tcpsvd,udpsvd: make them NOMMU-capable

inetd: make udp nowait work

function                                             old     new   delta
inetd_main                                          1797    2036    +239
tcpudpsvd_main                                      1839    1973    +134
xsetenv_plain                                          -      39     +39
xsetenv_proto                                         23      40     +17
bump_nofile                                          169     170      +1
sig_term_handler                                      72      69      -3
sig_child_handler                                    239     233      -6
connection_status                                     37      31      -6
parse_one_line                                      1102    1092     -10
------------------------------------------------------------------------------
(add/remove: 1/0 grow/shrink: 4/4 up/down: 430/-25)           Total: 405 bytes
   text    data     bss     dec     hex filename
 798437     661    7428  806526   c4e7e busybox_old
 798734     661    7428  806823   c4fa7 busybox_unstripped

1 files changed, 60 insertions, 41 deletions

diff --git a/networking/inetd.c b/networking/inetd.c
index 0620188d6..41824dbc8 100644
--- a/networking/inetd.c
+++ b/networking/inetd.c
@@ -130,8 +130,13 @@
  * tening service socket, and must accept at least one connection request
  * before exiting.  Such a server would normally accept and process incoming
  * connection requests until a timeout.
- *
- * In short: "stream" can be "wait" or "nowait"; "dgram" must be "wait".
+ */
+
+/* Despite of above doc saying that dgram services must use "wait",
+ * "udp nowait" servers are implemented in busyboxed inetd.
+ * IPv6 addresses are also implemented. However, they may look ugly -
+ * ":::service..." means "address '::' (IPv6 wildcard addr)":"service"...
+ * You have to put "tcp6"/"udp6" in protocol field to select IPv6.
  */
 
 /* Here's the scoop concerning the user[:group] feature:
@@ -832,9 +837,6 @@ static NOINLINE servtab_t *parse_one_line(void)
         if (sep->se_socktype == SOCK_DGRAM) {
                 if (sep->se_proto_no == IPPROTO_TCP)
                         goto parse_err;
-                /* "udp nowait" is a small fork bomb :) */
-                if (!sep->se_wait)
-                        goto parse_err;
         }
 
         /* check if the hostname specifier is a comma separated list
@@ -1195,7 +1197,7 @@ int inetd_main(int argc, char **argv)
 
         for (;;) {
                 int ready_fd_cnt;
-                int ctrl, accepted_fd;
+                int ctrl, accepted_fd, new_udp_fd;
                 fd_set readable;
 
                 if (maxsock < 0)
@@ -1220,12 +1222,43 @@ int inetd_main(int argc, char **argv)
                         ready_fd_cnt--;
                         ctrl = sep->se_fd;
                         accepted_fd = -1;
-                        if (!sep->se_wait && sep->se_socktype == SOCK_STREAM) {
-                                ctrl = accepted_fd = accept(sep->se_fd, NULL, NULL);
-                                if (ctrl < 0) {
-                                        if (errno != EINTR)
-                                                bb_perror_msg("accept (for %s)", sep->se_service);
-                                        continue;
+                        new_udp_fd = -1;
+                        if (!sep->se_wait) {
+                                if (sep->se_socktype == SOCK_STREAM) {
+                                        ctrl = accepted_fd = accept(sep->se_fd, NULL, NULL);
+                                        if (ctrl < 0) {
+                                                if (errno != EINTR)
+                                                        bb_perror_msg("accept (for %s)", sep->se_service);
+                                                continue;
+                                        }
+                                }
+                                /* "nowait" udp */
+                                if (sep->se_socktype == SOCK_DGRAM
+                                 && sep->se_family != AF_UNIX
+                                ) {
+/* How udp "nowait" works:
+ * child peeks at (received and buffered by kernel) UDP packet,
+ * performs connect() on the socket so that it is linked only
+ * to this peer. But this also affects parent, because descriptors
+ * are shared after fork() a-la dup(). When parent performs
+ * select(), it will see this descriptor connected to the peer (!)
+ * and still readable, will act on it and mess things up
+ * (can create many copies of same child, etc).
+ * Parent must create and use new socket instead. */
+                                        new_udp_fd = socket(sep->se_family, SOCK_DGRAM, 0);
+                                        if (new_udp_fd < 0) { /* error: eat packet, forget about it */
+ udp_err:
+                                                recv(sep->se_fd, line, LINE_SIZE, MSG_DONTWAIT);
+                                                continue;
+                                        }
+                                        setsockopt_reuseaddr(new_udp_fd);
+                                        /* TODO: better do bind after vfork in parent,
+                                         * so that we don't have two wildcard bound sockets
+                                         * even for a brief moment? */
+                                        if (bind(new_udp_fd, &sep->se_lsa->u.sa, sep->se_lsa->len) < 0) {
+                                                close(new_udp_fd);
+                                                goto udp_err;
+                                        }
                                 }
                         }
 
