path: root/src/nspawn/nspawn-network.c

/* SPDX-License-Identifier: LGPL-2.1-or-later */

#include <net/if.h>
#include <linux/if.h>
#include <linux/veth.h>
#include <sys/file.h>

#include "sd-device.h"
#include "sd-id128.h"
#include "sd-netlink.h"

#include "alloc-util.h"
#include "ether-addr-util.h"
#include "hexdecoct.h"
#include "lockfile-util.h"
#include "missing_network.h"
#include "netif-naming-scheme.h"
#include "netlink-util.h"
#include "nspawn-network.h"
#include "parse-util.h"
#include "siphash24.h"
#include "socket-netlink.h"
#include "socket-util.h"
#include "stat-util.h"
#include "string-util.h"
#include "strv.h"
#include "udev-util.h"
#include "util.h"

#define HOST_HASH_KEY SD_ID128_MAKE(1a,37,6f,c7,46,ec,45,0b,ad,a3,d5,31,06,60,5d,b1)
#define CONTAINER_HASH_KEY SD_ID128_MAKE(c3,c4,f9,19,b5,57,b2,1c,e6,cf,14,27,03,9c,ee,a2)
#define VETH_EXTRA_HOST_HASH_KEY SD_ID128_MAKE(48,c7,f6,b7,ea,9d,4c,9e,b7,28,d4,de,91,d5,bf,66)
#define VETH_EXTRA_CONTAINER_HASH_KEY SD_ID128_MAKE(af,50,17,61,ce,f9,4d,35,84,0d,2b,20,54,be,ce,59)
#define MACVLAN_HASH_KEY SD_ID128_MAKE(00,13,6d,bc,66,83,44,81,bb,0c,f9,51,1f,24,a6,6f)
#define SHORTEN_IFNAME_HASH_KEY SD_ID128_MAKE(e1,90,a4,04,a8,ef,4b,51,8c,cc,c3,3a,9f,11,fc,a2)

static int remove_one_link(sd_netlink *rtnl, const char *name) {
        _cleanup_(sd_netlink_message_unrefp) sd_netlink_message *m = NULL;
        int r;

        if (isempty(name))
                return 0;

        r = sd_rtnl_message_new_link(rtnl, &m, RTM_DELLINK, 0);
        if (r < 0)
                return log_error_errno(r, "Failed to allocate netlink message: %m");

        r = sd_netlink_message_append_string(m, IFLA_IFNAME, name);
        if (r < 0)
                return log_error_errno(r, "Failed to add netlink interface name: %m");

        r = sd_netlink_call(rtnl, m, 0, NULL);
        if (r == -ENODEV) /* Already gone */
                return 0;
        if (r < 0)
                return log_error_errno(r, "Failed to remove interface %s: %m", name);

        return 1;
}

static int generate_mac(
                const char *machine_name,
                struct ether_addr *mac,
                sd_id128_t hash_key,
                uint64_t idx) {

        uint64_t result;
        size_t l, sz;
        uint8_t *v, *i;
        int r;

        l = strlen(machine_name);
        sz = sizeof(sd_id128_t) + l;
        if (idx > 0)
                sz += sizeof(idx);

        v = newa(uint8_t, sz);

        /* fetch some persistent data unique to the host */
        r = sd_id128_get_machine((sd_id128_t*) v);
        if (r < 0)
                return r;

        /* combine with some data unique (on this host) to this
         * container instance */
        i = mempcpy(v + sizeof(sd_id128_t), machine_name, l);
        if (idx > 0) {
                idx = htole64(idx);
                memcpy(i, &idx, sizeof(idx));
        }

        /* Let's hash the host machine ID plus the container name. We
         * use a fixed, but originally randomly created hash key here. */
        result = htole64(siphash24(v, sz, hash_key.bytes));

        assert_cc(ETH_ALEN <= sizeof(result));
        memcpy(mac->ether_addr_octet, &result, ETH_ALEN);

