Subject: Re: [PATCH bpf-next 7/8] selftests/bpf: Add netlink helper library

From: Stanislav Fomichev <[email-masked]>
Date: Tue, 26 Sep 2023 14:35:18 -0700

On 09/26, Daniel Borkmann wrote:
> Add a basic netlink helper library for the BPF selftests. This has been
> taken and cut down/cleaned up from iproute2. More can be added at some
> later point in time when needed, but for now this covers basics such as
> device creation which we need for BPF selftests / BPF CI.

Should the netlink code be based on ynl
(https://lore.kernel.org/all/[email-masked]/)?
Or it doesn't have full rtnl support yet?

> 
> Signed-off-by: Daniel Borkmann <[email-masked]>
> ---
>  tools/testing/selftests/bpf/Makefile          |  19 +-
>  tools/testing/selftests/bpf/netlink_helpers.c | 358 ++++++++++++++++++
>  tools/testing/selftests/bpf/netlink_helpers.h |  46 +++
>  3 files changed, 418 insertions(+), 5 deletions(-)
>  create mode 100644 tools/testing/selftests/bpf/netlink_helpers.c
>  create mode 100644 tools/testing/selftests/bpf/netlink_helpers.h
> 
> diff --git a/tools/testing/selftests/bpf/Makefile b/tools/testing/selftests/bpf/Makefile
> index 47365161b6fc..b8186ceb31dc 100644
> --- a/tools/testing/selftests/bpf/Makefile
> +++ b/tools/testing/selftests/bpf/Makefile
> @@ -579,11 +579,20 @@ endef
>  # Define test_progs test runner.
>  TRUNNER_TESTS_DIR := prog_tests
>  TRUNNER_BPF_PROGS_DIR := progs
> -TRUNNER_EXTRA_SOURCES := test_progs.c cgroup_helpers.c trace_helpers.c	\
> -			 network_helpers.c testing_helpers.c		\
> -			 btf_helpers.c flow_dissector_load.h		\
> -			 cap_helpers.c test_loader.c xsk.c disasm.c	\
> -			 json_writer.c unpriv_helpers.c 		\
> +TRUNNER_EXTRA_SOURCES := test_progs.c		\
> +			 cgroup_helpers.c	\
> +			 trace_helpers.c	\
> +			 network_helpers.c	\
> +			 testing_helpers.c	\
> +			 btf_helpers.c		\
> +			 cap_helpers.c		\
> +			 unpriv_helpers.c 	\
> +			 netlink_helpers.c	\
> +			 test_loader.c		\
> +			 xsk.c			\
> +			 disasm.c		\
> +			 json_writer.c 		\
> +			 flow_dissector_load.h	\
>  			 ip_check_defrag_frags.h
>  TRUNNER_EXTRA_FILES := $(OUTPUT)/urandom_read $(OUTPUT)/bpf_testmod.ko	\
>  		       $(OUTPUT)/liburandom_read.so			\
> diff --git a/tools/testing/selftests/bpf/netlink_helpers.c b/tools/testing/selftests/bpf/netlink_helpers.c
> new file mode 100644
> index 000000000000..caf36eb1d032
> --- /dev/null
> +++ b/tools/testing/selftests/bpf/netlink_helpers.c
> @@ -0,0 +1,358 @@
> +// SPDX-License-Identifier: GPL-2.0-or-later
> +/* Taken & modified from iproute2's libnetlink.c
> + * Authors: Alexey Kuznetsov, <[email-masked]>
> + */
> +#include <stdio.h>
> +#include <stdlib.h>
> +#include <unistd.h>
> +#include <errno.h>
> +#include <time.h>
> +#include <sys/socket.h>
> +
> +#include "netlink_helpers.h"
> +
