lib/namespace.c

/* SPDX-License-Identifier: GPL-2.0-or-later */
/*
 * namespace.c
 */

#include <sys/statvfs.h>
#include <fcntl.h>
#include <dirent.h>
#include <limits.h>
#include <linux/net_namespace.h>

#include "utils.h"
#include "namespace.h"
#include "libnetlink.h"

static void bind_etc(const char *name)
{
	char etc_netns_path[sizeof(NETNS_ETC_DIR) + NAME_MAX];
	char netns_name[PATH_MAX];
	char etc_name[PATH_MAX];
	struct dirent *entry;
	DIR *dir;

	if (strlen(name) >= NAME_MAX)
		return;

	snprintf(etc_netns_path, sizeof(etc_netns_path), "%s/%s", NETNS_ETC_DIR, name);
	dir = opendir(etc_netns_path);
	if (!dir)
		return;

	while ((entry = readdir(dir)) != NULL) {
		if (strcmp(entry->d_name, ".") == 0)
			continue;
		if (strcmp(entry->d_name, "..") == 0)
			continue;
		snprintf(netns_name, sizeof(netns_name), "%s/%s", etc_netns_path, entry->d_name);
		snprintf(etc_name, sizeof(etc_name), "/etc/%s", entry->d_name);
		if (mount(netns_name, etc_name, "none", MS_BIND, NULL) < 0) {
			fprintf(stderr, "Bind %s -> %s failed: %s\n",
				netns_name, etc_name, strerror(errno));
		}
	}
	closedir(dir);
}

int netns_switch(char *name)
{
	char net_path[PATH_MAX];
	int netns;
	unsigned long mountflags = 0;
	struct statvfs fsstat;

	snprintf(net_path, sizeof(net_path), "%s/%s", NETNS_RUN_DIR, name);
	netns = open(net_path, O_RDONLY | O_CLOEXEC);
	if (netns < 0) {
		fprintf(stderr, "Cannot open network namespace \"%s\": %s\n",
			name, strerror(errno));
		return -1;
	}

	if (setns(netns, CLONE_NEWNET) < 0) {
		fprintf(stderr, "setting the network namespace \"%s\" failed: %s\n",
			name, strerror(errno));
		close(netns);
		return -1;
	}
	close(netns);

	if (unshare(CLONE_NEWNS) < 0) {
		fprintf(stderr, "unshare failed: %s\n", strerror(errno));
		return -1;
	}
	/* Don't let any mounts propagate back to the parent */
	if (mount("", "/", "none", MS_SLAVE | MS_REC, NULL)) {
		fprintf(stderr, "\"mount --make-rslave /\" failed: %s\n",
			strerror(errno));
		return -1;
	}

	/* Mount a version of /sys that describes the network namespace */

	if (umount2("/sys", MNT_DETACH) < 0) {
		/* If this fails, perhaps there wasn't a sysfs instance mounted. Good. */
		if (statvfs("/sys", &fsstat) == 0) {
			/* We couldn't umount the sysfs, we'll attempt to overlay it.
			 * A read-only instance can't be shadowed with a read-write one. */
			if (fsstat.f_flag & ST_RDONLY)
				mountflags = MS_RDONLY;
		}
	}
	if (mount(name, "/sys", "sysfs", mountflags, NULL) < 0) {
		fprintf(stderr, "mount of /sys failed: %s\n",strerror(errno));
		return -1;
	}

	/* Setup bind mounts for config files in /etc */
	bind_etc(name);
	return 0;
}

int netns_get_fd(const char *name)
{
	char pathbuf[PATH_MAX];
	const char *path, *ptr;

	path = name;
	ptr = strchr(name, '/');
	if (!ptr) {
		snprintf(pathbuf, sizeof(pathbuf), "%s/%s",
			NETNS_RUN_DIR, name );
		path = pathbuf;
	}
	return open(path, O_RDONLY);
}

int netns_foreach(int (*func)(char *nsname, void *arg), void *arg)
{
	DIR *dir;
	struct dirent *entry;

	dir = opendir(NETNS_RUN_DIR);
	if (!dir) {
		if (errno == ENOENT)
			return 0;

		fprintf(stderr, "Failed to open directory %s: %s\n",
			NETNS_RUN_DIR, strerror(errno));
		return -1;
	}

	while ((entry = readdir(dir)) != NULL) {
		if (strcmp(entry->d_name, ".") == 0)
			continue;
		if (strcmp(entry->d_name, "..") == 0)
			continue;
		if (func(entry->d_name, arg))
			break;
	}

	closedir(dir);
	return 0;
}

int netns_id_from_name(struct rtnl_handle *rtnl, const char *name)
{
	struct {
		struct nlmsghdr n;
		struct rtgenmsg g;
		char            buf[1024];
	} req = {
		.n.nlmsg_len = NLMSG_LENGTH(sizeof(struct rtgenmsg)),
		.n.nlmsg_flags = NLM_F_REQUEST,
		.n.nlmsg_type = RTM_GETNSID,
		.g.rtgen_family = AF_UNSPEC,
	};
	struct nlmsghdr *answer;
	struct rtattr *tb[NETNSA_MAX + 1];
	struct rtgenmsg *rthdr;
	int len, fd, ret = -1;

	fd = netns_get_fd(name);
	if (fd < 0)
		return fd;

	addattr32(&req.n, 1024, NETNSA_FD, fd);
	if (rtnl_talk(rtnl, &req.n, &answer) < 0) {
		close(fd);
		return -2;
	}
	close(fd);

	/* Validate message and parse attributes */
	if (answer->nlmsg_type == NLMSG_ERROR)
		goto out;

	rthdr = NLMSG_DATA(answer);
	len = answer->nlmsg_len - NLMSG_SPACE(sizeof(*rthdr));
	if (len < 0)
		goto out;

	parse_rtattr(tb, NETNSA_MAX, NETNS_RTA(rthdr), len);

	if (tb[NETNSA_NSID])
		ret = rta_getattr_s32(tb[NETNSA_NSID]);

out:
	free(answer);
	return ret;
}

struct netns_name_from_id_ctx {
	int32_t id;
	char *name;
	struct rtnl_handle *rth;
};

static int netns_name_from_id_func(char *nsname, void *arg)
{
	struct netns_name_from_id_ctx *ctx = arg;
	int32_t ret;

	ret = netns_id_from_name(ctx->rth, nsname);
	if (ret < 0 || ret != ctx->id)
		return 0;
	ctx->name = strdup(nsname);
	return 1;
}

char *netns_name_from_id(int32_t id)
{
	struct rtnl_handle rth;
	struct netns_name_from_id_ctx ctx = {
		.id = id,
		.rth = &rth,
	};

	if (rtnl_open(&rth, 0) < 0)
		return NULL;
	netns_foreach(netns_name_from_id_func, &ctx);
	rtnl_close(&rth);

	return ctx.name;
}