Re: [PATCH bpf 2/2] selftests/net: test sk_filter support for SKF_NET_OFF on frags

[Stanislav Fomichev <stfomichev@gmail.com>]

On 04/03, Willem de Bruijn wrote:
> From: Willem de Bruijn <willemb@google.com>
> 
> Verify that a classic BPF linux socket filter correctly matches
> packet contents. Including when accessing contents in an
> skb_frag.
> 
> 1. Open a SOCK_RAW socket with a classic BPF filter on UDP dport 8000.
> 2. Open a tap device with IFF_NAPI_FRAGS to inject skbs with frags.
> 3. Send a packet for which the UDP header is in frag[0].
> 4. Receive this packet to demonstrate that the socket accepted it.
> 
> Signed-off-by: Willem de Bruijn <willemb@google.com>

Acked-by: Stanislav Fomichev <sdf@fomichev.me>

My (weak) preference is to put (most) bpf-related things under
selftests/bpf, but since you already have it working, not sure
it's worth the effort.

> ---
>  tools/testing/selftests/net/.gitignore     |   1 +
>  tools/testing/selftests/net/Makefile       |   2 +
>  tools/testing/selftests/net/skf_net_off.c  | 244 +++++++++++++++++++++
>  tools/testing/selftests/net/skf_net_off.sh |  28 +++
>  4 files changed, 275 insertions(+)
>  create mode 100644 tools/testing/selftests/net/skf_net_off.c
>  create mode 100755 tools/testing/selftests/net/skf_net_off.sh
> 
> diff --git a/tools/testing/selftests/net/.gitignore b/tools/testing/selftests/net/.gitignore
> index 679542f565a4..532bb732bc6d 100644
> --- a/tools/testing/selftests/net/.gitignore
> +++ b/tools/testing/selftests/net/.gitignore
> @@ -39,6 +39,7 @@ scm_rights
>  sk_bind_sendto_listen
>  sk_connect_zero_addr
>  sk_so_peek_off
> +skf_net_off
>  socket
>  so_incoming_cpu
>  so_netns_cookie
> diff --git a/tools/testing/selftests/net/Makefile b/tools/testing/selftests/net/Makefile
> index 6d718b478ed8..124078b56fa4 100644
> --- a/tools/testing/selftests/net/Makefile
> +++ b/tools/testing/selftests/net/Makefile
> @@ -106,6 +106,8 @@ TEST_PROGS += ipv6_route_update_soft_lockup.sh
>  TEST_PROGS += busy_poll_test.sh
>  TEST_GEN_PROGS += proc_net_pktgen
>  TEST_PROGS += lwt_dst_cache_ref_loop.sh
> +TEST_PROGS += skf_net_off.sh
> +TEST_GEN_FILES += skf_net_off
>  
>  # YNL files, must be before "include ..lib.mk"
>  YNL_GEN_FILES := busy_poller netlink-dumps
> diff --git a/tools/testing/selftests/net/skf_net_off.c b/tools/testing/selftests/net/skf_net_off.c
> new file mode 100644
> index 000000000000..1fdf61d6cd7f
> --- /dev/null
> +++ b/tools/testing/selftests/net/skf_net_off.c
> @@ -0,0 +1,244 @@
> +// SPDX-License-Identifier: GPL-2.0
> +
> +/* Open a tun device.
> + *
> + * [modifications: use IFF_NAPI_FRAGS, add sk filter]
> + *
> + * Expects the device to have been configured previously, e.g.:
> + *   sudo ip tuntap add name tap1 mode tap
> + *   sudo ip link set tap1 up
> + *   sudo ip link set dev tap1 addr 02:00:00:00:00:01
> + *   sudo ip -6 addr add fdab::1 peer fdab::2 dev tap1 nodad
> + *
> + * And to avoid premature pskb_may_pull:
> + *
> + *   sudo ethtool -K tap1 gro off
> + *   sudo bash -c 'echo 0 > /proc/sys/net/ipv4/ip_early_demux'
> + */
> +
> +#define _GNU_SOURCE
> +
> +#include <arpa/inet.h>
> +#include <errno.h>
> +#include <error.h>
> +#include <fcntl.h>
> +#include <getopt.h>
> +#include <linux/filter.h>
> +#include <linux/if.h>
