Introduce FEATURE_EXEC_PREFER_APPLETS = "re-execute our own

executable if we asked to exec someting with argv[0] == known_applet"
Use it in init. Also respect PATH in init, remove explicit "/sbin" etc
from exec. Patch by Gabriel L. Somlo <somlo@cmu.edu>


git-svn-id: svn://busybox.net/trunk/busybox@17426 69ca8d6d-28ef-0310-b511-8ec308f3f277

5 files changed, 39 insertions, 12 deletions

diff --git a/Config.in b/Config.in
index acdecccab..2066e42f9 100644
--- a/Config.in
+++ b/Config.in
@@ -231,6 +231,14 @@ config SELINUX
 
           Most people will leave this set to 'N'.
 
+config FEATURE_EXEC_PREFER_APPLETS
+        bool "exec prefers applets"
+        default n
+        help
+          This is an experimental option which directs applets about to
+          call 'exec' to try and find an applicable busybox applet before
+          searching the executable path for a binary or symlink to execute.
+
 config BUSYBOX_EXEC_PATH
         string "Path to BusyBox executable"
         default "/proc/self/exe"
@@ -439,7 +447,7 @@ config INSTALL_APPLET_HARDLINKS
 config INSTALL_APPLET_DONT
        bool
        prompt "not installed"
-       depends on FEATURE_INSTALLER || FEATURE_SH_STANDALONE_SHELL
+       depends on FEATURE_INSTALLER || FEATURE_SH_STANDALONE_SHELL || FEATURE_EXEC_PREFER_APPLETS
        help
          Do not install applet links. Useful when using the -install feature
          or a standalone shell for rescue pruposes.
diff --git a/init/init.c b/init/init.c
index 6fc68afb1..7694b4448 100644
--- a/init/init.c
+++ b/init/init.c
@@ -389,6 +389,7 @@ static pid_t run(const struct init_action *a)
 #include CUSTOMIZED_BANNER
 #endif
                 "\nPlease press Enter to activate this console. ";
+        char *prog;
 
         /* Block sigchild while forking.  */
         sigemptyset(&nmask);
@@ -560,7 +561,10 @@ static pid_t run(const struct init_action *a)
 
                 /* Now run it.  The new program will take over this PID,
                  * so nothing further in init.c should be run. */
-                execv(cmdpath, cmd);
+                prog = cmdpath;
+                if (ENABLE_FEATURE_EXEC_PREFER_APPLETS && find_applet_by_name(prog))
+                        prog = CONFIG_BUSYBOX_EXEC_PATH;
+                execvp(prog, cmd);
 
                 /* We're still here?  Some error happened. */
                 message(LOG | CONSOLE, "Bummer, cannot run '%s': %m", cmdpath);
@@ -678,6 +682,7 @@ static void exec_signal(int sig ATTRIBUTE_UNUSED)
 {
         struct init_action *a, *tmp;
         sigset_t unblock_signals;
+        char *prog;
 
         for (a = init_action_list; a; a = tmp) {
                 tmp = a->next;
@@ -713,7 +718,10 @@ static void exec_signal(int sig ATTRIBUTE_UNUSED)
                         dup(0);
 
                         messageD(CONSOLE | LOG, "Trying to re-exec %s", a->command);
-                        execl(a->command, a->command, NULL);
+                        prog = a->command;
+                        if (ENABLE_FEATURE_EXEC_PREFER_APPLETS && find_applet_by_name(prog))
+                                prog = CONFIG_BUSYBOX_EXEC_PATH;
+                        execlp(prog, a->command, NULL);
 
