sockets: check that the named file descriptor is a socket

The SocketAddress struct has an "fd" type, which references the name of a
file descriptor passed over the monitor using the "getfd" command. We
currently blindly assume the FD is a socket, which can lead to hard to
diagnose errors later. This adds an explicit check that the FD is actually
a socket to improve the error diagnosis.

Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>

tests/test-util-sockets.c

@@ -23,6 +23,7 @@
 #include "qemu/sockets.h"
 #include "qapi/error.h"
 #include "socket-helpers.h"
+#include "monitor/monitor.h"
 
 static void test_fd_is_socket_bad(void)
 {
@@ -49,6 +50,90 @@ static void test_fd_is_socket_good(void)
     close(fd);
 }
 
+static int mon_fd = -1;
+static const char *mon_fdname;
+
+int monitor_get_fd(Monitor *mon, const char *fdname, Error **errp)
+{
+    g_assert(cur_mon);
+    g_assert(mon == cur_mon);
+    if (mon_fd == -1 || !g_str_equal(mon_fdname, fdname)) {
+        error_setg(errp, "No fd named %s", fdname);
+        return -1;
+    }
+    return dup(mon_fd);
+}
+
+/* Syms in libqemustub.a are discarded at .o file granularity.
+ * To replace monitor_get_fd() we must ensure everything in
+ * stubs/monitor.c is defined, to make sure monitor.o is discarded
+ * otherwise we get duplicate syms at link time.
+ */
+Monitor *cur_mon;
+void monitor_init(Chardev *chr, int flags) {}
+
+
+static void test_socket_fd_pass_good(void)
+{
+    SocketAddress addr;
+    int fd;
+
+    cur_mon = g_malloc(1); /* Fake a monitor */
+    mon_fdname = "myfd";
+    mon_fd = qemu_socket(AF_INET, SOCK_STREAM, 0);
+    g_assert_cmpint(mon_fd, >, STDERR_FILENO);
+
+    addr.type = SOCKET_ADDRESS_TYPE_FD;
+    addr.u.fd.str = g_strdup(mon_fdname);
+
+    fd = socket_connect(&addr, &error_abort);
+    g_assert_cmpint(fd, !=, -1);
+    g_assert_cmpint(fd, !=, mon_fd);
+    close(fd);
+
+    fd = socket_listen(&addr, &error_abort);
+    g_assert_cmpint(fd, !=, -1);
+    g_assert_cmpint(fd, !=, mon_fd);
+    close(fd);
+
+    g_free(addr.u.fd.str);
+    mon_fdname = NULL;
+    close(mon_fd);
+    mon_fd = -1;
+    g_free(cur_mon);
+    cur_mon = NULL;
+}
+
+static void test_socket_fd_pass_bad(void)
+{
+    SocketAddress addr;
+    Error *err = NULL;
+    int fd;
+
+    cur_mon = g_malloc(1); /* Fake a monitor */
+    mon_fdname = "myfd";
+    mon_fd = dup(STDOUT_FILENO);
+    g_assert_cmpint(mon_fd, >, STDERR_FILENO);
+
+    addr.type = SOCKET_ADDRESS_TYPE_FD;
+    addr.u.fd.str = g_strdup(mon_fdname);
+
+    fd = socket_connect(&addr, &err);
+    g_assert_cmpint(fd, ==, -1);
+    error_free_or_abort(&err);
+
+    fd = socket_listen(&addr, &err);
+    g_assert_cmpint(fd, ==, -1);
+    error_free_or_abort(&err);
+
+    g_free(addr.u.fd.str);
+    mon_fdname = NULL;
+    close(mon_fd);
+    mon_fd = -1;
+    g_free(cur_mon);
+    cur_mon = NULL;
+}
+
 int main(int argc, char **argv)
 {
     bool has_ipv4, has_ipv6;
@@ -71,6 +156,10 @@ int main(int argc, char **argv)
                         test_fd_is_socket_bad);
         g_test_add_func("/util/socket/is-socket/good",
                         test_fd_is_socket_good);
+        g_test_add_func("/socket/fd-pass/good",
+                        test_socket_fd_pass_good);
+        g_test_add_func("/socket/fd-pass/bad",
+                        test_socket_fd_pass_bad);
     }
 
     return g_test_run();

util/qemu-sockets.c

@@ -1042,6 +1042,20 @@ SocketAddress *socket_parse(const char *str, Error **errp)
     return NULL;
 }
 
+static int socket_get_fd(const char *fdstr, Error **errp)
+{
+    int fd = monitor_get_fd(cur_mon, fdstr, errp);
+    if (fd < 0) {
+        return -1;
+    }
+    if (!fd_is_socket(fd)) {
+        error_setg(errp, "File descriptor '%s' is not a socket", fdstr);
+        close(fd);
+        return -1;
+    }
+    return fd;
+}
+
 int socket_connect(SocketAddress *addr, Error **errp)
 {
     int fd;
@@ -1056,7 +1070,7 @@ int socket_connect(SocketAddress *addr, Error **errp)
         break;
 
     case SOCKET_ADDRESS_TYPE_FD:
-        fd = monitor_get_fd(cur_mon, addr->u.fd.str, errp);
+        fd = socket_get_fd(addr->u.fd.str, errp);
         break;
 
     case SOCKET_ADDRESS_TYPE_VSOCK:
@@ -1083,7 +1097,7 @@ int socket_listen(SocketAddress *addr, Error **errp)
         break;
 
     case SOCKET_ADDRESS_TYPE_FD:
-        fd = monitor_get_fd(cur_mon, addr->u.fd.str, errp);
+        fd = socket_get_fd(addr->u.fd.str, errp);
         break;
 
     case SOCKET_ADDRESS_TYPE_VSOCK: