Use netlink to detect going online

Integrates libnl to detect adding routes. When a route is added, the
offline status of all back ends is reset. This patch adds no heuristics
to detect whether back end went offline.

Fixes: #456

1 files changed, 406 insertions, 0 deletions

diff --git a/src/monitor/monitor_netlink.c b/src/monitor/monitor_netlink.c
new file mode 100644
index 00000000..da4b673d
--- /dev/null
+++ b/src/monitor/monitor_netlink.c
@@ -0,0 +1,406 @@
+/*
+   SSSD - Service monitor - netlink support
+
+   Authors:
+       Jakub Hrozek <jhrozek@redhat.com>
+       Parts of this code were borrowed from NetworkManager
+
+   Copyright (C) 2010 Red Hat
+
+   This program is free software; you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 3 of the License, or
+   (at your option) any later version.
+
+   This program 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 General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.
+*/
+
+#include <talloc.h>
+#include <tevent.h>
+#include <sys/types.h>
+#define __USE_GNU /* needed for struct ucred */
+#include <sys/socket.h>
+#include <unistd.h>
+#include <fcntl.h>
+
+#include "monitor/monitor.h"
+#include "util/util.h"
+
+#ifdef HAVE_LIBNL
+#include <linux/if.h>
+#include <linux/socket.h>
+#include <linux/rtnetlink.h>
+#include <netlink/netlink.h>
+#include <netlink/utils.h>
+#include <netlink/route/addr.h>
+#include <netlink/route/link.h>
+#include <netlink/route/rtnl.h>
+#include <netlink/handlers.h>
+#endif
+
+/* Linux header file confusion causes this to be undefined. */
+#ifndef SOL_NETLINK
+#define SOL_NETLINK 270
+#endif
+
+#ifdef HAVE_LIBNL_OLDER_THAN_1_1
+#define nlw_get_fd nl_handle_get_fd
+#define nlw_recvmsgs_default nl_recvmsgs_def
+#define nlw_get_pid nl_handle_get_pid
+#define nlw_object_match nl_object_match
+#define NLW_OK NL_PROCEED
+#define OBJ_CAST(ptr)           ((struct nl_object *) (ptr))
+#else
+#define nlw_get_fd nl_socket_get_fd
+#define nlw_recvmsgs_default nl_recvmsgs_default
+#define nlw_get_pid nl_socket_get_local_port
+#define nlw_object_match nl_object_match_filter
+#define NLW_OK NL_OK
+#endif
+
+struct netlink_ctx {
+#ifdef HAVE_LIBNL
+    struct nl_handle *nlh;
+#endif
+    struct tevent_fd *tefd;
+
+    network_change_cb change_cb;
+    void *cb_data;
+};
+
+#ifdef HAVE_LIBNL
+static int netlink_ctx_destructor(void *ptr)
+{
+    struct netlink_ctx *nlctx;
+    nlctx = talloc_get_type(ptr, struct netlink_ctx);
+
+    nl_handle_destroy(nlctx->nlh);
+    return 0;
+}
+
+/*******************************************************************
+ * Wrappers for different capabilities of different libnl versions
+ *******************************************************************/
+
+static bool nlw_accept_message(struct nl_handle *nlh,
+                               const struct sockaddr_nl *snl,
+                               struct nlmsghdr *hdr)
+{
+    bool accept_msg = false;
+    uint32_t local_port;
+
+    if (snl == NULL) {
+        DEBUG(3, ("Malformed message, skipping\n"));
+        return false;
+    }
+
+    /* Accept any messages from the kernel */
+    if (hdr->nlmsg_pid == 0 || snl->nl_pid == 0) {
+        accept_msg = true;
+    }
+
+    /* And any multicast message directed to our netlink PID, since multicast
+     * currently requires CAP_ADMIN to use.
