networkd: FIONREAD is not reliable on some sockets

Fixes: #2457

4 files changed, 24 insertions, 34 deletions

diff --git a/src/libsystemd-network/sd-dhcp-client.c b/src/libsystemd-network/sd-dhcp-client.c
index 5fd59f7dd3..62099dd3f4 100644
--- a/src/libsystemd-network/sd-dhcp-client.c
+++ b/src/libsystemd-network/sd-dhcp-client.c
@@ -1525,20 +1525,17 @@ static int client_receive_message_udp(sd_event_source *s, int fd,
                                       uint32_t revents, void *userdata) {
         sd_dhcp_client *client = userdata;
         _cleanup_free_ DHCPMessage *message = NULL;
-        int buflen = 0, len, r;
         const struct ether_addr zero_mac = { { 0, 0, 0, 0, 0, 0 } };
         const struct ether_addr *expected_chaddr = NULL;
         uint8_t expected_hlen = 0;
+        ssize_t len, buflen;
 
         assert(s);
         assert(client);
 
-        r = ioctl(fd, FIONREAD, &buflen);
-        if (r < 0)
-                return -errno;
-        else if (buflen < 0)
-                /* this can't be right */
-                return -EIO;
+        buflen = next_datagram_size_fd(fd);
+        if (buflen < 0)
+                return buflen;
 
         message = malloc0(buflen);
         if (!message)
@@ -1616,17 +1613,15 @@ static int client_receive_message_raw(sd_event_source *s, int fd,
         };
         struct cmsghdr *cmsg;
         bool checksum = true;
-        int buflen = 0, len, r;
+        ssize_t buflen, len;
+        int r;
 
         assert(s);
         assert(client);
 
-        r = ioctl(fd, FIONREAD, &buflen);
-        if (r < 0)
-                return -errno;
-        else if (buflen < 0)
-                /* this can't be right */
-                return -EIO;
+        buflen = next_datagram_size_fd(fd);
+        if (buflen < 0)
+                return buflen;
 
         packet = malloc0(buflen);
         if (!packet)
diff --git a/src/libsystemd-network/sd-dhcp-server.c b/src/libsystemd-network/sd-dhcp-server.c
index ad3a37b722..54ff1a3f28 100644
--- a/src/libsystemd-network/sd-dhcp-server.c
+++ b/src/libsystemd-network/sd-dhcp-server.c
@@ -955,14 +955,13 @@ static int server_receive_message(sd_event_source *s, int fd,
                 .msg_controllen = sizeof(cmsgbuf),
         };
         struct cmsghdr *cmsg;
-        int buflen = 0, len;
+        ssize_t buflen, len;
 
         assert(server);
 
-        if (ioctl(fd, FIONREAD, &buflen) < 0)
-                return -errno;
-        else if (buflen < 0)
-                return -EIO;
+        buflen = next_datagram_size_fd(fd);
+        if (buflen < 0)
+                return buflen;
 
         message = malloc(buflen);
         if (!message)
diff --git a/src/libsystemd-network/sd-dhcp6-client.c b/src/libsystemd-network/sd-dhcp6-client.c
index 5b6b9cbcac..7d56d4cc60 100644
--- a/src/libsystemd-network/sd-dhcp6-client.c
+++ b/src/libsystemd-network/sd-dhcp6-client.c
@@ -33,6 +33,7 @@
 #include "in-addr-util.h"
 #include "network-internal.h"
 #include "random-util.h"
+#include "socket-util.h"
 #include "string-table.h"
 #include "util.h"
 
@@ -891,18 +892,16 @@ static int client_receive_message(sd_event_source *s, int fd, uint32_t revents,
         sd_dhcp6_client *client = userdata;
         DHCP6_CLIENT_DONT_DESTROY(client);
         _cleanup_free_ DHCP6Message *message = NULL;
-        int r, buflen, len;
+        ssize_t buflen, len;
+        int r = 0;
 
         assert(s);
         assert(client);
         assert(client->event);
 
-        r = ioctl(fd, FIONREAD, &buflen);
-        if (r < 0)
-                return -errno;
-        else if (buflen < 0)
-                /* This really should not happen */
-                return -EIO;
+        buflen = next_datagram_size_fd(fd);
+        if (buflen < 0)
+                return buflen;
 
         message = malloc(buflen);
         if (!message)
diff --git a/src/libsystemd-network/sd-ndisc.c b/src/libsystemd-network/sd-ndisc.c
index 519d2aa36b..bae6a49fe6 100644
--- a/src/libsystemd-network/sd-ndisc.c
+++ b/src/libsystemd-network/sd-ndisc.c
@@ -491,19 +491,16 @@ static int ndisc_router_advertisment_recv(sd_event_source *s, int fd, uint32_t r
         struct cmsghdr *cmsg;
         struct in6_addr *gw;
         unsigned lifetime;
-        ssize_t len;
-        int r, pref, stateful, buflen = 0;
+        ssize_t len, buflen;
+        int r, pref, stateful;
 
         assert(s);
         assert(nd);
         assert(nd->event);
 
-        r = ioctl(fd, FIONREAD, &buflen);
-        if (r < 0)
-                return -errno;
-        else if (buflen < 0)
-                /* This really should not happen */
-                return -EIO;
+        buflen = next_datagram_size_fd(fd);
+        if (buflen < 0)
+                return buflen;
 
         iov.iov_len = buflen;