        /* see eth_random_addr in the kernel */
        mac->ether_addr_octet[0] &= 0xfe;        /* clear multicast bit */
        mac->ether_addr_octet[0] |= 0x02;        /* set local assignment bit (IEEE802) */

        return 0;
}

static int set_alternative_ifname(sd_netlink *rtnl, const char *ifname, const char *altifname) {
        int r;

        assert(rtnl);
        assert(ifname);

        if (!altifname)
                return 0;

        if (strlen(altifname) >= ALTIFNAMSIZ)
                return log_warning_errno(SYNTHETIC_ERRNO(ERANGE),
                                         "Alternative interface name '%s' for '%s' is too long, ignoring",
                                         altifname, ifname);

        r = rtnl_set_link_alternative_names_by_ifname(&rtnl, ifname, STRV_MAKE(altifname));
        if (r < 0)
                return log_warning_errno(r,
                                         "Failed to set alternative interface name '%s' to '%s', ignoring: %m",
                                         altifname, ifname);

        return 0;
}

static int add_veth(
                sd_netlink *rtnl,
                pid_t pid,
                const char *ifname_host,
                const char *altifname_host,
                const struct ether_addr *mac_host,
                const char *ifname_container,
                const struct ether_addr *mac_container) {

        _cleanup_(sd_netlink_message_unrefp) sd_netlink_message *m = NULL;
        int r;

        assert(rtnl);
        assert(ifname_host);
        assert(mac_host);
        assert(ifname_container);
        assert(mac_container);

        r = sd_rtnl_message_new_link(rtnl, &m, RTM_NEWLINK, 0);
        if (r < 0)
                return log_error_errno(r, "Failed to allocate netlink message: %m");

        r = sd_netlink_message_append_string(m, IFLA_IFNAME, ifname_host);
        if (r < 0)
                return log_error_errno(r, "Failed to add netlink interface name: %m");

        r = sd_netlink_message_append_ether_addr(m, IFLA_ADDRESS, mac_host);
        if (r < 0)
                return log_error_errno(r, "Failed to add netlink MAC address: %m");

        r = sd_netlink_message_open_container(m, IFLA_LINKINFO);
        if (r < 0)
                return log_error_errno(r, "Failed to open netlink container: %m");

        r = sd_netlink_message_open_container_union(m, IFLA_INFO_DATA, "veth");
        if (r < 0)
                return log_error_errno(r, "Failed to open netlink container: %m");

        r = sd_netlink_message_open_container(m, VETH_INFO_PEER);
        if (r < 0)
                return log_error_errno(r, "Failed to open netlink container: %m");

        r = sd_netlink_message_append_string(m, IFLA_IFNAME, ifname_container);
        if (r < 0)
                return log_error_errno(r, "Failed to add netlink interface name: %m");

        r = sd_netlink_message_append_ether_addr(m, IFLA_ADDRESS, mac_container);
        if (r < 0)
                return log_error_errno(r, "Failed to add netlink MAC address: %m");

        r = sd_netlink_message_append_u32(m, IFLA_NET_NS_PID, pid);
        if (r < 0)
                return log_error_errno(r, "Failed to add netlink namespace field: %m");

        r = sd_netlink_message_close_container(m);
        if (r < 0)
                return log_error_errno(r, "Failed to close netlink container: %m");

        r = sd_netlink_message_close_container(m);
        if (r < 0)
                return log_error_errno(r, "Failed to close netlink container: %m");

        r = sd_netlink_message_close_container(m);
        if (r < 0)
                return log_error_errno(r, "Failed to close netlink container: %m");

        r = sd_netlink_call(rtnl, m, 0, NULL);
        if (r < 0)
                return log_error_errno(r, "Failed to add new veth interfaces (%s:%s): %m", ifname_host, ifname_container);

        (void) set_alternative_ifname(rtnl, ifname_host, altifname_host);

        return 0;
}

static int shorten_ifname(char *ifname) {
        char new_ifname[IFNAMSIZ];

        assert(ifname);

        if (strlen(ifname) < IFNAMSIZ) /* Name is short enough */
                return 0;

        if (naming_scheme_has(NAMING_NSPAWN_LONG_HASH)) {
                uint64_t h;

                /* Calculate 64bit hash value */
                h = siphash24(ifname, strlen(ifname), SHORTEN_IFNAME_HASH_KEY.bytes);

                /* Set the final four bytes (i.e. 32bit) to the lower 24bit of the hash, encoded in url-safe base64 */
                memcpy(new_ifname, ifname, IFNAMSIZ - 5);
                new_ifname[IFNAMSIZ - 5] = urlsafe_base64char(h >> 18);
                new_ifname[IFNAMSIZ - 4] = urlsafe_base64char(h >> 12);
                new_ifname[IFNAMSIZ - 3] = urlsafe_base64char(h >> 6);
                new_ifname[IFNAMSIZ - 2] = urlsafe_base64char(h);
        } else
                /* On old nspawn versions we just truncated the name, provide compatibility */
                memcpy(new_ifname, ifname, IFNAMSIZ-1);

        new_ifname[IFNAMSIZ - 1] = 0;

