libsystemd-networkd: introduce sd-pppoe library

This library negotiates a PPPoE channel. It handles the discovery stage and
leaves the session stage to the kernel. A further PPP library is needed to
actually set up a PPP unit (negotatie LCP, IPCP and do authentication), so in
isolation this is not yet very useful.

The test program has two modes:

  # ./test-pppoe

will create a veth tunnel in a new network namespace, start pppoe-server on one
end and this client library on the other. The pppd server will time out as no
LCP is performed, and the client will then shut down gracefully.

  # ./test-pppoe eth0

will run the client on eth0 (or any other netdev), and requires a PPPoE server
to be reachable on the local link.

1 files changed, 808 insertions, 0 deletions

diff --git a/src/libsystemd-network/sd-pppoe.c b/src/libsystemd-network/sd-pppoe.c
new file mode 100644
index 0000000000..17b2d6dab6
--- /dev/null
+++ b/src/libsystemd-network/sd-pppoe.c
@@ -0,0 +1,808 @@
+/*-*- Mode: C; c-basic-offset: 8; indent-tabs-mode: nil -*-*/
+
+/***
+  This file is part of systemd.
+
+  Copyright (C) 2014 Tom Gundersen
+
+  systemd is free software; you can redistribute it and/or modify it
+  under the terms of the GNU Lesser General Public License as published by
+  the Free Software Foundation; either version 2.1 of the License, or
+  (at your option) any later version.
+
+  systemd is distributed in the hope that it will be useful, but
+  WITHOUT ANY WARRANTY; without even the implied warranty of
+  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+  Lesser General Public License for more details.
+
+  You should have received a copy of the GNU Lesser General Public License
+  along with systemd; If not, see <http://www.gnu.org/licenses/>.
+***/
+
+/* See RFC 2516 */
+
+#include <sys/ioctl.h>
+#include <linux/ppp-ioctl.h>
+#include <net/if.h>
+#include <netinet/in.h>
+#include <linux/if_pppox.h>
+
+#include "sd-pppoe.h"
+
+#include "event-util.h"
+
+#include "util.h"
+#include "socket-util.h"
+#include "async.h"
+#include "refcnt.h"
+#include "unaligned.h"
+#include "utf8.h"
+
+#define PPPOE_MAX_PACKET_SIZE 1484
+#define PPPOE_MAX_PADR_RESEND 16
+
+/* TODO: move this to socket-util.h without getting into
+ * a mess with the includes */
+union sockaddr_union_pppox {
+        struct sockaddr sa;
+        struct sockaddr_pppox pppox;
+};
+
+typedef enum PPPoEState {
+        PPPOE_STATE_INITIALIZING,
+        PPPOE_STATE_REQUESTING,
+        PPPOE_STATE_RUNNING,
+        PPPOE_STATE_STOPPED,
+        _PPPOE_STATE_MAX,
+        _PPPOE_STATE_INVALID = -1,
+} PPPoEState;
+
+typedef struct PPPoETags {
+                char *service_name;
+                char *ac_name;
+                uint8_t *host_uniq;
+                size_t host_uniq_len;
+                uint8_t *cookie;
+                size_t cookie_len;
+} PPPoETags;
+
+struct sd_pppoe {
+        RefCount n_ref;
+
+        PPPoEState state;
+        uint64_t host_uniq;
+
+        int ifindex;
+        char *ifname;
+
+        sd_event *event;
+        int event_priority;
+        int fd;
+        sd_event_source *io;
+        sd_event_source *timeout;
+        int padr_resend_count;
+
+        char *service_name;
+        struct ether_addr peer_mac;
+        be16_t session_id;
+
+        int pppoe_fd;
+        int channel;
+
+        sd_pppoe_cb_t cb;
+        void *userdata;
+
+        PPPoETags tags;
+};
+
+#define PPPOE_PACKET_LENGTH(header) \
+        be16toh((header)->length)
+
+#define PPPOE_PACKET_TAIL(packet)                                                                               \
