init: fix "while true; do reboot; done" bug. +15 bytes. Closes bug 781

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

1 files changed, 59 insertions, 42 deletions

diff --git a/init/init.c b/init/init.c
index 3748a1507..89bbafd13 100644
--- a/init/init.c
+++ b/init/init.c
@@ -260,6 +260,20 @@ static int open_stdio_to_tty(const char* tty_name)
         return 1; /* success */
 }
 
+static void reset_sighandlers_and_unblock_sigs(void)
+{
+        bb_signals(0
+                + (1 << SIGUSR1)
+                + (1 << SIGUSR2)
+                + (1 << SIGTERM)
+                + (1 << SIGQUIT)
+                + (1 << SIGINT)
+                + (1 << SIGHUP)
+                + (1 << SIGTSTP)
+                , SIG_DFL);
+        sigprocmask_allsigs(SIG_UNBLOCK);
+}
+
 /* Wrapper around exec:
  * Takes string (max COMMAND_SIZE chars).
  * If chars like '>' detected, execs '[-]/bin/sh -c "exec ......."'.
@@ -329,16 +343,7 @@ static pid_t run(const struct init_action *a)
         /* Child */
 
         /* Reset signal handlers that were set by the parent process */
-        bb_signals(0
-                + (1 << SIGUSR1)
-                + (1 << SIGUSR2)
-                + (1 << SIGTERM)
-                + (1 << SIGQUIT)
-                + (1 << SIGINT)
-                + (1 << SIGHUP)
-                + (1 << SIGTSTP)
-                , SIG_DFL);
-        sigprocmask_allsigs(SIG_UNBLOCK);
+        reset_sighandlers_and_unblock_sigs();
 
         /* Create a new session and make ourself the process group leader */
         setsid();
@@ -651,12 +656,21 @@ static void run_shutdown_and_kill_processes(void)
  * and only one will be remembered and acted upon.
  */
 
+/* The SIGUSR[12]/SIGTERM handler */
 static void halt_reboot_pwoff(int sig) NORETURN;
 static void halt_reboot_pwoff(int sig)
 {
         const char *m;
         unsigned rb;
 
+        /* We may call run() and it unmasks signals,
+         * including the one masked inside this signal handler.
+         * Testcase which would start multiple reboot scripts:
+         *  while true; do reboot; done
+         * Preventing it:
+         */
+        reset_sighandlers_and_unblock_sigs();
+
         run_shutdown_and_kill_processes();
 
         m = "halt";
@@ -673,38 +687,6 @@ static void halt_reboot_pwoff(int sig)
         /* not reached */
 }
 
-/* The SIGSTOP/SIGTSTP handler
- * NB: inside it, all signals except SIGCONT are masked
- * via appropriate setup in sigaction().
- */
-static void stop_handler(int sig UNUSED_PARAM)
-{
-        smallint saved_bb_got_signal;
-        int saved_errno;
-
-        saved_bb_got_signal = bb_got_signal;
-        saved_errno = errno;
-        signal(SIGCONT, record_signo);
-
-        while (1) {
-                pid_t wpid;
-
-                if (bb_got_signal == SIGCONT)
-                        break;
-                /* NB: this can accidentally wait() for a process
-                 * which we waitfor() elsewhere! waitfor() must have
-                 * code which is resilient against this.
-                 */
-                wpid = wait_any_nohang(NULL);
-                mark_terminated(wpid);
-                sleep(1);
-        }
-
-        signal(SIGCONT, SIG_DFL);
-        errno = saved_errno;
-        bb_got_signal = saved_bb_got_signal;
-}
-
 /* Handler for QUIT - exec "restart" action,
  * else (no such action defined) do nothing */
 static void restart_handler(int sig UNUSED_PARAM)
@@ -719,6 +701,9 @@ static void restart_handler(int sig UNUSED_PARAM)
                  * Thus don't need to worry about preserving errno
                  * and such.
                  */
+
+                reset_sighandlers_and_unblock_sigs();
+
                 run_shutdown_and_kill_processes();
 
                 /* Allow Ctrl-Alt-Del to reboot the system.
@@ -744,6 +729,38 @@ static void restart_handler(int sig UNUSED_PARAM)
         }
 }
 
+/* The SIGSTOP/SIGTSTP handler
+ * NB: inside it, all signals except SIGCONT are masked
+ * via appropriate setup in sigaction().
+ */
+static void stop_handler(int sig UNUSED_PARAM)
+{
+        smallint saved_bb_got_signal;
+        int saved_errno;
+
+        saved_bb_got_signal = bb_got_signal;
+        saved_errno = errno;
+        signal(SIGCONT, record_signo);
+
+        while (1) {
+                pid_t wpid;
+
+                if (bb_got_signal == SIGCONT)
+                        break;
+                /* NB: this can accidentally wait() for a process
+                 * which we waitfor() elsewhere! waitfor() must have
+                 * code which is resilient against this.
+                 */
+                wpid = wait_any_nohang(NULL);
+                mark_terminated(wpid);
+                sleep(1);
+        }
+
+        signal(SIGCONT, SIG_DFL);
+        errno = saved_errno;
+        bb_got_signal = saved_bb_got_signal;
+}
+
 #if ENABLE_FEATURE_USE_INITTAB
 static void reload_inittab(void)
 {