> +static int rcvbuf = 1024 * 1024;
> +
> +void rtnl_close(struct rtnl_handle *rth)
> +{
> +	if (rth->fd >= 0) {
> +		close(rth->fd);
> +		rth->fd = -1;
> +	}
> +}
> +
> +int rtnl_open_byproto(struct rtnl_handle *rth, unsigned int subscriptions,
> +		      int protocol)
> +{
> +	socklen_t addr_len;
> +	int sndbuf = 32768;
> +	int one = 1;
> +
> +	memset(rth, 0, sizeof(*rth));
> +	rth->proto = protocol;
> +	rth->fd = socket(AF_NETLINK, SOCK_RAW | SOCK_CLOEXEC, protocol);
> +	if (rth->fd < 0) {
> +		perror("Cannot open netlink socket");
> +		return -1;
> +	}
> +	if (setsockopt(rth->fd, SOL_SOCKET, SO_SNDBUF,
> +		       &sndbuf, sizeof(sndbuf)) < 0) {
> +		perror("SO_SNDBUF");
> +		goto err;
> +	}
> +	if (setsockopt(rth->fd, SOL_SOCKET, SO_RCVBUF,
> +		       &rcvbuf, sizeof(rcvbuf)) < 0) {
> +		perror("SO_RCVBUF");
> +		goto err;
> +	}
> +
> +	/* Older kernels may no support extended ACK reporting */
> +	setsockopt(rth->fd, SOL_NETLINK, NETLINK_EXT_ACK,
> +		   &one, sizeof(one));
> +
> +	memset(&rth->local, 0, sizeof(rth->local));
> +	rth->local.nl_family = AF_NETLINK;
> +	rth->local.nl_groups = subscriptions;
> +
> +	if (bind(rth->fd, (struct sockaddr *)&rth->local,
> +		 sizeof(rth->local)) < 0) {
> +		perror("Cannot bind netlink socket");
> +		goto err;
> +	}
> +	addr_len = sizeof(rth->local);
> +	if (getsockname(rth->fd, (struct sockaddr *)&rth->local,
> +			&addr_len) < 0) {
> +		perror("Cannot getsockname");
> +		goto err;
> +	}
> +	if (addr_len != sizeof(rth->local)) {
> +		fprintf(stderr, "Wrong address length %d\n", addr_len);
> +		goto err;
> +	}
> +	if (rth->local.nl_family != AF_NETLINK) {
> +		fprintf(stderr, "Wrong address family %d\n",
> +			rth->local.nl_family);
> +		goto err;
> +	}
> +	rth->seq = time(NULL);
> +	return 0;
> +err:
> +	rtnl_close(rth);
> +	return -1;
> +}
> +
> +int rtnl_open(struct rtnl_handle *rth, unsigned int subscriptions)
> +{
> +	return rtnl_open_byproto(rth, subscriptions, NETLINK_ROUTE);
> +}
> +
> +static int __rtnl_recvmsg(int fd, struct msghdr *msg, int flags)
> +{
> +	int len;
> +
> +	do {
> +		len = recvmsg(fd, msg, flags);
> +	} while (len < 0 && (errno == EINTR || errno == EAGAIN));
> +	if (len < 0) {
> +		fprintf(stderr, "netlink receive error %s (%d)\n",
> +			strerror(errno), errno);
> +		return -errno;
> +	}
> +	if (len == 0) {
> +		fprintf(stderr, "EOF on netlink\n");
> +		return -ENODATA;
> +	}
> +	return len;
> +}
> +
> +static int rtnl_recvmsg(int fd, struct msghdr *msg, char **answer)
> +{
> +	struct iovec *iov = msg->msg_iov;
> +	char *buf;
> +	int len;
> +
> +	iov->iov_base = NULL;
> +	iov->iov_len = 0;
> +
> +	len = __rtnl_recvmsg(fd, msg, MSG_PEEK | MSG_TRUNC);
> +	if (len < 0)
> +		return len;
> +	if (len < 32768)
> +		len = 32768;
> +	buf = malloc(len);
> +	if (!buf) {