+        (struct pppoe_tag *)((uint8_t*)(packet) + sizeof(struct pppoe_hdr) + PPPOE_PACKET_LENGTH(packet))
+
+#define PPPOE_TAG_LENGTH(tag)                   \
+        unaligned_read_be16(&(tag)->tag_len)
+
+#define PPPOE_TAG_TYPE(tag)                     \
+        htobe16(unaligned_read_be16(&(tag)->tag_type))
+
+#define PPPOE_TAG_SET_LENGTH(tag, len) \
+        unaligned_write_be16(&(tag)->tag_len, len)
+
+#define PPPOE_TAG_SET_TYPE(tag, len) \
+        unaligned_write_be16(&(tag)->tag_type, be16toh(len))
+
+#define PPPOE_TAG_NEXT(tag)                                                                      \
+        (struct pppoe_tag *)((uint8_t *)(tag) + sizeof(struct pppoe_tag) + PPPOE_TAG_LENGTH(tag))
+
+#define PPPOE_TAGS_FOREACH(tag, header)                                                                 \
+        for (tag = (header)->tag;                                                                       \
+             ((uint8_t *)(tag) + sizeof(struct pppoe_tag) < (uint8_t*)PPPOE_PACKET_TAIL(header)) &&     \
+                (PPPOE_TAG_NEXT(tag) <= PPPOE_PACKET_TAIL(header)) &&                                   \
+                (tag >= (header)->tag) &&                                                               \
+                (PPPOE_TAG_TYPE(tag) != PTT_EOL);                                                           \
+             tag = PPPOE_TAG_NEXT(tag))
+
+static void pppoe_tags_clear(PPPoETags *tags) {
+        free(tags->service_name);
+        free(tags->ac_name);
+        free(tags->host_uniq);
+        free(tags->cookie);
+
+        zero(*tags);
+}
+
+int sd_pppoe_set_ifindex(sd_pppoe *ppp, int ifindex) {
+        assert_return(ppp, -EINVAL);
+        assert_return(ifindex > 0, -EINVAL);
+
+        ppp->ifindex = ifindex;
+
+        return 0;
+}
+
+int sd_pppoe_set_ifname(sd_pppoe *ppp, const char *ifname) {
+        char *name;
+
+        assert_return(ppp, -EINVAL);
+        assert_return(ifname, -EINVAL);
+
+        if (strlen(ifname) > IFNAMSIZ)
+                return -EINVAL;
+
+        name = strdup(ifname);
+        if (!name)
+                return -ENOMEM;
+
+        free(ppp->ifname);
+        ppp->ifname = name;
+
+        return 0;
+}
+
+int sd_pppoe_set_service_name(sd_pppoe *ppp, const char *service_name) {
+        _cleanup_free_ char *name = NULL;
+
+        assert_return(ppp, -EINVAL);
+
+        if (service_name) {
+                name = strdup(service_name);
+                if (!name)
+                        return -ENOMEM;
+        }
+
+        free(ppp->service_name);
+        ppp->service_name = name;
+        name = NULL;
+
+        return 0;
+}
+
+int sd_pppoe_attach_event(sd_pppoe *ppp, sd_event *event, int priority) {
+        int r;
+
+        assert_return(ppp, -EINVAL);
+        assert_return(!ppp->event, -EBUSY);
+
+        if (event)
+                ppp->event = sd_event_ref(event);
+        else {
+                r = sd_event_default(&ppp->event);
+                if (r < 0)
+                        return r;
+        }
+
+        ppp->event_priority = priority;
+
+        return 0;
+}
+
+int sd_pppoe_detach_event(sd_pppoe *ppp) {
+        assert_return(ppp, -EINVAL);
+
+        ppp->event = sd_event_unref(ppp->event);
+
+        return 0;
+}
+
+sd_pppoe *sd_pppoe_ref(sd_pppoe *ppp) {
+        if (ppp)
+                assert_se(REFCNT_INC(ppp->n_ref) >= 2);
+
+        return ppp;
+}
+
+sd_pppoe *sd_pppoe_unref(sd_pppoe *ppp) {
+        if (ppp && REFCNT_DEC(ppp->n_ref) <= 0) {
+                pppoe_tags_clear(&ppp->tags);
