sd-radv: Receive Router Solicitations

Receive Router Solicitations and send a unicast Router Advertisment
in response. Refactor ICMPv6 packet handling code so that the common
ICMPv6 validation parts are reused between the existing router
discovery and the new functionality adding reception of Router
Solicitation messages.

src/libsystemd-network/icmp6-util.c

@@ -32,6 +32,7 @@
 #include "fd-util.h"
 #include "icmp6-util.h"
 #include "socket-util.h"
+#include "in-addr-util.h"
 
 #define IN6ADDR_ALL_ROUTERS_MULTICAST_INIT \
         { { { 0xff, 0x02, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, \
@@ -164,3 +165,74 @@ int icmp6_send_router_solicitation(int s, const struct ether_addr *ether_addr) {
 
         return 0;
 }
+
+int icmp6_receive(int fd, void *buffer, size_t size, struct in6_addr *dst,
+                  triple_timestamp *timestamp) {
+        union {
+                struct cmsghdr cmsghdr;
+                uint8_t buf[CMSG_SPACE(sizeof(int)) + /* ttl */
+                            CMSG_SPACE(sizeof(struct timeval))];
+        } control = {};
+        struct iovec iov = {};
+        union sockaddr_union sa = {};
+        struct msghdr msg = {
+                .msg_name = &sa.sa,
+                .msg_namelen = sizeof(sa),
+                .msg_iov = &iov,
+                .msg_iovlen = 1,
+                .msg_control = &control,
+                .msg_controllen = sizeof(control),
+        };
+        struct cmsghdr *cmsg;
+        ssize_t len;
+
+        iov.iov_base = buffer;
+        iov.iov_len = size;
+
+        len = recvmsg(fd, &msg, MSG_DONTWAIT);
+        if (len < 0) {
+                if (errno == EAGAIN || errno == EINTR)
+                        return 0;
+
+                return -errno;
+        }
+
+        if ((size_t) len != size)
+                return -EINVAL;
+
+        if (msg.msg_namelen == sizeof(struct sockaddr_in6) &&
+            sa.in6.sin6_family == AF_INET6)  {
+
+                *dst = sa.in6.sin6_addr;
+                if (in_addr_is_link_local(AF_INET6, (union in_addr_union*) dst) <= 0)
+                        return -EADDRNOTAVAIL;
+
+        } else if (msg.msg_namelen > 0)
+                return -EPFNOSUPPORT;
+
+        /* namelen == 0 only happens when running the test-suite over a socketpair */
+
+        assert(!(msg.msg_flags & MSG_CTRUNC));
+        assert(!(msg.msg_flags & MSG_TRUNC));
+
+        CMSG_FOREACH(cmsg, &msg) {
+                if (cmsg->cmsg_level == SOL_IPV6 &&
+                    cmsg->cmsg_type == IPV6_HOPLIMIT &&
+                    cmsg->cmsg_len == CMSG_LEN(sizeof(int))) {
+                        int hops = *(int*) CMSG_DATA(cmsg);
+
+                        if (hops != 255)
+                                return -EMULTIHOP;
+                }
+
+                if (cmsg->cmsg_level == SOL_SOCKET &&
+                    cmsg->cmsg_type == SO_TIMESTAMP &&
+                    cmsg->cmsg_len == CMSG_LEN(sizeof(struct timeval)))
+                        triple_timestamp_from_realtime(timestamp, timeval_load((struct timeval*) CMSG_DATA(cmsg)));
+        }
+
+        if (!triple_timestamp_is_set(timestamp))
+                triple_timestamp_get(timestamp);
+
+        return 0;
+}

src/libsystemd-network/icmp6-util.h

@@ -21,6 +21,8 @@
 
 #include <net/ethernet.h>
 
+#include "time-util.h"
+
 #define IN6ADDR_ALL_ROUTERS_MULTICAST_INIT \
         { { { 0xff, 0x02, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, \
               0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x02 } } }
@@ -32,3 +34,5 @@
 int icmp6_bind_router_solicitation(int index);
 int icmp6_bind_router_advertisement(int index);
 int icmp6_send_router_solicitation(int s, const struct ether_addr *ether_addr);
+int icmp6_receive(int fd, void *buffer, size_t size, struct in6_addr *dst,
+                  triple_timestamp *timestamp);

src/libsystemd-network/radv-internal.h

@@ -58,6 +58,7 @@ struct sd_radv {
 
         int fd;
         unsigned ra_sent;
+        sd_event_source *recv_event_source;
         sd_event_source *timeout_event_source;
 
         unsigned n_prefixes;