        /* Log the incident to make it more discoverable */
        log_warning("Network interface name '%s' has been changed to '%s' to fit length constraints.", ifname, new_ifname);

        strcpy(ifname, new_ifname);
        return 1;
}

int setup_veth(const char *machine_name,
               pid_t pid,
               char iface_name[IFNAMSIZ],
               bool bridge) {

        _cleanup_(sd_netlink_unrefp) sd_netlink *rtnl = NULL;
        struct ether_addr mac_host, mac_container;
        unsigned u;
        char *n, *a = NULL;
        int r;

        assert(machine_name);
        assert(pid > 0);
        assert(iface_name);

        /* Use two different interface name prefixes depending whether
         * we are in bridge mode or not. */
        n = strjoina(bridge ? "vb-" : "ve-", machine_name);
        r = shorten_ifname(n);
        if (r > 0)
                a = strjoina(bridge ? "vb-" : "ve-", machine_name);

        r = generate_mac(machine_name, &mac_container, CONTAINER_HASH_KEY, 0);
        if (r < 0)
                return log_error_errno(r, "Failed to generate predictable MAC address for container side: %m");

        r = generate_mac(machine_name, &mac_host, HOST_HASH_KEY, 0);
        if (r < 0)
                return log_error_errno(r, "Failed to generate predictable MAC address for host side: %m");

        r = sd_netlink_open(&rtnl);
        if (r < 0)
                return log_error_errno(r, "Failed to connect to netlink: %m");

        r = add_veth(rtnl, pid, n, a, &mac_host, "host0", &mac_container);
        if (r < 0)
                return r;

        u = if_nametoindex(n); /* We don't need to use rtnl_resolve_ifname() here because the
                                * name we assigned is always the main name. */
        if (u == 0)
                return log_error_errno(errno, "Failed to resolve interface %s: %m", n);

        strcpy(iface_name, n);
        return (int) u;
}

int setup_veth_extra(
                const char *machine_name,
                pid_t pid,
                char **pairs) {

        _cleanup_(sd_netlink_unrefp) sd_netlink *rtnl = NULL;
        uint64_t idx = 0;
        int r;

        assert(machine_name);
        assert(pid > 0);

        if (strv_isempty(pairs))
                return 0;

        r = sd_netlink_open(&rtnl);
        if (r < 0)
                return log_error_errno(r, "Failed to connect to netlink: %m");

        STRV_FOREACH_PAIR(a, b, pairs) {
                struct ether_addr mac_host, mac_container;

                r = generate_mac(machine_name, &mac_container, VETH_EXTRA_CONTAINER_HASH_KEY, idx);
                if (r < 0)
                        return log_error_errno(r, "Failed to generate predictable MAC address for container side of extra veth link: %m");

                r = generate_mac(machine_name, &mac_host, VETH_EXTRA_HOST_HASH_KEY, idx);
                if (r < 0)
                        return log_error_errno(r, "Failed to generate predictable MAC address for host side of extra veth link: %m");

                r = add_veth(rtnl, pid, *a, NULL, &mac_host, *b, &mac_container);
                if (r < 0)
                        return r;

                idx++;
        }

        return 0;
}

static int join_bridge(sd_netlink *rtnl, const char *veth_name, const char *bridge_name) {
        _cleanup_(sd_netlink_message_unrefp) sd_netlink_message *m = NULL;
        int r, bridge_ifi;

        assert(rtnl);
        assert(veth_name);
        assert(bridge_name);

        bridge_ifi = rtnl_resolve_interface(&rtnl, bridge_name);
        if (bridge_ifi < 0)
                return bridge_ifi;

        r = sd_rtnl_message_new_link(rtnl, &m, RTM_SETLINK, 0);
        if (r < 0)
                return r;

        r = sd_rtnl_message_link_set_flags(m, IFF_UP, IFF_UP);
        if (r < 0)
                return r;

        r = sd_netlink_message_append_string(m, IFLA_IFNAME, veth_name);
        if (r < 0)
                return r;

        r = sd_netlink_message_append_u32(m, IFLA_MASTER, bridge_ifi);
        if (r < 0)
                return r;

        r = sd_netlink_call(rtnl, m, 0, NULL);
        if (r < 0)
                return r;

        return bridge_ifi;
}

static int create_bridge(sd_netlink *rtnl, const char *bridge_name) {
        _cleanup_(sd_netlink_message_unrefp) sd_netlink_message *m = NULL;
        int r;