+                sd_pppoe_stop(ppp);
+                sd_pppoe_detach_event(ppp);
+
+                free(ppp);
+        }
+
+        return NULL;
+}
+
+int sd_pppoe_new (sd_pppoe **ret) {
+        sd_pppoe *ppp;
+
+        assert_return(ret, -EINVAL);
+
+        ppp = new0(sd_pppoe, 1);
+        if (!ppp)
+                return -ENOMEM;
+
+        ppp->n_ref = REFCNT_INIT;
+        ppp->state = _PPPOE_STATE_INVALID;
+        ppp->ifindex = -1;
+        ppp->fd = -1;
+        ppp->pppoe_fd = -1;
+        ppp->padr_resend_count = PPPOE_MAX_PADR_RESEND;
+
+        *ret = ppp;
+
+        return 0;
+}
+
+int sd_pppoe_get_channel(sd_pppoe *ppp, int *channel) {
+        assert_return(ppp, -EINVAL);
+        assert_return(channel, -EINVAL);
+        assert_return(ppp->pppoe_fd != -1, -EUNATCH);
+        assert_return(ppp->state == PPPOE_STATE_RUNNING, -EUNATCH);
+
+        *channel = ppp->channel;
+
+        return 0;
+}
+
+int sd_pppoe_set_callback(sd_pppoe *ppp, sd_pppoe_cb_t cb, void *userdata) {
+        assert_return(ppp, -EINVAL);
+
+        ppp->cb = cb;
+        ppp->userdata = userdata;
+
+        return 0;
+}
+
+static void pppoe_tag_append(struct pppoe_hdr *packet, size_t packet_size, be16_t tag_type, const void *tag_data, uint16_t tag_len) {
+        struct pppoe_tag *tag;
+
+        assert(packet);
+        assert(sizeof(struct pppoe_hdr) + PPPOE_PACKET_LENGTH(packet) + sizeof(struct pppoe_tag) + tag_len <= packet_size);
+        assert(!(!tag_data ^ !tag_len));
+
+        tag = PPPOE_PACKET_TAIL(packet);
+
+        PPPOE_TAG_SET_LENGTH(tag, tag_len);
+        PPPOE_TAG_SET_TYPE(tag, tag_type);
+        if (tag_data)
+                memcpy(tag->tag_data, tag_data, tag_len);
+
+        packet->length = htobe16(PPPOE_PACKET_LENGTH(packet) + sizeof(struct pppoe_tag) + tag_len);
+}
+
+static int pppoe_send(sd_pppoe *ppp, uint8_t code) {
+        union sockaddr_union link = {
+                .ll = {
+                        .sll_family = AF_PACKET,
+                        .sll_protocol = htons(ETH_P_PPP_DISC),
+                        .sll_halen = ETH_ALEN,
+                },
+        };
+        _cleanup_free_ struct pppoe_hdr *packet = NULL;
+        int r;
+
+        assert(ppp);
+        assert(ppp->fd != -1);
+        assert(IN_SET(code, PADI_CODE, PADR_CODE, PADT_CODE));
+
+        link.ll.sll_ifindex = ppp->ifindex;
+        if (code == PADI_CODE)
+                memset(&link.ll.sll_addr, 0xff, ETH_ALEN);
+        else
+                memcpy(&link.ll.sll_addr, &ppp->peer_mac, ETH_ALEN);
+
+        packet = malloc0(PPPOE_MAX_PACKET_SIZE);
+        if (!packet)
+                return -ENOMEM;
+
+        packet->ver = 0x1;
+        packet->type = 0x1;
+        packet->code = code;
+        if (code == PADT_CODE)
+                packet->sid = ppp->session_id;
+
+        /* Service-Name */
+        pppoe_tag_append(packet, PPPOE_MAX_PACKET_SIZE, PTT_SRV_NAME,
+                         ppp->service_name, ppp->service_name ? strlen(ppp->service_name) : 0);
+
+        /* AC-Cookie */
+        if (code == PADR_CODE && ppp->tags.cookie)
+                pppoe_tag_append(packet, PPPOE_MAX_PACKET_SIZE, PTT_AC_COOKIE,
+                                 ppp->tags.cookie, ppp->tags.cookie_len);
+
+        /* Host-Uniq */
+        if (code != PADT_CODE) {
+                ppp->host_uniq = random_u64();
+
+                pppoe_tag_append(packet, PPPOE_MAX_PACKET_SIZE, PTT_HOST_UNIQ,
+                                 &ppp->host_uniq, sizeof(ppp->host_uniq));
+        }
+