                         message(CONSOLE | LOG, "exec of '%s' failed: %m",
                                         a->command);
@@ -852,13 +860,13 @@ static void parse_inittab(void)
                 /* No inittab file -- set up some default behavior */
 #endif
                 /* Reboot on Ctrl-Alt-Del */
-                new_init_action(CTRLALTDEL, "/sbin/reboot", "");
+                new_init_action(CTRLALTDEL, "reboot", "");
                 /* Umount all filesystems on halt/reboot */
-                new_init_action(SHUTDOWN, "/bin/umount -a -r", "");
+                new_init_action(SHUTDOWN, "umount -a -r", "");
                 /* Swapoff on halt/reboot */
-                if(ENABLE_SWAPONOFF) new_init_action(SHUTDOWN, "/sbin/swapoff -a", "");
+                if(ENABLE_SWAPONOFF) new_init_action(SHUTDOWN, "swapoff -a", "");
                 /* Prepare to restart init when a HUP is received */
-                new_init_action(RESTART, "/sbin/init", "");
+                new_init_action(RESTART, "init", "");
                 /* Askfirst shell on tty1-4 */
                 new_init_action(ASKFIRST, bb_default_login_shell, "");
                 new_init_action(ASKFIRST, bb_default_login_shell, VC_2);
@@ -1039,9 +1047,9 @@ int init_main(int argc, char **argv)
                 {
                         message(CONSOLE,"Low memory: forcing swapon.");
                         /* swapon -a requires /proc typically */
-                        new_init_action(SYSINIT, "/bin/mount -t proc proc /proc", "");
+                        new_init_action(SYSINIT, "mount -t proc proc /proc", "");
                         /* Try to turn on swap */
-                        new_init_action(SYSINIT, "/sbin/swapon -a", "");
+                        new_init_action(SYSINIT, "swapon -a", "");
                         run_actions(SYSINIT);   /* wait and removing */
                 }
         }
@@ -1068,7 +1076,10 @@ int init_main(int argc, char **argv)
 
                 putenv("SELINUX_INIT=YES");
                 if (selinux_init_load_policy(&enforce) == 0) {
-                        execv(argv[0], argv);
+                        char *prog = argv[0];
+                        if (ENABLE_FEATURE_EXEC_PREFER_APPLETS && find_applet_by_name(prog))
+                                prog = CONFIG_BUSYBOX_EXEC_PATH;
+                        execvp(prog, argv);
                 } else if (enforce > 0) {
                         /* SELinux in enforcing mode but load_policy failed */
                         /* At this point, we probably can't open /dev/console, so log() won't work */
diff --git a/libbb/xfuncs.c b/libbb/xfuncs.c
index 240ac5d3d..4252e7646 100644
--- a/libbb/xfuncs.c
+++ b/libbb/xfuncs.c
@@ -183,14 +183,17 @@ pid_t spawn(char **argv)
         /* Why static? */
         static int failed;
         pid_t pid;
-        void *app = ENABLE_FEATURE_SH_STANDALONE_SHELL ? find_applet_by_name(argv[0]) : 0;
+        char *prog;
 
         // Be nice to nommu machines.
         failed = 0;
         pid = vfork();
         if (pid < 0) return pid;
         if (!pid) {
-                execvp(app ? CONFIG_BUSYBOX_EXEC_PATH : *argv, argv);
+                prog = argv[0];
+                if (ENABLE_FEATURE_EXEC_PREFER_APPLETS && find_applet_by_name(prog))
+                        prog = CONFIG_BUSYBOX_EXEC_PATH;
+                execvp(prog, argv);
 
                 // We're sharing a stack with blocked parent, let parent know we failed
                 // and then exit to unblock parent (but don't run atexit() stuff, which
diff --git a/scripts/defconfig b/scripts/defconfig
index 2c82ed474..fc43deb2d 100644
--- a/scripts/defconfig
+++ b/scripts/defconfig
@@ -27,6 +27,7 @@ CONFIG_FEATURE_SYSLOG=y
 CONFIG_FEATURE_SUID_CONFIG=y
 CONFIG_FEATURE_SUID_CONFIG_QUIET=y
 # CONFIG_SELINUX is not set
+#CONFIG_FEATURE_EXEC_PREFER_APPLETS is not set
 CONFIG_BUSYBOX_EXEC_PATH="/proc/self/exe"
 
 #
diff --git a/shell/ash.c b/shell/ash.c
index 8ef8c465c..2db3302c7 100644
--- a/shell/ash.c
+++ b/shell/ash.c
@@ -6528,6 +6528,10 @@ setjobctl(int on)
                 int ofd;
                 ofd = fd = open(_PATH_TTY, O_RDWR);
                 if (fd < 0) {
+        /* BTW, bash will try to open(ttyname(0)) if open("/dev/tty") fails.
+         * That sometimes helps to acquire controlling tty.
+         * Obviously, a workaround for bugs when someone
+         * failed to provide a controlling tty to bash! :) */
                         fd += 3;
                         while (!isatty(fd) && --fd >= 0)
                                 ;