> +		fprintf(stderr, "malloc error: not enough buffer\n");
> +		return -ENOMEM;
> +	}
> +	iov->iov_base = buf;
> +	iov->iov_len = len;
> +	len = __rtnl_recvmsg(fd, msg, 0);
> +	if (len < 0) {
> +		free(buf);
> +		return len;
> +	}
> +	if (answer)
> +		*answer = buf;
> +	else
> +		free(buf);
> +	return len;
> +}
> +
> +static void rtnl_talk_error(struct nlmsghdr *h, struct nlmsgerr *err,
> +			    nl_ext_ack_fn_t errfn)
> +{
> +	fprintf(stderr, "RTNETLINK answers: %s\n",
> +		strerror(-err->error));
> +}
> +
> +static int __rtnl_talk_iov(struct rtnl_handle *rtnl, struct iovec *iov,
> +			   size_t iovlen, struct nlmsghdr **answer,
> +			   bool show_rtnl_err, nl_ext_ack_fn_t errfn)
> +{
> +	struct sockaddr_nl nladdr = { .nl_family = AF_NETLINK };
> +	struct iovec riov;
> +	struct msghdr msg = {
> +		.msg_name	= &nladdr,
> +		.msg_namelen	= sizeof(nladdr),
> +		.msg_iov	= iov,
> +		.msg_iovlen	= iovlen,
> +	};
> +	unsigned int seq = 0;
> +	struct nlmsghdr *h;
> +	int i, status;
> +	char *buf;
> +
> +	for (i = 0; i < iovlen; i++) {
> +		h = iov[i].iov_base;
> +		h->nlmsg_seq = seq = ++rtnl->seq;
> +		if (answer == NULL)
> +			h->nlmsg_flags |= NLM_F_ACK;
> +	}
> +	status = sendmsg(rtnl->fd, &msg, 0);
> +	if (status < 0) {
> +		perror("Cannot talk to rtnetlink");
> +		return -1;
> +	}
> +	/* change msg to use the response iov */
> +	msg.msg_iov = &riov;
> +	msg.msg_iovlen = 1;
> +	i = 0;
> +	while (1) {
> +next:
> +		status = rtnl_recvmsg(rtnl->fd, &msg, &buf);
> +		++i;
> +		if (status < 0)
> +			return status;
> +		if (msg.msg_namelen != sizeof(nladdr)) {
> +			fprintf(stderr,
> +				"Sender address length == %d!\n",
> +				msg.msg_namelen);
> +			exit(1);
> +		}
> +		for (h = (struct nlmsghdr *)buf; status >= sizeof(*h); ) {
> +			int len = h->nlmsg_len;
> +			int l = len - sizeof(*h);
> +
> +			if (l < 0 || len > status) {
> +				if (msg.msg_flags & MSG_TRUNC) {
> +					fprintf(stderr, "Truncated message!\n");
> +					free(buf);
> +					return -1;
> +				}
> +				fprintf(stderr,
> +					"Malformed message: len=%d!\n",
> +					len);
> +				exit(1);
> +			}
> +			if (nladdr.nl_pid != 0 ||
> +			    h->nlmsg_pid != rtnl->local.nl_pid ||
> +			    h->nlmsg_seq > seq || h->nlmsg_seq < seq - iovlen) {
> +				/* Don't forget to skip that message. */
> +				status -= NLMSG_ALIGN(len);
> +				h = (struct nlmsghdr *)((char *)h + NLMSG_ALIGN(len));
> +				continue;
> +			}
> +			if (h->nlmsg_type == NLMSG_ERROR) {
> +				struct nlmsgerr *err = (struct nlmsgerr *)NLMSG_DATA(h);
> +				int error = err->error;
> +
> +				if (l < sizeof(struct nlmsgerr)) {
> +					fprintf(stderr, "ERROR truncated\n");
> +					free(buf);
> +					return -1;
> +				}
> +				if (error) {
> +					errno = -error;
> +					if (rtnl->proto != NETLINK_SOCK_DIAG &&
> +					    show_rtnl_err)