+        r = sendto(ppp->fd, packet, sizeof(struct pppoe_hdr) + PPPOE_PACKET_LENGTH(packet),
+                   0, &link.sa, sizeof(link.ll));
+        if (r < 0)
+                return -errno;
+
+        return 0;
+}
+
+static int pppoe_timeout(sd_event_source *s, uint64_t usec, void *userdata);
+
+static int pppoe_arm_timeout(sd_pppoe *ppp) {
+        _cleanup_event_source_unref_ sd_event_source *timeout = NULL;
+        usec_t next_timeout;
+        int r;
+
+        assert(ppp);
+
+        r = sd_event_now(ppp->event, clock_boottime_or_monotonic(), &next_timeout);
+        if (r == -ENODATA)
+                next_timeout = now(clock_boottime_or_monotonic());
+        else if (r < 0)
+                return r;
+
+        next_timeout += 500 * USEC_PER_MSEC;
+
+        r = sd_event_add_time(ppp->event, &timeout, clock_boottime_or_monotonic(), next_timeout,
+                              10 * USEC_PER_MSEC, pppoe_timeout, ppp);
+        if (r < 0)
+                return r;
+
+        r = sd_event_source_set_priority(timeout, ppp->event_priority);
+        if (r < 0)
+                return r;
+
+        sd_event_source_unref(ppp->timeout);
+        ppp->timeout = timeout;
+        timeout = NULL;
+
+        return 0;
+}
+
+static int pppoe_send_initiation(sd_pppoe *ppp) {
+        int r;
+
+        r = pppoe_send(ppp, PADI_CODE);
+        if (r < 0)
+                return r;
+
+        log_debug("PPPoE: sent DISCOVER (Service-Name: %s)",
+                  ppp->service_name ? : "");
+
+        pppoe_arm_timeout(ppp);
+
+        return r;
+}
+
+static int pppoe_send_request(sd_pppoe *ppp) {
+        int r;
+
+        r = pppoe_send(ppp, PADR_CODE);
+        if (r < 0)
+                return r;
+
+        log_debug("PPPoE: sent REQUEST");
+
+        ppp->padr_resend_count --;
+
+        pppoe_arm_timeout(ppp);
+
+        return 0;
+}
+
+static int pppoe_send_terminate(sd_pppoe *ppp) {
+        int r;
+
+        r = pppoe_send(ppp, PADT_CODE);
+        if (r < 0)
+                return r;
+
+        log_debug("PPPoE: sent TERMINATE");
+
+        return 0;
+}
+
+static int pppoe_timeout(sd_event_source *s, uint64_t usec, void *userdata) {
+        sd_pppoe *ppp = userdata;
+        int r;
+
+        assert(ppp);
+
+        switch (ppp->state) {
+        case PPPOE_STATE_INITIALIZING:
+                r = pppoe_send_initiation(ppp);
+                if (r < 0)
+                        log_warning("PPPoE: sending PADI failed: %s", strerror(-r));
+
+                break;
+        case PPPOE_STATE_REQUESTING:
+                if (ppp->padr_resend_count <= 0) {
+                        log_debug("PPPoE: PADR timed out, restarting PADI");
+
+                        r = pppoe_send_initiation(ppp);
+                        if (r < 0)
+                                log_warning("PPPoE: sending PADI failed: %s", strerror(-r));
+
+                        ppp->padr_resend_count = PPPOE_MAX_PADR_RESEND;
+                        ppp->state = PPPOE_STATE_INITIALIZING;
+                } else {
+                        r = pppoe_send_request(ppp);
+                        if (r < 0)
+                                log_warning("PPPoE: sending PADR failed: %s", strerror(-r));
+                }
+
+                break;
+        default:
+                assert_not_reached("timeout in invalid state");
+        }
+
+        return 0;
+}
+
+static int pppoe_tag_parse_binary(struct pppoe_tag *tag, uint8_t **ret, size_t *length) {
+        uint8_t *data;
+
+        assert(ret);
+        assert(length);
+
+        data = memdup(tag->tag_data, PPPOE_TAG_LENGTH(tag));
