Systemd/src/libsystemd-rtnl/rtnl-message.c

/*-*- Mode: C; c-basic-offset: 8; indent-tabs-mode: nil -*-*/

/***
  This file is part of systemd.

  Copyright 2013 Tom Gundersen <teg@jklm.no>

  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/>.
***/

#include <netinet/in.h>
#include <netinet/ether.h>
#include <stdbool.h>
#include <unistd.h>

#include "util.h"
#include "refcnt.h"

#include "sd-rtnl.h"
#include "rtnl-internal.h"

struct sd_rtnl_message {
        RefCount n_ref;

        struct nlmsghdr *hdr;

        struct rtattr *next_rta;
        size_t remaining_size;

        bool sealed:1;
};

static int message_new(sd_rtnl_message **ret, size_t initial_size) {
        sd_rtnl_message *m;

        assert_return(ret, -EINVAL);
        assert_return(initial_size >= sizeof(struct nlmsghdr), -EINVAL);

        m = new0(sd_rtnl_message, 1);
        if (!m)
                return -ENOMEM;

        m->hdr = malloc0(initial_size);
        if (!m->hdr) {
                free(m);
                return -ENOMEM;
        }

        m->n_ref = REFCNT_INIT;

        m->hdr->nlmsg_flags = NLM_F_REQUEST | NLM_F_ACK;
        m->sealed = false;

        *ret = m;

        return 0;
}

int sd_rtnl_message_link_new(uint16_t nlmsg_type, int index, unsigned int type, unsigned int flags, sd_rtnl_message **ret) {
        struct ifinfomsg *ifi;
        int r;

        assert_return(nlmsg_type == RTM_NEWLINK || nlmsg_type == RTM_DELLINK || nlmsg_type == RTM_GETLINK, -EINVAL);
        assert_return(index > 0, -EINVAL);
        assert_return(ret, -EINVAL);

        r = message_new(ret, NLMSG_SPACE(sizeof(struct ifinfomsg)));
        if (r < 0)
                return r;

        (*ret)->hdr->nlmsg_len = NLMSG_LENGTH(sizeof(struct ifinfomsg));
        (*ret)->hdr->nlmsg_type = nlmsg_type;

        ifi = NLMSG_DATA((*ret)->hdr);

        ifi->ifi_family = AF_UNSPEC;
        ifi->ifi_index = index;
        ifi->ifi_type = type;
        ifi->ifi_flags = flags;
        ifi->ifi_change = 0xffffffff;

        return 0;
}

int sd_rtnl_message_addr_new(uint16_t nlmsg_type, int index, unsigned char family, unsigned char prefixlen, unsigned char flags, unsigned char scope, sd_rtnl_message **ret) {
        struct ifaddrmsg *ifa;
        int r;

        assert_return(nlmsg_type == RTM_NEWADDR || nlmsg_type == RTM_DELADDR || nlmsg_type == RTM_GETADDR, -EINVAL);
        assert_return(index > 0, -EINVAL);
        assert_return(ret, -EINVAL);

        r = message_new(ret, NLMSG_SPACE(sizeof(struct ifaddrmsg)));
        if (r < 0)
                return r;

        (*ret)->hdr->nlmsg_len = NLMSG_LENGTH(sizeof(struct ifaddrmsg));
        (*ret)->hdr->nlmsg_type = nlmsg_type;

        ifa = NLMSG_DATA((*ret)->hdr);

        ifa->ifa_family = family;
        ifa->ifa_prefixlen = prefixlen;
        ifa->ifa_flags = flags;
        ifa->ifa_scope = scope;
        ifa->ifa_index = index;

        return 0;
}

sd_rtnl_message *sd_rtnl_message_ref(sd_rtnl_message *m) {
        if (m)
                assert_se(REFCNT_INC(m->n_ref) >= 2);

        return m;
}

sd_rtnl_message *sd_rtnl_message_unref(sd_rtnl_message *m) {
        if (m && REFCNT_DEC(m->n_ref) <= 0) {
                free(m->hdr);
                free(m);
        }

        return NULL;
}

int sd_rtnl_message_get_type(sd_rtnl_message *m, uint16_t *type) {
        assert_return(m, -EINVAL);
        assert_return(type, -EINVAL);

        *type = m->hdr->nlmsg_type;

        return 0;
}

/* If successful the updated message will be correctly aligned, if unsuccessful the old message is
   untouched */
static int add_rtattr(sd_rtnl_message *m, unsigned short type, const void *data, size_t data_length) {
        uint32_t rta_length, message_length;
        struct nlmsghdr *new_hdr;
        struct rtattr *rta;

        assert_return(m, -EINVAL);
        assert_return(m->hdr, -EINVAL);
        assert_return(NLMSG_ALIGN(m->hdr->nlmsg_len) == m->hdr->nlmsg_len, -EINVAL);
        assert_return(data, -EINVAL);
        assert_return(data_length > 0, -EINVAL);