> +						rtnl_talk_error(h, err, errfn);
> +				}
> +				if (i < iovlen) {
> +					free(buf);
> +					goto next;
> +				}
> +				if (error) {
> +					free(buf);
> +					return -i;
> +				}
> +				if (answer)
> +					*answer = (struct nlmsghdr *)buf;
> +				else
> +					free(buf);
> +				return 0;
> +			}
> +			if (answer) {
> +				*answer = (struct nlmsghdr *)buf;
> +				return 0;
> +			}
> +			fprintf(stderr, "Unexpected reply!\n");
> +			status -= NLMSG_ALIGN(len);
> +			h = (struct nlmsghdr *)((char *)h + NLMSG_ALIGN(len));
> +		}
> +		free(buf);
> +		if (msg.msg_flags & MSG_TRUNC) {
> +			fprintf(stderr, "Message truncated!\n");
> +			continue;
> +		}
> +		if (status) {
> +			fprintf(stderr, "Remnant of size %d!\n", status);
> +			exit(1);
> +		}
> +	}
> +}
> +
> +static int __rtnl_talk(struct rtnl_handle *rtnl, struct nlmsghdr *n,
> +		       struct nlmsghdr **answer, bool show_rtnl_err,
> +		       nl_ext_ack_fn_t errfn)
> +{
> +	struct iovec iov = {
> +		.iov_base	= n,
> +		.iov_len	= n->nlmsg_len,
> +	};
> +
> +	return __rtnl_talk_iov(rtnl, &iov, 1, answer, show_rtnl_err, errfn);
> +}
> +
> +int rtnl_talk(struct rtnl_handle *rtnl, struct nlmsghdr *n,
> +	      struct nlmsghdr **answer)
> +{
> +	return __rtnl_talk(rtnl, n, answer, true, NULL);
> +}
> +
> +int addattr(struct nlmsghdr *n, int maxlen, int type)
> +{
> +	return addattr_l(n, maxlen, type, NULL, 0);
> +}
> +
> +int addattr8(struct nlmsghdr *n, int maxlen, int type, __u8 data)
> +{
> +	return addattr_l(n, maxlen, type, &data, sizeof(__u8));
> +}
> +
> +int addattr16(struct nlmsghdr *n, int maxlen, int type, __u16 data)
> +{
> +	return addattr_l(n, maxlen, type, &data, sizeof(__u16));
> +}
> +
> +int addattr32(struct nlmsghdr *n, int maxlen, int type, __u32 data)
> +{
> +	return addattr_l(n, maxlen, type, &data, sizeof(__u32));
> +}
> +
> +int addattr64(struct nlmsghdr *n, int maxlen, int type, __u64 data)
> +{
> +	return addattr_l(n, maxlen, type, &data, sizeof(__u64));
> +}
> +
> +int addattrstrz(struct nlmsghdr *n, int maxlen, int type, const char *str)
> +{
> +	return addattr_l(n, maxlen, type, str, strlen(str)+1);
> +}
> +
> +int addattr_l(struct nlmsghdr *n, int maxlen, int type, const void *data,
> +	      int alen)
> +{
> +	int len = RTA_LENGTH(alen);
> +	struct rtattr *rta;
> +
> +	if (NLMSG_ALIGN(n->nlmsg_len) + RTA_ALIGN(len) > maxlen) {
> +		fprintf(stderr, "%s: Message exceeded bound of %d\n",
> +			__func__, maxlen);
> +		return -1;
> +	}
> +	rta = NLMSG_TAIL(n);
> +	rta->rta_type = type;
> +	rta->rta_len = len;
> +	if (alen)
> +		memcpy(RTA_DATA(rta), data, alen);
> +	n->nlmsg_len = NLMSG_ALIGN(n->nlmsg_len) + RTA_ALIGN(len);
> +	return 0;
> +}
> +
> +int addraw_l(struct nlmsghdr *n, int maxlen, const void *data, int len)
> +{
> +	if (NLMSG_ALIGN(n->nlmsg_len) + NLMSG_ALIGN(len) > maxlen) {