+        if (!data)
+                return -ENOMEM;
+
+        free(*ret);
+        *ret = data;
+        *length = PPPOE_TAG_LENGTH(tag);
+
+        return 0;
+}
+
+static int pppoe_tag_parse_string(struct pppoe_tag *tag, char **ret) {
+        char *string;
+
+        assert(ret);
+
+        string = strndup(tag->tag_data, PPPOE_TAG_LENGTH(tag));
+        if (!string)
+                return -ENOMEM;
+
+        free(*ret);
+        *ret = string;
+
+        return 0;
+}
+
+static int pppoe_payload_parse(PPPoETags *tags, struct pppoe_hdr *header) {
+        struct pppoe_tag *tag;
+        int r;
+
+        assert(tags);
+
+        pppoe_tags_clear(tags);
+
+        PPPOE_TAGS_FOREACH(tag, header) {
+                switch (PPPOE_TAG_TYPE(tag)) {
+                case PTT_SRV_NAME:
+                        r = pppoe_tag_parse_string(tag, &tags->service_name);
+                        if (r < 0)
+                                return r;
+
+                        break;
+                case PTT_AC_NAME:
+                        r = pppoe_tag_parse_string(tag, &tags->ac_name);
+                        if (r < 0)
+                                return r;
+
+                        break;
+                case PTT_HOST_UNIQ:
+                        r = pppoe_tag_parse_binary(tag, &tags->host_uniq, &tags->host_uniq_len);
+                        if (r < 0)
+                                return r;
+
+                        break;
+                case PTT_AC_COOKIE:
+                        r = pppoe_tag_parse_binary(tag, &tags->cookie, &tags->cookie_len);
+                        if (r < 0)
+                                return r;
+
+                        break;
+                case PTT_SRV_ERR:
+                case PTT_SYS_ERR:
+                case PTT_GEN_ERR:
+                {
+                        _cleanup_free_ char *error = NULL;
+
+                        /* TODO: do something more sensible with the error messages */
+                        r = pppoe_tag_parse_string(tag, &error);
+                        if (r < 0)
+                                return r;
+
+                        if (strlen(error) > 0 && utf8_is_valid(error))
+                                log_debug("PPPoE: error - '%s'", error);
+                        else
+                                log_debug("PPPoE: error");
+
+                        break;
+                }
+                default:
+                        log_debug("PPPoE: ignoring unknown PPPoE tag type: 0x%.2x", PPPOE_TAG_TYPE(tag));
+                }
+        }
+
+        return 0;
+}
+
+static int pppoe_open_pppoe_socket(sd_pppoe *ppp) {
+        int s;
+
+        assert(ppp);
+        assert(ppp->pppoe_fd == -1);
+
+        s = socket(AF_PPPOX, SOCK_STREAM, 0);
+        if (s < 0)
+                return -errno;
+
+        ppp->pppoe_fd = s;
+
+        return 0;
+}
+
+static int pppoe_connect_pppoe_socket(sd_pppoe *ppp) {
+        union sockaddr_union_pppox link = {
+                .pppox = {
+                        .sa_family = AF_PPPOX,
+                        .sa_protocol = PX_PROTO_OE,
+                },
+        };
+        int r, channel;
+
+        assert(ppp);
+        assert(ppp->pppoe_fd != -1);
+        assert(ppp->session_id);
+        assert(ppp->ifname);
+
+        link.pppox.sa_addr.pppoe.sid = ppp->session_id;
+        memcpy(link.pppox.sa_addr.pppoe.dev, ppp->ifname, strlen(ppp->ifname));
+        memcpy(link.pppox.sa_addr.pppoe.remote, &ppp->peer_mac, ETH_ALEN);
+
+        r = connect(ppp->pppoe_fd, &link.sa, sizeof(link.pppox));
