libbb: spawn_and_wait() fflushes before forking NOEXEC; child reinits logmode

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

3 files changed, 35 insertions, 22 deletions

diff --git a/docs/nofork_noexec.txt b/docs/nofork_noexec.txt
index 2fb184a03..a24dd9c27 100644
--- a/docs/nofork_noexec.txt
+++ b/docs/nofork_noexec.txt
@@ -99,6 +99,13 @@ applet_name. Thus, for example, caller does not need to worry about
 option_mask32 getting trashed.
 
 
+        Calling NOEXEC applets
+
+It's the same trusty spawn_and_wait(argv). If FEATURE_PREFER_APPLETS=y,
+it does NOEXEC trick. It resets xfunc_error_retval = 1 and
+logmode = LOGMODE_STDIO in the child.
+
+
         Relevant CONFIG options
 
 FEATURE_PREFER_APPLETS
diff --git a/include/libbb.h b/include/libbb.h
index 8c652e2d7..07fe20dac 100644
--- a/include/libbb.h
+++ b/include/libbb.h
@@ -1093,10 +1093,19 @@ pid_t wait_any_nohang(int *wstat) FAST_FUNC;
  */
 int wait4pid(pid_t pid) FAST_FUNC;
 int wait_for_exitstatus(pid_t pid) FAST_FUNC;
+/************************************************************************/
+/* spawn_and_wait/run_nofork_applet/run_applet_no_and_exit need to work */
+/* carefully together to reinit some global state while not disturbing  */
+/* other. Be careful if you change them. Consult docs/nofork_noexec.txt */
+/************************************************************************/
 /* Same as wait4pid(spawn(argv)), but with NOFORK/NOEXEC if configured: */
 int spawn_and_wait(char **argv) FAST_FUNC;
 /* Does NOT check that applet is NOFORK, just blindly runs it */
 int run_nofork_applet(int applet_no, char **argv) FAST_FUNC;
+#ifndef BUILD_INDIVIDUAL
+extern int find_applet_by_name(const char *name) FAST_FUNC;
+extern void run_applet_no_and_exit(int a, char **argv) NORETURN FAST_FUNC;
+#endif
 
 /* Helpers for daemonization.
  *
@@ -1303,11 +1312,6 @@ const struct hwtype *get_hwtype(const char *name) FAST_FUNC;
 const struct hwtype *get_hwntype(int type) FAST_FUNC;
 
 
-#ifndef BUILD_INDIVIDUAL
-extern int find_applet_by_name(const char *name) FAST_FUNC;
-extern void run_applet_no_and_exit(int a, char **argv) NORETURN FAST_FUNC;
-#endif
-
 #ifdef HAVE_MNTENT_H
 extern int match_fstype(const struct mntent *mt, const char *fstypes) FAST_FUNC;
 extern struct mntent *find_mount_point(const char *name, int subdir_too) FAST_FUNC;
diff --git a/libbb/vfork_daemon_rexec.c b/libbb/vfork_daemon_rexec.c
index c192829b5..2e7dc2d9b 100644
--- a/libbb/vfork_daemon_rexec.c
+++ b/libbb/vfork_daemon_rexec.c
@@ -183,26 +183,28 @@ int FAST_FUNC spawn_and_wait(char **argv)
 #if ENABLE_FEATURE_PREFER_APPLETS
         int a = find_applet_by_name(argv[0]);
 
-        if (a >= 0 && (APPLET_IS_NOFORK(a)
-# if BB_MMU
-                        || APPLET_IS_NOEXEC(a) /* NOEXEC trick needs fork() */
-# endif
-        )) {
-# if BB_MMU
+        if (a >= 0) {
                 if (APPLET_IS_NOFORK(a))
-# endif
-                {
                         return run_nofork_applet(a, argv);
+# if BB_MMU /* NOEXEC needs fork(), thus this is done only on MMU machines: */
+                if (APPLET_IS_NOEXEC(a)) {
+                        fflush_all();
+                        rc = fork();
+                        if (rc) /* parent or error */
+                                return wait4pid(rc);
+
+                        /* child */
+                        /* reset some state and run without execing */
+
+                        /* msg_eol = "\n"; - no caller needs this reinited yet */
+                        logmode = LOGMODE_STDIO;
+                        /* die_func = NULL; - needed if the caller is a shell,
+                         * init, or a NOFORK applet. But none of those call us
+                         * as of yet (and that should probably always stay true).
+                         */
+                        /* xfunc_error_retval and applet_name are init by: */
+                        run_applet_no_and_exit(a, argv);
                 }
-# if BB_MMU
-                /* MMU only */
-                /* a->noexec is true */
-                rc = fork();
-                if (rc) /* parent or error */
-                        return wait4pid(rc);
-                /* child */
-                xfunc_error_retval = EXIT_FAILURE;
-                run_applet_no_and_exit(a, argv);
 # endif
         }
 #endif /* FEATURE_PREFER_APPLETS */