> +		fprintf(stderr, "%s: Message exceeded bound of %d\n",
> +			__func__, maxlen);
> +		return -1;
> +	}
> +
> +	memcpy(NLMSG_TAIL(n), data, len);
> +	memset((void *) NLMSG_TAIL(n) + len, 0, NLMSG_ALIGN(len) - len);
> +	n->nlmsg_len = NLMSG_ALIGN(n->nlmsg_len) + NLMSG_ALIGN(len);
> +	return 0;
> +}
> +
> +struct rtattr *addattr_nest(struct nlmsghdr *n, int maxlen, int type)
> +{
> +	struct rtattr *nest = NLMSG_TAIL(n);
> +
> +	addattr_l(n, maxlen, type, NULL, 0);
> +	return nest;
> +}
> +
> +int addattr_nest_end(struct nlmsghdr *n, struct rtattr *nest)
> +{
> +	nest->rta_len = (void *)NLMSG_TAIL(n) - (void *)nest;
> +	return n->nlmsg_len;
> +}
> diff --git a/tools/testing/selftests/bpf/netlink_helpers.h b/tools/testing/selftests/bpf/netlink_helpers.h
> new file mode 100644
> index 000000000000..68116818a47e
> --- /dev/null
> +++ b/tools/testing/selftests/bpf/netlink_helpers.h
> @@ -0,0 +1,46 @@
> +/* SPDX-License-Identifier: GPL-2.0-or-later */
> +#ifndef NETLINK_HELPERS_H
> +#define NETLINK_HELPERS_H
> +
> +#include <string.h>
> +#include <linux/netlink.h>
> +#include <linux/rtnetlink.h>
> +
> +struct rtnl_handle {
> +	int			fd;
> +	struct sockaddr_nl	local;
> +	struct sockaddr_nl	peer;
> +	__u32			seq;
> +	__u32			dump;
> +	int			proto;
> +	FILE			*dump_fp;
> +#define RTNL_HANDLE_F_LISTEN_ALL_NSID		0x01
> +#define RTNL_HANDLE_F_SUPPRESS_NLERR		0x02
> +#define RTNL_HANDLE_F_STRICT_CHK		0x04
> +	int			flags;
> +};
> +
> +#define NLMSG_TAIL(nmsg) \
> +	((struct rtattr *) (((void *) (nmsg)) + NLMSG_ALIGN((nmsg)->nlmsg_len)))
> +
> +typedef int (*nl_ext_ack_fn_t)(const char *errmsg, uint32_t off,
> +			       const struct nlmsghdr *inner_nlh);
> +
> +int rtnl_open(struct rtnl_handle *rth, unsigned int subscriptions)
> +	      __attribute__((warn_unused_result));
> +void rtnl_close(struct rtnl_handle *rth);
> +int rtnl_talk(struct rtnl_handle *rtnl, struct nlmsghdr *n,
> +	      struct nlmsghdr **answer)
> +	      __attribute__((warn_unused_result));
> +
> +int addattr(struct nlmsghdr *n, int maxlen, int type);
> +int addattr8(struct nlmsghdr *n, int maxlen, int type, __u8 data);
> +int addattr16(struct nlmsghdr *n, int maxlen, int type, __u16 data);
> +int addattr32(struct nlmsghdr *n, int maxlen, int type, __u32 data);
> +int addattr64(struct nlmsghdr *n, int maxlen, int type, __u64 data);
> +int addattrstrz(struct nlmsghdr *n, int maxlen, int type, const char *data);
> +int addattr_l(struct nlmsghdr *n, int maxlen, int type, const void *data, int alen);
> +int addraw_l(struct nlmsghdr *n, int maxlen, const void *data, int len);
> +struct rtattr *addattr_nest(struct nlmsghdr *n, int maxlen, int type);
> +int addattr_nest_end(struct nlmsghdr *n, struct rtattr *nest);
> +#endif /* NETLINK_HELPERS_H */
> -- 
> 2.34.1
>