        r = sd_rtnl_message_new_link(rtnl, &m, RTM_NEWLINK, 0);
        if (r < 0)
                return r;

        r = sd_netlink_message_append_string(m, IFLA_IFNAME, bridge_name);
        if (r < 0)
                return r;

        r = sd_netlink_message_open_container(m, IFLA_LINKINFO);
        if (r < 0)
                return r;

        r = sd_netlink_message_open_container_union(m, IFLA_INFO_DATA, "bridge");
        if (r < 0)
                return r;

        r = sd_netlink_message_close_container(m);
        if (r < 0)
                return r;

        r = sd_netlink_message_close_container(m);
        if (r < 0)
                return r;

        r = sd_netlink_call(rtnl, m, 0, NULL);
        if (r < 0)
                return r;

        return 0;
}

int setup_bridge(const char *veth_name, const char *bridge_name, bool create) {
        _cleanup_(release_lock_file) LockFile bridge_lock = LOCK_FILE_INIT;
        _cleanup_(sd_netlink_unrefp) sd_netlink *rtnl = NULL;
        int r, bridge_ifi;
        unsigned n = 0;

        assert(veth_name);
        assert(bridge_name);

        r = sd_netlink_open(&rtnl);
        if (r < 0)
                return log_error_errno(r, "Failed to connect to netlink: %m");

        if (create) {
                /* We take a system-wide lock here, so that we can safely check whether there's still a member in the
                 * bridge before removing it, without risking interference from other nspawn instances. */

                r = make_lock_file("/run/systemd/nspawn-network-zone", LOCK_EX, &bridge_lock);
                if (r < 0)
                        return log_error_errno(r, "Failed to take network zone lock: %m");
        }

        for (;;) {
                bridge_ifi = join_bridge(rtnl, veth_name, bridge_name);
                if (bridge_ifi >= 0)
                        return bridge_ifi;
                if (bridge_ifi != -ENODEV || !create || n > 10)
                        return log_error_errno(bridge_ifi, "Failed to add interface %s to bridge %s: %m", veth_name, bridge_name);

                /* Count attempts, so that we don't enter an endless loop here. */
                n++;

                /* The bridge doesn't exist yet. Let's create it */
                r = create_bridge(rtnl, bridge_name);
                if (r < 0)
                        return log_error_errno(r, "Failed to create bridge interface %s: %m", bridge_name);

                /* Try again, now that the bridge exists */
        }
}

int remove_bridge(const char *bridge_name) {
        _cleanup_(release_lock_file) LockFile bridge_lock = LOCK_FILE_INIT;
        _cleanup_(sd_netlink_unrefp) sd_netlink *rtnl = NULL;
        const char *path;
        int r;

        /* Removes the specified bridge, but only if it is currently empty */

        if (isempty(bridge_name))
                return 0;

        r = make_lock_file("/run/systemd/nspawn-network-zone", LOCK_EX, &bridge_lock);
        if (r < 0)
                return log_error_errno(r, "Failed to take network zone lock: %m");

        path = strjoina("/sys/class/net/", bridge_name, "/brif");

        r = dir_is_empty(path, /* ignore_hidden_or_backup= */ false);
        if (r == -ENOENT) /* Already gone? */
                return 0;
        if (r < 0)
                return log_error_errno(r, "Can't detect if bridge %s is empty: %m", bridge_name);
        if (r == 0) /* Still populated, leave it around */
                return 0;

        r = sd_netlink_open(&rtnl);
        if (r < 0)
                return log_error_errno(r, "Failed to connect to netlink: %m");

        return remove_one_link(rtnl, bridge_name);
}

int test_network_interface_initialized(const char *name) {
        _cleanup_(sd_device_unrefp) sd_device *d = NULL;
        int r;

        if (!udev_available())
                return 0;

        /* udev should be around. */

        r = sd_device_new_from_ifname(&d, name);
        if (r < 0)
                return log_error_errno(r, "Failed to get device %s: %m", name);

        r = sd_device_get_is_initialized(d);
        if (r < 0)
                return log_error_errno(r, "Failed to determine whether interface %s is initialized: %m", name);
        if (r == 0)
                return log_error_errno(SYNTHETIC_ERRNO(EBUSY), "Network interface %s is not initialized yet.", name);

        r = device_is_renaming(d);
        if (r < 0)
                return log_error_errno(r, "Failed to determine the interface %s is being renamed: %m", name);
        if (r > 0)
                return log_error_errno(SYNTHETIC_ERRNO(EBUSY), "Interface %s is being renamed.", name);

        return 0;
}

int move_network_interfaces(int netns_fd, char **ifaces) {
        _cleanup_(sd_netlink_unrefp) sd_netlink *rtnl = NULL;
        int r;

        if (strv_isempty(ifaces))
                return 0;

        r = sd_netlink_open(&rtnl);
        if (r < 0)
                return log_error_errno(r, "Failed to connect to netlink: %m");