src/libsystemd-network/sd-ndisc.c

@@ -222,23 +222,9 @@ static int ndisc_handle_datagram(sd_ndisc *nd, sd_ndisc_router *rt) {
 static int ndisc_recv(sd_event_source *s, int fd, uint32_t revents, void *userdata) {
         _cleanup_(sd_ndisc_router_unrefp) sd_ndisc_router *rt = NULL;
         sd_ndisc *nd = userdata;
-        union {
-                struct cmsghdr cmsghdr;
-                uint8_t buf[CMSG_SPACE(sizeof(int)) + /* ttl */
-                            CMSG_SPACE(sizeof(struct timeval))];
-        } control = {};
-        struct iovec iov = {};
-        union sockaddr_union sa = {};
-        struct msghdr msg = {
-                .msg_name = &sa.sa,
-                .msg_namelen = sizeof(sa),
-                .msg_iov = &iov,
-                .msg_iovlen = 1,
-                .msg_control = &control,
-                .msg_controllen = sizeof(control),
-        };
-        struct cmsghdr *cmsg;
-        ssize_t len, buflen;
+        ssize_t buflen;
+        int r;
+        _cleanup_free_ char *addr = NULL;
 
         assert(s);
         assert(nd);
@@ -252,66 +238,27 @@ static int ndisc_recv(sd_event_source *s, int fd, uint32_t revents, void *userda
         if (!rt)
                 return -ENOMEM;
 
-        iov.iov_base = NDISC_ROUTER_RAW(rt);
-        iov.iov_len = rt->raw_size;
+        r = icmp6_receive(fd, NDISC_ROUTER_RAW(rt), rt->raw_size, &rt->address,
+                     &rt->timestamp);
+        if (r < 0) {
+                switch (r) {
+                case -EADDRNOTAVAIL:
+                        (void) in_addr_to_string(AF_INET6, (union in_addr_union*) &rt->address, &addr);
+                        log_ndisc("Received RA from non-link-local address %s. Ignoring", addr);
+                        break;
 
-        len = recvmsg(fd, &msg, MSG_DONTWAIT);
-        if (len < 0) {
-                if (errno == EAGAIN || errno == EINTR)
-                        return 0;
+                case -EMULTIHOP:
+                        log_ndisc("Received RA with invalid hop limit. Ignoring.");
+                        break;
 
-                return log_ndisc_errno(errno, "Could not receive message from ICMPv6 socket: %m");
-        }
-
-        if ((size_t) len != rt->raw_size) {
-                log_ndisc("Packet size mismatch.");
-                return -EINVAL;
-        }
-
-        if (msg.msg_namelen == sizeof(struct sockaddr_in6) &&
-            sa.in6.sin6_family == AF_INET6)  {
-
-                if (in_addr_is_link_local(AF_INET6, (union in_addr_union*) &sa.in6.sin6_addr) <= 0) {
-                        _cleanup_free_ char *addr = NULL;
-
-                        (void) in_addr_to_string(AF_INET6, (union in_addr_union*) &sa.in6.sin6_addr, &addr);
-                        log_ndisc("Received RA from non-link-local address %s. Ignoring.", strna(addr));
-                        return 0;
+                case -EPFNOSUPPORT:
+                        log_ndisc("Received invalid source address from ICMPv6 socket.");
+                        break;
                 }
 
-                rt->address = sa.in6.sin6_addr;
-
-        } else if (msg.msg_namelen > 0) {
-                log_ndisc("Received invalid source address size from ICMPv6 socket: %zu bytes", (size_t) msg.msg_namelen);
-                return -EINVAL;
+                return 0;
         }
 
-        /* namelen == 0 only happens when running the test-suite over a socketpair */
-
-        assert(!(msg.msg_flags & MSG_CTRUNC));
-        assert(!(msg.msg_flags & MSG_TRUNC));
-
-        CMSG_FOREACH(cmsg, &msg) {
-                if (cmsg->cmsg_level == SOL_IPV6 &&
-                    cmsg->cmsg_type == IPV6_HOPLIMIT &&
-                    cmsg->cmsg_len == CMSG_LEN(sizeof(int))) {
-                        int hops = *(int*) CMSG_DATA(cmsg);
-
-                        if (hops != 255) {
-                                log_ndisc("Received RA with invalid hop limit %d. Ignoring.", hops);
-                                return 0;
-                        }
-                }
-
-                if (cmsg->cmsg_level == SOL_SOCKET &&
-                    cmsg->cmsg_type == SO_TIMESTAMP &&
-                    cmsg->cmsg_len == CMSG_LEN(sizeof(struct timeval)))
-                        triple_timestamp_from_realtime(&rt->timestamp, timeval_load((struct timeval*) CMSG_DATA(cmsg)));
-        }
-
-        if (!triple_timestamp_is_set(&rt->timestamp))
-                triple_timestamp_get(&rt->timestamp);
-
         nd->timeout_event_source = sd_event_source_unref(nd->timeout_event_source);
 
         return ndisc_handle_datagram(nd, rt);

src/libsystemd-network/sd-radv.c

@@ -93,6 +93,9 @@ static void radv_reset(sd_radv *ra) {
         ra->timeout_event_source =
                 sd_event_source_unref(ra->timeout_event_source);
 