+     */
+    local_port = nlw_get_pid(nlh);
+    if ((hdr->nlmsg_pid == local_port) && snl->nl_groups) {
+        accept_msg = true;
+    }
+
+    if (accept_msg == false) {
+        DEBUG(9, ("ignoring netlink message from PID %d",
+                  hdr->nlmsg_pid));
+    }
+
+    return accept_msg;
+}
+
+static bool nlw_is_link_object(struct nl_object *obj)
+{
+    bool is_link_object = true;
+    struct rtnl_link *filter;
+
+    filter = rtnl_link_alloc();
+    if (!filter) {
+        DEBUG(0, ("Allocation error!\n"));
+        is_link_object = false;
+    }
+
+    /* Ensure it's a link object */
+    if (!nlw_object_match(obj, OBJ_CAST(filter))) {
+        DEBUG(2, ("Not a link object\n"));
+        is_link_object = false;
+    }
+
+    rtnl_link_put(filter);
+    return is_link_object;
+}
+
+static int nlw_enable_passcred(struct nl_handle *nlh)
+{
+#ifndef HAVE_NL_SET_PASSCRED
+    return EOK;                      /* not available in this version */
+#else
+    return nl_set_passcred(nlh, 1);  /* 1 = enabled */
+#endif
+}
+
+static int nlw_group_subscribe(struct nl_handle *nlh)
+{
+    int ret;
+
+#ifdef HAVE_NL_SOCKET_ADD_MEMBERSHIP
+    ret = nl_socket_add_membership(nlh, RTNLGRP_LINK);
+    if (ret != 0) {
+        DEBUG(1, ("Unable to add membership: %s\n", nl_geterror()));
+        return ret;
+    }
+#else
+     int nlfd = nlw_get_fd(nlh);
+     int group = RTNLGRP_LINK;
+
+     errno = 0;
+     ret = setsockopt(nlfd, SOL_NETLINK, NETLINK_ADD_MEMBERSHIP,
+                      &group, sizeof(group));
+     if (ret < 0) {
+         ret = errno;
+         DEBUG(1, ("setsockopt failed (%d): %s\n", ret, strerror(ret)));
+         return ret;
+     }
+#endif
+
+     return 0;
+}
+
+/*******************************************************************
+ * Callbacks for validating and receiving messages
+ *******************************************************************/
+
+#ifdef HAVE_LIBNL_OLDER_THAN_1_1
+static int event_msg_recv(struct sockaddr_nl *nla, struct nlmsghdr *hdr,
+                          void *arg)
+{
+    struct netlink_ctx *ctx = (struct netlink_ctx *) arg;
+
+    if (!nlw_accept_message(ctx->nlh, nla, hdr)) {
+        return NL_SKIP;
+    }
+
+    return NLW_OK;
+}
+#else
+static int event_msg_recv(struct nl_msg *msg, void *arg)
+{
+    struct netlink_ctx *ctx = (struct netlink_ctx *) arg;
+    struct nlmsghdr *hdr;
+    const struct sockaddr_nl *snl;
+    struct ucred *creds;
+
+    creds = nlmsg_get_creds(msg);
+    if (!creds || creds->uid != 0) {
+        DEBUG(9, ("Ignoring netlink message from UID %d",
+                  creds ? creds->uid : -1));
+        return NL_SKIP;
+    }
+
+    hdr = nlmsg_hdr(msg);
+    snl = nlmsg_get_src(msg);
+
+    if (!nlw_accept_message(ctx->nlh, snl, hdr)) {
+        return NL_SKIP;
+    }
+
+    return NLW_OK;
+}
+#endif
+
+static void link_msg_handler(struct nl_object *obj, void *arg);
+
+#ifdef HAVE_LIBNL_OLDER_THAN_1_1
+static int event_msg_ready(struct sockaddr_nl *nla, struct nlmsghdr *hdr,
+                           void *arg)
+{
+    nl_msg_parse(hdr, &link_msg_handler, arg);
+    return NLW_OK;
+}
+#else
+static int event_msg_ready(struct nl_msg *msg, void *arg)
+{
+    nl_msg_parse(msg, &link_msg_handler, arg);
+    return NLW_OK;
+}
+#endif
+
+static int nlw_set_callbacks(struct nl_handle *nlh, void *data)
+{
+    int ret = EIO;
+
+#ifndef HAVE_NL_SOCKET_MODIFY_CB
+    struct nl_cb *cb = nl_handle_get_cb(nlh);
+    ret = nl_cb_set(cb, NL_CB_MSG_IN, NL_CB_CUSTOM, event_msg_recv, data);
+#else
+    ret = nl_socket_modify_cb(nlh, NL_CB_MSG_IN, NL_CB_CUSTOM, event_msg_recv, data);
+#endif
+    if (ret != 0) {
+        DEBUG(1, ("Unable to set validation callback\n"));
+        return ret;
+    }
+
+#ifndef HAVE_NL_SOCKET_MODIFY_CB
+    ret = nl_cb_set(cb, NL_CB_VALID, NL_CB_CUSTOM, event_msg_ready, data);
+#else
+    ret = nl_socket_modify_cb(nlh, NL_CB_VALID, NL_CB_CUSTOM, event_msg_ready, data);
+#endif
+    if (ret != 0) {
+        DEBUG(1, ("Unable to set receive callback\n"));
+        return ret;
+    }