> +#include <linux/if_packet.h>
> +#include <linux/if_tun.h>
> +#include <linux/ipv6.h>
> +#include <netinet/if_ether.h>
> +#include <netinet/in.h>
> +#include <netinet/ip.h>
> +#include <netinet/ip6.h>
> +#include <netinet/udp.h>
> +#include <poll.h>
> +#include <signal.h>
> +#include <stdbool.h>
> +#include <stddef.h>
> +#include <stdio.h>
> +#include <stdlib.h>
> +#include <string.h>
> +#include <sys/ioctl.h>
> +#include <sys/socket.h>
> +#include <sys/poll.h>
> +#include <sys/types.h>
> +#include <sys/uio.h>
> +#include <unistd.h>
> +
> +static bool cfg_do_filter;
> +static bool cfg_do_frags;
> +static int cfg_dst_port = 8000;
> +static char *cfg_ifname;
> +
> +static int tun_open(const char *tun_name)
> +{
> +	struct ifreq ifr = {0};
> +	int fd, ret;
> +
> +	fd = open("/dev/net/tun", O_RDWR);
> +	if (fd == -1)
> +		error(1, errno, "open /dev/net/tun");
> +
> +	ifr.ifr_flags = IFF_TAP;
> +	if (cfg_do_frags)
> +		ifr.ifr_flags |= IFF_NAPI | IFF_NAPI_FRAGS;
> +
> +	strncpy(ifr.ifr_name, tun_name, IFNAMSIZ - 1);
> +
> +	ret = ioctl(fd, TUNSETIFF, &ifr);
> +	if (ret)
> +		error(1, ret, "ioctl TUNSETIFF");
> +
> +	return fd;
> +}
> +
> +static void sk_set_filter(int fd)
> +{
> +	const int offset_proto = offsetof(struct ip6_hdr, ip6_nxt);
> +	const int offset_dport = sizeof(struct ip6_hdr) + offsetof(struct udphdr, dest);
> +
> +	/* Filter UDP packets with destination port cfg_dst_port */
> +	struct sock_filter filter_code[] = {
> +		BPF_STMT(BPF_LD  + BPF_B   + BPF_ABS, SKF_AD_OFF + SKF_AD_PKTTYPE),
> +		BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, PACKET_HOST, 0, 4),
> +		BPF_STMT(BPF_LD  + BPF_B   + BPF_ABS, SKF_NET_OFF + offset_proto),
> +		BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, IPPROTO_UDP, 0, 2),
> +		BPF_STMT(BPF_LD  + BPF_H   + BPF_ABS, SKF_NET_OFF + offset_dport),
> +		BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, cfg_dst_port, 1, 0),
> +		BPF_STMT(BPF_RET + BPF_K, 0),
> +		BPF_STMT(BPF_RET + BPF_K, 0xFFFF),
> +	};
> +
> +	struct sock_fprog filter = {
> +		sizeof(filter_code) / sizeof(filter_code[0]),
> +		filter_code,
> +	};
> +
> +	if (setsockopt(fd, SOL_SOCKET, SO_ATTACH_FILTER, &filter, sizeof(filter)))
> +		error(1, errno, "setsockopt attach filter");
> +}
> +
> +static int raw_open(void)
> +{
> +	int fd;
> +
> +	fd = socket(PF_INET6, SOCK_RAW, IPPROTO_UDP);
> +	if (fd == -1)
> +		error(1, errno, "socket raw (udp)");
> +
> +	if (cfg_do_filter)
> +		sk_set_filter(fd);
> +
> +	return fd;
> +}
> +
> +static void tun_write(int fd)
> +{
> +	const char eth_src[] = { 0x02, 0x00, 0x00, 0x00, 0x00, 0x02 };
> +	const char eth_dst[] = { 0x02, 0x00, 0x00, 0x00, 0x00, 0x01 };
> +	struct tun_pi pi = {0};
> +	struct ipv6hdr ip6h = {0};
> +	struct udphdr uh = {0};
> +	struct ethhdr eth = {0};
> +	uint32_t payload;
> +	struct iovec iov[5];
> +	int ret;
> +
> +	pi.proto = htons(ETH_P_IPV6);
> +
> +	memcpy(eth.h_source, eth_src, sizeof(eth_src));
> +	memcpy(eth.h_dest, eth_dst, sizeof(eth_dst));
> +	eth.h_proto = htons(ETH_P_IPV6);
> +
> +	ip6h.version = 6;
> +	ip6h.payload_len = htons(sizeof(uh) + sizeof(uint32_t));
> +	ip6h.nexthdr = IPPROTO_UDP;
> +	ip6h.hop_limit = 8;
> +	if (inet_pton(AF_INET6, "fdab::2", &ip6h.saddr) != 1)
> +		error(1, errno, "inet_pton src");