        /* get the size of the new rta attribute (without padding at the end) */
        rta_length = RTA_LENGTH(data_length);
        /* get the new message size (with padding between the old message and the new attrib,
         * but no padding after)
         */
        message_length = m->hdr->nlmsg_len + RTA_ALIGN(rta_length);

        /* realloc to fit the new attribute */
        new_hdr = realloc(m->hdr, message_length);
        if (!new_hdr)
                return -ENOMEM;
        m->hdr = new_hdr;

        /* get pointer to the attribute we are about to add */
        rta = (struct rtattr *) ((uint8_t *) m->hdr + m->hdr->nlmsg_len);
        /* update message size */
        m->hdr->nlmsg_len = message_length;

        /* fill in the attribute */
        rta->rta_type = type;
        rta->rta_len = rta_length;
        /* we don't deal with the case where the user lies about the type and gives us
         * too little data (so don't do that)
         */
        memcpy(RTA_DATA(rta), data, data_length);

        return 0;
}

int sd_rtnl_message_append(sd_rtnl_message *m, unsigned short type, const void *data) {
        uint16_t rtm_type;
        struct ifaddrmsg *ifa;

        assert_return(m, -EINVAL);
        assert_return(data, -EINVAL);

        sd_rtnl_message_get_type(m, &rtm_type);

        switch (rtm_type) {
                case RTM_NEWLINK:
                case RTM_DELLINK:
                case RTM_GETLINK:
                        switch (type) {
                                case IFLA_IFNAME:
                                case IFLA_QDISC:
                                        return add_rtattr(m, type, data, strlen(data) + 1);
                                case IFLA_MTU:
                                        return add_rtattr(m, type, data, sizeof(unsigned int));
                                case IFLA_LINK:
                                        return add_rtattr(m, type, data, sizeof(int));
                                case IFLA_STATS:
                                        return add_rtattr(m, type, data, sizeof(struct rtnl_link_stats));
                                case IFLA_ADDRESS:
                                case IFLA_BROADCAST:
                                        return add_rtattr(m, type, data, ETH_ALEN);
                                default:
                                        return -ENOTSUP;
                        }
                case RTM_NEWADDR:
                case RTM_DELADDR:
                case RTM_GETADDR:
                        switch (type) {
                                case IFA_LABEL:
                                        return add_rtattr(m, type, data, strlen(data) + 1);
                                case IFA_ADDRESS:
                                case IFA_LOCAL:
                                case IFA_BROADCAST:
                                case IFA_ANYCAST:
                                        ifa = NLMSG_DATA(m->hdr);
                                        switch (ifa->ifa_family) {
                                                case AF_INET:
                                                        return add_rtattr(m, type, data, sizeof(struct in_addr));
                                                case AF_INET6:
                                                        return add_rtattr(m, type, data, sizeof(struct in6_addr));
                                                default:
                                                        return -EINVAL;
                                        }
                                default:
                                        return -ENOTSUP;
                        }
                default:
                        return -ENOTSUP;
        }
}

static int message_read(sd_rtnl_message *m, unsigned short *type, void **data) {
        assert_return(m, -EINVAL);
        assert_return(data, -EINVAL);

        if (!RTA_OK(m->next_rta, m->remaining_size))
                return 0;

        *data = RTA_DATA(m->next_rta);
        *type = m->next_rta->rta_type;

        m->next_rta = RTA_NEXT(m->next_rta, m->remaining_size);

        return 1;
}

int sd_rtnl_message_read(sd_rtnl_message *m, unsigned short *type, void **data) {
        uint16_t rtm_type;

        assert_return(m, -EINVAL);
        assert_return(data, -EINVAL);

        sd_rtnl_message_get_type(m, &rtm_type);

        switch (rtm_type) {
                case RTM_NEWLINK:
                case RTM_DELLINK:
                case RTM_GETLINK:
                        if (!m->next_rta) {
                                struct ifinfomsg *ifi = NLMSG_DATA(m->hdr);

                                m->next_rta = IFLA_RTA(ifi);
                                m->remaining_size = IFLA_PAYLOAD(m->hdr);
                        }
                        break;;
                case RTM_NEWADDR:
                case RTM_DELADDR:
                case RTM_GETADDR:
                        if (!m->next_rta) {
                                struct ifaddrmsg *ifa = NLMSG_DATA(m->hdr);