+        if (r < 0)
+                return r;
+
+        r = ioctl(ppp->pppoe_fd, PPPIOCGCHAN, &channel);
+        if (r < 0)
+                return -errno;
+
+        ppp->channel = channel;
+
+        return 0;
+}
+
+static int pppoe_handle_message(sd_pppoe *ppp, struct pppoe_hdr *packet, struct ether_addr *mac) {
+        int r;
+
+        assert(packet);
+
+        if (packet->ver != 0x1 || packet->type != 0x1)
+                return 0;
+
+        r = pppoe_payload_parse(&ppp->tags, packet);
+        if (r < 0)
+                return 0;
+
+        switch (ppp->state) {
+        case PPPOE_STATE_INITIALIZING:
+                if (packet->code != PADO_CODE)
+                        return 0;
+
+                if (ppp->tags.host_uniq_len != sizeof(ppp->host_uniq) ||
+                    memcmp(ppp->tags.host_uniq, &ppp->host_uniq, sizeof(ppp->host_uniq)) != 0)
+                        return 0;
+
+                log_debug("PPPoE: got OFFER (Peer: "
+                  "%02hhx:%02hhx:%02hhx:%02hhx:%02hhx:%02hhx; "
+                  "Service-Name: '%s'; AC-Name: '%s')",
+                  mac->ether_addr_octet[0],
+                  mac->ether_addr_octet[1],
+                  mac->ether_addr_octet[2],
+                  mac->ether_addr_octet[3],
+                  mac->ether_addr_octet[4],
+                  mac->ether_addr_octet[5],
+                  ppp->tags.service_name ? : "",
+                  ppp->tags.ac_name ? : "");
+
+                memcpy(&ppp->peer_mac, mac, ETH_ALEN);
+
+                r = pppoe_open_pppoe_socket(ppp);
+                if (r < 0) {
+                        log_warning("PPPoE: could not open socket");
+                        return r;
+                }
+
+                r = pppoe_send_request(ppp);
+                if (r < 0)
+                        return 0;
+
+                ppp->state = PPPOE_STATE_REQUESTING;
+
+                break;
+        case PPPOE_STATE_REQUESTING:
+                if (packet->code != PADS_CODE)
+                        return 0;
+
+                if (ppp->tags.host_uniq_len != sizeof(ppp->host_uniq) ||
+                    memcmp(ppp->tags.host_uniq, &ppp->host_uniq,
+                           sizeof(ppp->host_uniq)) != 0)
+                        return 0;
+
+                if (memcmp(&ppp->peer_mac, mac, ETH_ALEN) != 0)
+                        return 0;
+
+                ppp->session_id = packet->sid;
+
+                log_debug("PPPoE: got CONFIRMATION (Session ID: %"PRIu16")",
+                          be16toh(ppp->session_id));
+
+                r = pppoe_connect_pppoe_socket(ppp);
+                if (r < 0) {
+                        log_warning("PPPoE: could not connect socket");
+                        return r;
+                }
+
+                ppp->state = PPPOE_STATE_RUNNING;
+
+                ppp->timeout = sd_event_source_unref(ppp->timeout);
+                assert(ppp->cb);
+                ppp->cb(ppp, PPPOE_EVENT_RUNNING, ppp->userdata);
+
+                break;
+        case PPPOE_STATE_RUNNING:
+                if (packet->code != PADT_CODE)
+                        return 0;
+
+                if (memcmp(&ppp->peer_mac, mac, ETH_ALEN) != 0)
+                        return 0;
+
+                if (ppp->session_id != packet->sid)
+                        return 0;
+
+                log_debug("PPPoE: got TERMINATE");
+
+                ppp->state = PPPOE_STATE_STOPPED;
+
+                assert(ppp->cb);
+                ppp->cb(ppp, PPPOE_EVENT_STOPPED, ppp->userdata);
+