> +	if (inet_pton(AF_INET6, "fdab::1", &ip6h.daddr) != 1)
> +		error(1, errno, "inet_pton src");
> +
> +	uh.source = htons(8000);
> +	uh.dest = htons(cfg_dst_port);
> +	uh.len = ip6h.payload_len;
> +	uh.check = 0;
> +
> +	payload = htonl(0xABABABAB);		/* Covered in IPv6 length */
> +
> +	iov[0].iov_base = &pi;
> +	iov[0].iov_len  = sizeof(pi);
> +	iov[1].iov_base = &eth;
> +	iov[1].iov_len  = sizeof(eth);
> +	iov[2].iov_base = &ip6h;
> +	iov[2].iov_len  = sizeof(ip6h);
> +	iov[3].iov_base = &uh;
> +	iov[3].iov_len  = sizeof(uh);
> +	iov[4].iov_base = &payload;
> +	iov[4].iov_len  = sizeof(payload);
> +
> +	ret = writev(fd, iov, sizeof(iov) / sizeof(iov[0]));
> +	if (ret <= 0)
> +		error(1, errno, "writev");
> +}
> +
> +static void raw_read(int fd)
> +{
> +	struct timeval tv = { .tv_usec = 100 * 1000 };
> +	struct msghdr msg = {0};
> +	struct iovec iov[2];
> +	struct udphdr uh;
> +	uint32_t payload[2];
> +	int ret;
> +
> +	if (setsockopt(fd, SOL_SOCKET, SO_RCVTIMEO, &tv, sizeof(tv)))
> +		error(1, errno, "setsockopt rcvtimeo udp");
> +
> +	iov[0].iov_base = &uh;
> +	iov[0].iov_len = sizeof(uh);
> +
> +	iov[1].iov_base = payload;
> +	iov[1].iov_len = sizeof(payload);
> +
> +	msg.msg_iov = iov;
> +	msg.msg_iovlen = sizeof(iov) / sizeof(iov[0]);
> +
> +	ret = recvmsg(fd, &msg, 0);
> +	if (ret <= 0)
> +		error(1, errno, "read raw");
> +	if (ret != sizeof(uh) + sizeof(payload[0]))
> +		error(1, errno, "read raw: len=%d\n", ret);
> +
> +	fprintf(stderr, "raw recv: 0x%x\n", payload[0]);
> +}
> +
> +static void parse_opts(int argc, char **argv)
> +{
> +	int c;
> +
> +	while ((c = getopt(argc, argv, "fFi:")) != -1) {
> +		switch (c) {
> +		case 'f':
> +			cfg_do_filter = true;
> +			printf("bpf filter enabled\n");
> +			break;
> +		case 'F':
> +			cfg_do_frags = true;
> +			printf("napi frags mode enabled\n");
> +			break;
> +		case 'i':
> +			cfg_ifname = optarg;
> +			break;
> +		default:
> +			error(1, 0, "unknown option %c", optopt);
> +			break;
> +		}
> +	}
> +
> +	if (!cfg_ifname)
> +		error(1, 0, "must specify tap interface name (-i)");
> +}
> +
> +int main(int argc, char **argv)
> +{
> +	int fdt, fdr;
> +
> +	parse_opts(argc, argv);
> +
> +	fdr = raw_open();
> +	fdt = tun_open(cfg_ifname);
> +
> +	tun_write(fdt);
> +	raw_read(fdr);
> +
> +	if (close(fdt))
> +		error(1, errno, "close tun");
> +	if (close(fdr))
> +		error(1, errno, "close udp");
> +
> +	fprintf(stderr, "OK\n");
> +	return 0;
> +}
> +
> diff --git a/tools/testing/selftests/net/skf_net_off.sh b/tools/testing/selftests/net/skf_net_off.sh
> new file mode 100755
> index 000000000000..e9cce93a0258
> --- /dev/null
> +++ b/tools/testing/selftests/net/skf_net_off.sh
> @@ -0,0 +1,28 @@
> +#!/bin/bash
> +# SPDX-License-Identifier: GPL-2.0
> +
> +readonly NS="ns-$(mktemp -u XXXXXX)"
> +
> +cleanup() {
> +	ip netns del $NS
> +}
> +
> +ip netns add $NS
> +trap cleanup EXIT
> +
> +ip -netns $NS link set lo up
> +ip -netns $NS tuntap add name tap1 mode tap
> +ip -netns $NS link set tap1 up
> +ip -netns $NS link set dev tap1 addr 02:00:00:00:00:01
> +ip -netns $NS -6 addr add fdab::1 peer fdab::2 dev tap1 nodad
> +ip netns exec $NS ethtool -K tap1 gro off
> +ip netns exec $NS sysctl -w net.ipv4.ip_early_demux=0

Curious: why disable ip_early_demux here?