        STRV_FOREACH(i, ifaces) {
                _cleanup_(sd_netlink_message_unrefp) sd_netlink_message *m = NULL;
                int ifi;

                ifi = rtnl_resolve_interface_or_warn(&rtnl, *i);
                if (ifi < 0)
                        return ifi;

                r = sd_rtnl_message_new_link(rtnl, &m, RTM_SETLINK, ifi);
                if (r < 0)
                        return log_error_errno(r, "Failed to allocate netlink message: %m");

                r = sd_netlink_message_append_u32(m, IFLA_NET_NS_FD, netns_fd);
                if (r < 0)
                        return log_error_errno(r, "Failed to append namespace fd to netlink message: %m");

                r = sd_netlink_call(rtnl, m, 0, NULL);
                if (r < 0)
                        return log_error_errno(r, "Failed to move interface %s to namespace: %m", *i);
        }

        return 0;
}

int setup_macvlan(const char *machine_name, pid_t pid, char **ifaces) {
        _cleanup_(sd_netlink_unrefp) sd_netlink *rtnl = NULL;
        unsigned idx = 0;
        int r;

        if (strv_isempty(ifaces))
                return 0;

        r = sd_netlink_open(&rtnl);
        if (r < 0)
                return log_error_errno(r, "Failed to connect to netlink: %m");

        STRV_FOREACH(i, ifaces) {
                _cleanup_(sd_netlink_message_unrefp) sd_netlink_message *m = NULL;
                _cleanup_free_ char *n = NULL, *a = NULL;
                struct ether_addr mac;
                int ifi;

                ifi = rtnl_resolve_interface_or_warn(&rtnl, *i);
                if (ifi < 0)
                        return ifi;

                r = generate_mac(machine_name, &mac, MACVLAN_HASH_KEY, idx++);
                if (r < 0)
                        return log_error_errno(r, "Failed to create MACVLAN MAC address: %m");

                r = sd_rtnl_message_new_link(rtnl, &m, RTM_NEWLINK, 0);
                if (r < 0)
                        return log_error_errno(r, "Failed to allocate netlink message: %m");

                r = sd_netlink_message_append_u32(m, IFLA_LINK, ifi);
                if (r < 0)
                        return log_error_errno(r, "Failed to add netlink interface index: %m");

                n = strjoin("mv-", *i);
                if (!n)
                        return log_oom();

                r = shorten_ifname(n);
                if (r > 0) {
                        a = strjoin("mv-", *i);
                        if (!a)
                                return log_oom();
                }

                r = sd_netlink_message_append_string(m, IFLA_IFNAME, n);
                if (r < 0)
                        return log_error_errno(r, "Failed to add netlink interface name: %m");

                r = sd_netlink_message_append_ether_addr(m, IFLA_ADDRESS, &mac);
                if (r < 0)
                        return log_error_errno(r, "Failed to add netlink MAC address: %m");

                r = sd_netlink_message_append_u32(m, IFLA_NET_NS_PID, pid);
                if (r < 0)
                        return log_error_errno(r, "Failed to add netlink namespace field: %m");

                r = sd_netlink_message_open_container(m, IFLA_LINKINFO);
                if (r < 0)
                        return log_error_errno(r, "Failed to open netlink container: %m");

                r = sd_netlink_message_open_container_union(m, IFLA_INFO_DATA, "macvlan");
                if (r < 0)
                        return log_error_errno(r, "Failed to open netlink container: %m");

                r = sd_netlink_message_append_u32(m, IFLA_MACVLAN_MODE, MACVLAN_MODE_BRIDGE);
                if (r < 0)
                        return log_error_errno(r, "Failed to append macvlan mode: %m");

                r = sd_netlink_message_close_container(m);
                if (r < 0)
                        return log_error_errno(r, "Failed to close netlink container: %m");

                r = sd_netlink_message_close_container(m);
                if (r < 0)
                        return log_error_errno(r, "Failed to close netlink container: %m");

                r = sd_netlink_call(rtnl, m, 0, NULL);
                if (r < 0)
                        return log_error_errno(r, "Failed to add new macvlan interfaces: %m");