+
+    return ret;
+}
+
+static void link_msg_handler(struct nl_object *obj, void *arg)
+{
+    struct netlink_ctx *ctx = (struct netlink_ctx *) arg;
+    struct rtnl_link *link_obj;
+    int flags;
+    int ifidx;
+
+    if (!nlw_is_link_object(obj)) return;
+
+    link_obj = (struct rtnl_link *) obj;
+    flags = rtnl_link_get_flags(link_obj);
+    ifidx = rtnl_link_get_ifindex(link_obj);
+
+    DEBUG(8, ("netlink link message: iface idx %d flags 0x%X\n", ifidx, flags));
+
+    /* IFF_LOWER_UP is the indicator of carrier status */
+    if (flags & IFF_LOWER_UP) {
+        ctx->change_cb(NL_ROUTE_UP, ctx->cb_data);
+    } else {
+        ctx->change_cb(NL_ROUTE_DOWN, ctx->cb_data);
+    }
+}
+
+static void netlink_fd_handler(struct tevent_context *ev, struct tevent_fd *fde,
+                               uint16_t flags, void *data)
+{
+    struct netlink_ctx *nlctx = talloc_get_type(data, struct netlink_ctx);
+    int ret;
+
+    if (!nlctx || !nlctx->nlh) {
+        DEBUG(1, ("Invalid netlink handle, this is most likely a bug!\n"));
+        return;
+    }
+
+    ret = nlw_recvmsgs_default(nlctx->nlh);
+    if (ret != EOK) {
+        DEBUG(1, ("Error while reading from netlink fd\n"));
+        return;
+    }
+}
+
+/*******************************************************************
+ * Set up the netlink library
+ *******************************************************************/
+
+int setup_netlink(TALLOC_CTX *mem_ctx, struct tevent_context *ev,
+                  network_change_cb change_cb, void *cb_data,
+                  struct netlink_ctx **_nlctx)
+{
+    struct netlink_ctx *nlctx;
+    int ret;
+    int nlfd;
+    unsigned flags;
+
+    nlctx = talloc_zero(mem_ctx, struct netlink_ctx);
+    if (!nlctx) return ENOMEM;
+    talloc_set_destructor((TALLOC_CTX *) nlctx, netlink_ctx_destructor);
+
+    nlctx->change_cb = change_cb;
+    nlctx->cb_data   = cb_data;
+
+    /* allocate the libnl handle and register the default filter set */
+    nlctx->nlh = nl_handle_alloc();
+    if (!nlctx->nlh) {
+        DEBUG(1, (("unable to allocate netlink handle: %s"),
+                   nl_geterror()));
+        ret = ENOMEM;
+        goto fail;
+    }
+
+    /* Register our custom message validation filter */
+    ret = nlw_set_callbacks(nlctx->nlh, nlctx);
+    if (ret != 0) {
+        DEBUG(1, ("Unable to set callbacks\n"));
+        ret = EIO;
+        goto fail;
+    }
+
+    /* Try to start talking to netlink */
+    ret = nl_connect(nlctx->nlh, NETLINK_ROUTE);
+    if (ret != 0) {
+        DEBUG(1, ("Unable to connect to netlink: %s\n", nl_geterror()));
+        ret = EIO;
+        goto fail;
+    }
+
+    ret = nlw_enable_passcred(nlctx->nlh);
+    if (ret != 0) {
+        DEBUG(1, ("Cannot enable credential passing: %s\n", nl_geterror()));
+        ret = EIO;
+        goto fail;
+    }
+
+    /* Subscribe to the LINK group for internal carrier signals */
+    ret = nlw_group_subscribe(nlctx->nlh);
+    if (ret != 0) {
+        DEBUG(1, ("Unable to subscribe to netlink monitor\n"));
+        ret = EIO;
+        goto fail;
+    }
+
+    nl_disable_sequence_check(nlctx->nlh);
+
+    nlfd = nlw_get_fd(nlctx->nlh);
+    flags = fcntl(nlfd, F_GETFL, 0);
+
+    errno = 0;
+    ret = fcntl(nlfd, F_SETFL, flags | O_NONBLOCK);
+    if (ret < 0) {
+        ret = errno;
+        DEBUG(1, ("Cannot set the netlink fd to nonblocking\n"));
+        goto fail;
+    }
+
+    nlctx->tefd = tevent_add_fd(ev, nlctx, nlfd, TEVENT_FD_READ,
+                                netlink_fd_handler, nlctx);
+    if (nlctx->tefd == NULL) {
+        DEBUG(1, ("tevent_add_fd() failed\n"));
+        ret = EIO;
+        goto fail;
+    }
+
+    *_nlctx = nlctx;
+    return EOK;
+
+fail:
+    talloc_free(nlctx);
+    return ret;
+}
+
+#else       /* HAVE_LIBNL not defined */
+int setup_netlink(TALLOC_CTX *mem_ctx, struct tevent_context *ev,
+                  network_change_cb change_cb, void *cb_data,
+                  struct netlink_ctx **_nlctx)
+{
+    if (nlctx) *nlctx = NULL;
+    return EOK;
+}
+#endif