@@ -1283,10 +1316,15 @@ int inetd_main(int argc, char **argv)
 
                         if (pid > 0) { /* parent */
                                 if (sep->se_wait) {
+                                        /* tcp wait: we passed listening socket to child,
+                                         * will wait for child to terminate */
                                         sep->se_wait = pid;
                                         remove_fd_from_set(sep->se_fd);
-                                        /* we passed listening socket to child,
-                                         * will wait for child to terminate */
+                                }
+                                if (new_udp_fd >= 0) {
+                                        /* udp nowait: child connected the socket,
+                                         * we created and will use new, unconnected one */
+                                        xmove_fd(new_udp_fd, sep->se_fd);
                                 }
                                 restore_sigmask(&omask);
                                 maybe_close(accepted_fd);
@@ -1313,39 +1351,20 @@ int inetd_main(int argc, char **argv)
 #endif
                         /* child */
                         setsid();
-#if 0
-/* This does not work.
- * Actually, it _almost_ works. The idea behind it is: child
- * can peek at (already received and buffered by kernel) UDP packet,
- * and perform connect() on the socket so that it is linked only
- * to this peer. But this also affects parent, because descriptors
- * are shared after fork() a-la dup(). When parent returns to
- * select(), it will see this descriptor attached to the peer (!)
- * and likely still readable, will act on it and mess things up
- * (can create many copies of same child, etc).
- * If child will create new socket instead, then bind() and
- * connect() it to peer's address, descriptor aliasing problem
- * is solved, but first packet cannot be "transferred" to the new
- * socket. It is not a problem if child can account for this,
- * but our child will exec - and exec'ed program does not know
- * about this "lost packet" problem! Pity... */
-                        /* "nowait" udp[6]. Hmmm... */
-                        if (!sep->se_wait
-                         && sep->se_socktype == SOCK_DGRAM
-                         && sep->se_family != AF_UNIX
-                        ) {
+                        /* "nowait" udp */
+                        if (new_udp_fd >= 0) {
                                 len_and_sockaddr *lsa = xzalloc_lsa(sep->se_family);
                                 /* peek at the packet and remember peer addr */
                                 int r = recvfrom(ctrl, NULL, 0, MSG_PEEK|MSG_DONTWAIT,
                                         &lsa->u.sa, &lsa->len);
-                                if (r >= 0)
-                                        /* make this socket "connected" to peer addr:
-                                         * only packets from this peer will be recv'ed,
-                                         * and bare write()/send() will work on it */
-                                        connect(ctrl, &lsa->u.sa, lsa->len);
+                                if (r < 0)
+                                        goto do_exit1;
+                                /* make this socket "connected" to peer addr:
+                                 * only packets from this peer will be recv'ed,
+                                 * and bare write()/send() will work on it */
+                                connect(ctrl, &lsa->u.sa, lsa->len);
                                 free(lsa);
                         }
-#endif
                         /* prepare env and exec program */
                         pwd = getpwnam(sep->se_user);
                         if (pwd == NULL) {