                (void) set_alternative_ifname(rtnl, n, a);
        }

        return 0;
}

int setup_ipvlan(const char *machine_name, pid_t pid, char **ifaces) {
        _cleanup_(sd_netlink_unrefp) sd_netlink *rtnl = NULL;
        int r;

        if (strv_isempty(ifaces))
                return 0;

        r = sd_netlink_open(&rtnl);
        if (r < 0)
                return log_error_errno(r, "Failed to connect to netlink: %m");

        STRV_FOREACH(i, ifaces) {
                _cleanup_(sd_netlink_message_unrefp) sd_netlink_message *m = NULL;
                _cleanup_free_ char *n = NULL, *a = NULL;
                int ifi;

                ifi = rtnl_resolve_interface_or_warn(&rtnl, *i);
                if (ifi < 0)
                        return ifi;

                r = sd_rtnl_message_new_link(rtnl, &m, RTM_NEWLINK, 0);
                if (r < 0)
                        return log_error_errno(r, "Failed to allocate netlink message: %m");

                r = sd_netlink_message_append_u32(m, IFLA_LINK, ifi);
                if (r < 0)
                        return log_error_errno(r, "Failed to add netlink interface index: %m");

                n = strjoin("iv-", *i);
                if (!n)
                        return log_oom();

                r = shorten_ifname(n);
                if (r > 0) {
                        a = strjoin("iv-", *i);
                        if (!a)
                                return log_oom();
                }

                r = sd_netlink_message_append_string(m, IFLA_IFNAME, n);
                if (r < 0)
                        return log_error_errno(r, "Failed to add netlink interface name: %m");

                r = sd_netlink_message_append_u32(m, IFLA_NET_NS_PID, pid);
                if (r < 0)
                        return log_error_errno(r, "Failed to add netlink namespace field: %m");

                r = sd_netlink_message_open_container(m, IFLA_LINKINFO);
                if (r < 0)
                        return log_error_errno(r, "Failed to open netlink container: %m");

                r = sd_netlink_message_open_container_union(m, IFLA_INFO_DATA, "ipvlan");
                if (r < 0)
                        return log_error_errno(r, "Failed to open netlink container: %m");

                r = sd_netlink_message_append_u16(m, IFLA_IPVLAN_MODE, IPVLAN_MODE_L2);
                if (r < 0)
                        return log_error_errno(r, "Failed to add ipvlan mode: %m");

                r = sd_netlink_message_close_container(m);
                if (r < 0)
                        return log_error_errno(r, "Failed to close netlink container: %m");

                r = sd_netlink_message_close_container(m);
                if (r < 0)
                        return log_error_errno(r, "Failed to close netlink container: %m");

                r = sd_netlink_call(rtnl, m, 0, NULL);
                if (r < 0)
                        return log_error_errno(r, "Failed to add new ipvlan interfaces: %m");

                (void) set_alternative_ifname(rtnl, n, a);
        }

        return 0;
}

int veth_extra_parse(char ***l, const char *p) {
        _cleanup_free_ char *a = NULL, *b = NULL;
        int r;

        r = extract_first_word(&p, &a, ":", EXTRACT_DONT_COALESCE_SEPARATORS);
        if (r < 0)
                return r;
        if (r == 0 || !ifname_valid(a))
                return -EINVAL;

        r = extract_first_word(&p, &b, ":", EXTRACT_DONT_COALESCE_SEPARATORS);
        if (r < 0)
                return r;
        if (r == 0 || !ifname_valid(b)) {
                free(b);
                b = strdup(a);
                if (!b)
                        return -ENOMEM;
        }

        if (p)
                return -EINVAL;

        r = strv_push_pair(l, a, b);
        if (r < 0)
                return -ENOMEM;

        a = b = NULL;
        return 0;
}

int remove_veth_links(const char *primary, char **pairs) {
        _cleanup_(sd_netlink_unrefp) sd_netlink *rtnl = NULL;
        int r;

        /* In some cases the kernel might pin the veth links between host and container even after the namespace
         * died. Hence, let's better remove them explicitly too. */

        if (isempty(primary) && strv_isempty(pairs))
                return 0;

        r = sd_netlink_open(&rtnl);
        if (r < 0)
                return log_error_errno(r, "Failed to connect to netlink: %m");

        remove_one_link(rtnl, primary);

        STRV_FOREACH_PAIR(a, b, pairs)
                remove_one_link(rtnl, *a);

        return 0;
}