+        ra->recv_event_source =
+                sd_event_source_unref(ra->recv_event_source);
+
         ra->ra_sent = 0;
 }
 
@@ -160,8 +163,9 @@ static int radv_send(sd_radv *ra, const struct in6_addr *dst,
                 .msg_iov = iov,
         };
 
-        if (dst)
+        if (dst && !in_addr_is_null(AF_INET6, (union in_addr_union*) dst))
                 dst_addr.sin6_addr = *dst;
+
         adv.nd_ra_type = ND_ROUTER_ADVERT;
         adv.nd_ra_curhoplimit = ra->hop_limit;
         adv.nd_ra_flags_reserved = ra->flags;
@@ -198,6 +202,63 @@ static int radv_send(sd_radv *ra, const struct in6_addr *dst,
         return 0;
 }
 
+static int radv_recv(sd_event_source *s, int fd, uint32_t revents, void *userdata) {
+        sd_radv *ra = userdata;
+        _cleanup_free_ char *addr = NULL;
+        struct in6_addr src;
+        triple_timestamp timestamp;
+        int r;
+        ssize_t buflen;
+        _cleanup_free_ char *buf = NULL;
+
+        assert(s);
+        assert(ra);
+        assert(ra->event);
+
+        buflen = next_datagram_size_fd(fd);
+
+        if ((unsigned) buflen < sizeof(struct nd_router_solicit))
+                return log_radv("Too short packet received");
+
+        buf = new0(char, buflen);
+        if (!buf)
+                return 0;
+
+        r = icmp6_receive(fd, buf, buflen, &src, &timestamp);
+        if (r < 0) {
+                switch (r) {
+                case -EADDRNOTAVAIL:
+                        (void) in_addr_to_string(AF_INET6, (union in_addr_union*) &src, &addr);
+                        log_radv("Received RS from non-link-local address %s. Ignoring", addr);
+                        break;
+
+                case -EMULTIHOP:
+                        log_radv("Received RS with invalid hop limit. Ignoring.");
+                        break;
+
+                case -EPFNOSUPPORT:
+                        log_radv("Received invalid source address from ICMPv6 socket. Ignoring.");
+                        break;
+
+                default:
+                        log_radv_warning_errno(r, "Error receiving from ICMPv6 socket: %m");
+                        break;
+                }
+
+                return 0;
+        }
+
+        (void) in_addr_to_string(AF_INET6, (union in_addr_union*) &src, &addr);
+
+        r = radv_send(ra, &src, ra->lifetime);
+        if (r < 0)
+                log_radv_warning_errno(r, "Unable to send solicited Router Advertisment to %s: %m", addr);
+        else
+                log_radv("Sent solicited Router Advertisement to %s", addr);
+
+        return 0;
+}
+
 static usec_t radv_compute_timeout(usec_t min, usec_t max) {
         assert_return(min <= max, SD_RADV_DEFAULT_MIN_TIMEOUT_USEC);
 
@@ -313,7 +374,16 @@ _public_ int sd_radv_start(sd_radv *ra) {
                 goto fail;
 
         ra->fd = r;
-        r = 0;
+
+        r = sd_event_add_io(ra->event, &ra->recv_event_source, ra->fd, EPOLLIN, radv_recv, ra);
+        if (r < 0)
+                goto fail;
+
+        r = sd_event_source_set_priority(ra->recv_event_source, ra->event_priority);
+        if (r < 0)
+                goto fail;
+
+        (void) sd_event_source_set_description(ra->recv_event_source, "radv-receive-message");
 
         ra->state = SD_RADV_STATE_ADVERTISING;
 

src/libsystemd-network/test-ndisc-rs.c

@@ -198,6 +198,16 @@ int icmp6_bind_router_advertisement(int index) {
         return -ENOSYS;
 }
 
+int icmp6_receive(int fd, void *iov_base, size_t iov_len,
+                  struct in6_addr *dst, triple_timestamp *timestamp) {
+        assert (read (fd, iov_base, iov_len) == (ssize_t)iov_len);
+
+        if (timestamp)
+                triple_timestamp_get(timestamp);
+
+        return 0;
+}
+
 static int send_ra(uint8_t flags) {
         uint8_t advertisement[] = {
                 0x86, 0x00, 0xde, 0x83, 0x40, 0xc0, 0x00, 0xb4,