                                m->next_rta = IFA_RTA(ifa);
                                m->remaining_size = IFLA_PAYLOAD(m->hdr);
                        }
                        break;;
                default:
                        return -ENOTSUP;
        }

        return message_read(m, type, data);
}

int message_get_serial(sd_rtnl_message *m) {
        assert(m);

        return m->hdr->nlmsg_seq;
}

int message_get_errno(sd_rtnl_message *m) {
        struct nlmsgerr *err;

        assert(m);

        if (m->hdr->nlmsg_type != NLMSG_ERROR)
                return 0;

        err = NLMSG_DATA(m->hdr);

        return err->error;
}

int message_seal(sd_rtnl *nl, sd_rtnl_message *m) {
        if (m->sealed)
                return -EPERM;

        m->hdr->nlmsg_seq = nl->serial++;
        m->sealed = true;

        return 0;
}

static int message_receive_need(sd_rtnl *rtnl, size_t *need) {
        assert_return(rtnl, -EINVAL);
        assert_return(need, -EINVAL);

        /* ioctl(rtnl->fd, FIONREAD, &need)
           Does not appear to work on netlink sockets. libnl uses
           MSG_PEEK instead. I don't know if that is worth the
           extra roundtrip.

           For now we simply use the maximum message size the kernel
           may use (NLMSG_GOODSIZE), and then realloc to the actual
           size after reading the message (hence avoiding huge memory
           usage in case many small messages are kept around) */
        *need = page_size();
        if (*need > 8192UL)
                *need = 8192UL;

        return 0;
}

/* returns the number of bytes sent, or a negative error code */
int socket_write_message(sd_rtnl *nl, sd_rtnl_message *m) {
        union {
                struct sockaddr sa;
                struct sockaddr_nl nl;
        } addr = {
                .nl.nl_family = AF_NETLINK,
        };
        ssize_t k;

        assert_return(nl, -EINVAL);
        assert_return(m, -EINVAL);

        k = sendto(nl->fd, m->hdr, m->hdr->nlmsg_len,
                        0, &addr.sa, sizeof(addr));
        if (k < 0)
                return (errno == EAGAIN) ? 0 : -errno;

        return k;
}

/* On success, the number of bytes received is returned and *ret points to the received message
 * which has a valid header and the correct size.
 * If nothing useful was received 0 is returned.
 * On failure, a negative error code is returned.
 */
int socket_read_message(sd_rtnl *nl, sd_rtnl_message **ret) {
        sd_rtnl_message *m;
        union {
                struct sockaddr sa;
                struct sockaddr_nl nl;
        } addr;
        socklen_t addr_len;
        int r;
        ssize_t k;
        size_t need;

        assert_return(nl, -EINVAL);
        assert_return(ret, -EINVAL);

        r = message_receive_need(nl, &need);
        if (r < 0)
                return r;

        r = message_new(&m, need);
        if (r < 0)
                return r;

        addr_len = sizeof(addr);

        k = recvfrom(nl->fd, m->hdr, need,
                        0, &addr.sa, &addr_len);
        if (k < 0)
                k = (errno == EAGAIN) ? 0 : -errno; /* no data */
        else if (k == 0)
                k = -ECONNRESET; /* connection was closed by the kernel */
        else if (addr_len != sizeof(addr.nl) ||
                        addr.nl.nl_family != AF_NETLINK)
                k = -EIO; /* not a netlink message */
        else if (addr.nl.nl_pid != 0)
                k = 0; /* not from the kernel */
        else if ((size_t) k < sizeof(struct nlmsghdr) ||
                        (size_t) k < m->hdr->nlmsg_len)
                k = -EIO; /* too small (we do accept too big though) */
        else if (m->hdr->nlmsg_pid != nl->sockaddr.nl.nl_pid)
                k = 0; /* not for us */

        if (k > 0)
                switch (m->hdr->nlmsg_type) {
                        /* check that the size matches the message type */
                        case NLMSG_ERROR:
                                if (m->hdr->nlmsg_len < NLMSG_LENGTH(sizeof(struct nlmsgerr)))
                                        k = -EIO;
                                break;;
                        case RTM_NEWLINK:
                        case RTM_DELLINK:
                        case RTM_GETLINK:
                                if (m->hdr->nlmsg_len < NLMSG_LENGTH(sizeof(struct ifinfomsg)))
                                        k = -EIO;
                                break;;
                        case RTM_NEWADDR:
                        case RTM_DELADDR:
                        case RTM_GETADDR:
                                if (m->hdr->nlmsg_len < NLMSG_LENGTH(sizeof(struct ifaddrmsg)))
                                        k = -EIO;
                                break;;
                        case NLMSG_NOOP:
                                k = 0;
                                break;;
                        default:
                                k = 0; /* ignoring message of unknown type */
                }

        if (k <= 0)
                sd_rtnl_message_unref(m);
        else {
                /* we probably allocated way too much memory, give it back */
                m->hdr = realloc(m->hdr, m->hdr->nlmsg_len);
                *ret = m;
        }

        return k;
}