32 flags) 
	 *       forwarding packets are dropped.

	 */

	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_source, fib_params.smac, ETH_ALEN);

		return bpf_redirect_map(&tx_port, out_index, 0);