+                break;
+        case PPPOE_STATE_STOPPED:
+                break;
+        default:
+                assert_not_reached("PPPoE: invalid state when receiving message");
+        }
+
+        return 0;
+}
+
+static int pppoe_receive_message(sd_event_source *s, int fd,
+                                 uint32_t revents, void *userdata) {
+        sd_pppoe *ppp = userdata;
+        _cleanup_free_ struct pppoe_hdr *packet = NULL;
+        union sockaddr_union link = {};
+        socklen_t addrlen = sizeof(link);
+        int buflen = 0, len, r;
+
+        assert(ppp);
+        assert(fd != -1);
+
+        r = ioctl(fd, FIONREAD, &buflen);
+        if (r < 0)
+                return r;
+
+        if (buflen < 0)
+                /* this can't be right */
+                return -EIO;
+
+        packet = malloc0(buflen);
+        if (!packet)
+                return -ENOMEM;
+
+        len = recvfrom(fd, packet, buflen, 0,
+                       &link.sa, &addrlen);
+        if (len < 0) {
+                log_warning("PPPoE: colud not receive message from raw socket: %s",
+                          strerror(-r));
+                return 0;
+        } else if ((size_t)len < sizeof(struct pppoe_hdr))
+                return 0;
+        else if ((size_t)len != sizeof(struct pppoe_hdr) + PPPOE_PACKET_LENGTH(packet))
+                return 0;
+
+        if (link.ll.sll_halen != ETH_ALEN)
+                /* not ethernet? */
+                return 0;
+
+        r = pppoe_handle_message(ppp, packet, (struct ether_addr*)&link.ll.sll_addr);
+        if (r < 0)
+                return r;
+
+        return 1;
+}
+
+int sd_pppoe_start(sd_pppoe *ppp) {
+        union sockaddr_union link = {
+                .ll = {
+                        .sll_family = AF_PACKET,
+                        .sll_protocol = htons(ETH_P_PPP_DISC),
+                },
+        };
+        _cleanup_close_ int s = -1;
+        _cleanup_event_source_unref_ sd_event_source *io = NULL;
+        int r;
+
+        assert_return(ppp, -EINVAL);
+        assert_return(ppp->fd == -1, -EBUSY);
+        assert_return(!ppp->io, -EBUSY);
+        assert_return(ppp->ifindex > 0, -EUNATCH);
+        assert_return(ppp->ifname, -EUNATCH);
+        assert_return(ppp->event, -EUNATCH);
+        assert_return(ppp->cb, -EUNATCH);
+
+        s = socket(AF_PACKET, SOCK_DGRAM | SOCK_CLOEXEC | SOCK_NONBLOCK, 0);
+        if (s < 0)
+                return -errno;
+
+        link.ll.sll_ifindex = ppp->ifindex;
+
+        r = bind(s, &link.sa, sizeof(link.ll));
+        if (r < 0)
+                return r;
+
+        r = sd_event_add_io(ppp->event, &io,
+                            s, EPOLLIN, pppoe_receive_message,
+                            ppp);
+        if (r < 0)
+                return r;
+
+        r = sd_event_source_set_priority(io, ppp->event_priority);
+        if (r < 0)
+                return r;
+
+        ppp->fd = s;
+        s = -1;
+        ppp->io = io;
+        io = NULL;
+
+        r = pppoe_send_initiation(ppp);
+        if (r < 0)
+                return r;
+
+        ppp->state = PPPOE_STATE_INITIALIZING;
+
+        return 0;
+}
+
+int sd_pppoe_stop(sd_pppoe *ppp) {
+        assert_return(ppp, -EINVAL);
+
+        if (ppp->state == PPPOE_STATE_RUNNING)
+                pppoe_send_terminate(ppp);
+
+        ppp->io = sd_event_source_unref(ppp->io);
+        ppp->timeout = sd_event_source_unref(ppp->timeout);
+        ppp->fd = asynchronous_close(ppp->fd);
+        ppp->pppoe_fd = asynchronous_close(ppp->pppoe_fd);
+
+        return 0;
+}