ftpd: do not use nasty tricks for re-execing if we are on MMU machine.

On NOMMU, code is alomost the same, on MMU:

function                                             old     new   delta
handle_dir_common                                    223     390    +167
ftpd_main                                           2306    2231     -75
popen_ls                                             203       -    -203
------------------------------------------------------------------------------
(add/remove: 0/1 grow/shrink: 1/1 up/down: 167/-278)         Total: -111 bytes

1 files changed, 57 insertions, 22 deletions

diff --git a/networking/ftpd.c b/networking/ftpd.c
index b295ddf4f..0a4b185a1 100644
--- a/networking/ftpd.c
+++ b/networking/ftpd.c
@@ -87,7 +87,9 @@ enum {
 
 struct globals {
         int pasv_listen_fd;
-        int proc_self_fd;
+#if !BB_MMU
+        int root_fd;
+#endif
         int local_file_fd;
         unsigned end_time;
         unsigned timeout;
@@ -615,7 +617,13 @@ static int
 popen_ls(const char *opt)
 {
         char *cwd;
-        const char *argv[5] = { "ftpd", opt, NULL, G.ftp_arg, NULL };
+        const char *argv[] = {
+                        "ftpd",
+                        opt,
+                        BB_MMU ? "--" : NULL,
+                        G.ftp_arg,
+                        NULL
+        };
         struct fd_pair outfd;
         pid_t pid;
 
@@ -623,25 +631,40 @@ popen_ls(const char *opt)
         xpiped_pair(outfd);
 
         /*fflush(NULL); - so far we dont use stdio on output */
-        pid = vfork();
-        switch (pid) {
-        case -1:  /* failure */
-                bb_perror_msg_and_die("vfork");
-        case 0:  /* child */
-                /* NB: close _first_, then move fds! */
+        pid = BB_MMU ? fork() : vfork();
+        if (pid < 0)
+                bb_perror_msg_and_die(BB_MMU ? "fork" : "vfork");
+
+        if (pid == 0) {
+                /* child */
+#if !BB_MMU
+                if (fchdir(G.root_fd) != 0)
+                        _exit(127);
+                close(G.root_fd);
+#endif
+                /* NB: close _first_, then move fd! */
                 close(outfd.rd);
                 xmove_fd(outfd.wr, STDOUT_FILENO);
+                /* Opening /dev/null in chroot is hard.
+                 * Just making sure STDIN_FILENO is opened
+                 * to something harmless. Paranoia,
+                 * ls won't read it anyway */
                 close(STDIN_FILENO);
-                /* xopen("/dev/null", O_RDONLY); - chroot may lack it! */
-                if (fchdir(G.proc_self_fd) == 0) {
-                        close(G.proc_self_fd);
-                        argv[2] = cwd;
-                        /* ftpd ls helper chdirs to argv[2],
-                         * preventing peer from seeing /proc/self
-                         */
-                        execv("exe", (char**) argv);
-                }
+                dup(STDOUT_FILENO); /* copy will become STDIN_FILENO */
+#if !BB_MMU
+                /* ftpd ls helper chdirs to argv[2],
+                 * preventing peer from seeing real root we are in now
+                 */
+                argv[2] = cwd;
+                /* + 1: we must use relative path here if in chroot.
+                 * For example, execv("/proc/self/exe") will fail, since
+                 * it looks for "/proc/self/exe" _relative to chroot!_ */
+                execv(CONFIG_BUSYBOX_EXEC_PATH + 1, (char**) argv);
                 _exit(127);
+#else
+                memset(&G, 0, sizeof(G));
+                exit(ls_main(ARRAY_SIZE(argv) - 1, (char**) argv));
+#endif
         }
 
         /* parent */
@@ -1006,15 +1029,21 @@ enum {
         const_TYPE = mk_const4('T', 'Y', 'P', 'E'),
         const_USER = mk_const4('U', 'S', 'E', 'R'),
 
+#if !BB_MMU
         OPT_l = (1 << 0),
         OPT_1 = (1 << 1),
-        OPT_v = (1 << 2),
-        OPT_S = (1 << 3),
-        OPT_w = (1 << 4),
+#endif
+        OPT_v = (1 << ((!BB_MMU) * 2 + 0)),
+        OPT_S = (1 << ((!BB_MMU) * 2 + 1)),
+        OPT_w = (1 << ((!BB_MMU) * 2 + 2)) * ENABLE_FEATURE_FTP_WRITE,
 };
 
 int ftpd_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
+#if !BB_MMU
 int ftpd_main(int argc, char **argv)
+#else
+int ftpd_main(int argc UNUSED_PARAM, char **argv)
+#endif
 {
         unsigned abs_timeout;
         smallint opts;
@@ -1024,16 +1053,20 @@ int ftpd_main(int argc, char **argv)
         abs_timeout = 1 * 60 * 60;
         G.timeout = 2 * 60;
         opt_complementary = "t+:T+:vv";
+#if BB_MMU
+        opts = getopt32(argv,   "vS" USE_FEATURE_FTP_WRITE("w") "t:T:", &G.timeout, &abs_timeout, &G.verbose);
+#else
         opts = getopt32(argv, "l1vS" USE_FEATURE_FTP_WRITE("w") "t:T:", &G.timeout, &abs_timeout, &G.verbose);
         if (opts & (OPT_l|OPT_1)) {
                 /* Our secret backdoor to ls */
-                memset(&G, 0, sizeof(G));
 /* TODO: pass -n too? */
 /* --group-directories-first would be nice, but ls don't do that yet */
                 xchdir(argv[2]);
                 argv[2] = (char*)"--";
+                memset(&G, 0, sizeof(G));
                 return ls_main(argc, argv);
         }
+#endif
         if (abs_timeout | G.timeout) {
                 if (abs_timeout == 0)
                         abs_timeout = INT_MAX;
@@ -1065,7 +1098,9 @@ int ftpd_main(int argc, char **argv)
         if (logmode)
                 applet_name = xasprintf("%s[%u]", applet_name, (int)getpid());
 
-        G.proc_self_fd = xopen("/proc/self", O_RDONLY | O_DIRECTORY);
+#if !BB_MMU
+        G.root_fd = xopen("/", O_RDONLY | O_DIRECTORY);
+#endif
 
         if (argv[optind]) {
                 xchdir(argv[optind]);