mail.c: more robust handling of SIGCHLD

init: more robust signal handling

diff --git a/init/init.c b/init/init.c
index 5b9820b4a05a2cdc5c9a1d68c9cae4d8031d6573..5c344cb63c9680254ab1b9b3cf82b8d7aa6b8a61 100644 (file)
--- a/init/init.c
+++ b/init/init.c
@@ -336,20 +336,22 @@ static pid_t run(const struct init_action *a)
 {
        pid_t pid;
 
+       /* Careful: don't be affected by a signal in vforked child */
+       sigprocmask_allsigs(SIG_BLOCK);
        if (BB_MMU && (a->action_type & ASKFIRST))
                pid = fork();
        else
                pid = vfork();
        if (pid < 0)
                message(L_LOG | L_CONSOLE, "can't fork");
-       if (pid)
+       if (pid) {
+               sigprocmask_allsigs(SIG_UNBLOCK);
                return pid; /* Parent or error */
+       }
 
        /* Child */
 
        /* Reset signal handlers that were set by the parent process */
-//TODO: block signals across fork(), prevent them to affect child before
-//signals are reset?
        bb_signals(0
                + (1 << SIGUSR1)
                + (1 << SIGUSR2)
@@ -359,6 +361,7 @@ static pid_t run(const struct init_action *a)
                + (1 << SIGHUP)
                + (1 << SIGTSTP)
                , SIG_DFL);
+       sigprocmask_allsigs(SIG_UNBLOCK);
 
        /* Create a new session and make ourself the process group leader */
        setsid();
@@ -982,40 +985,42 @@ int init_main(int argc UNUSED_PARAM, char **argv)
         * NB: if delayed signal happened, avoid blocking in wait().
         */
        while (1) {
-               pid_t wpid;
-               int got_sigs;
+               int maybe_WNOHANG;
 
-               got_sigs = check_delayed_sigs();
+               maybe_WNOHANG = check_delayed_sigs();
 
                /* (Re)run the respawn/askfirst stuff */
                run_actions(RESPAWN | ASKFIRST);
-
-               got_sigs |= check_delayed_sigs();
+               maybe_WNOHANG |= check_delayed_sigs();
 
                /* Don't consume all CPU time - sleep a bit */
                sleep(1);
+               maybe_WNOHANG |= check_delayed_sigs();
 
-               got_sigs |= check_delayed_sigs();
-
-               if (got_sigs)
-                       goto dont_block;
-               /* Wait for any child process to exit.
+               /* Wait for any child process(es) to exit.
                 * NB: "delayed" signals will also interrupt this wait(),
                 * bb_signals_recursive_norestart() set them up for that.
                 * This guarantees we won't be stuck here
                 * till next orphan dies.
                 */
-               wpid = wait(NULL);
-               while (wpid > 0) {
-                       struct init_action *a = mark_terminated(wpid);
+               if (maybe_WNOHANG)
+                       maybe_WNOHANG = WNOHANG;
+               while (1) {
+                       pid_t wpid;
+                       struct init_action *a;
+
+                       wpid = waitpid(-1, NULL, maybe_WNOHANG);
+                       if (wpid <= 0)
+                               break;
+
+                       a = mark_terminated(wpid);
                        if (a) {
                                message(L_LOG, "process '%s' (pid %d) exited. "
                                                "Scheduling for restart.",
                                                a->command, wpid);
                        }
                        /* See if anyone else is waiting to be reaped */
- dont_block:
-                       wpid = wait_any_nohang(NULL);
+                       maybe_WNOHANG = WNOHANG;
                }
        } /* while (1) */
 }

diff --git a/mailutils/mail.c b/mailutils/mail.c
index 71f46c86f42fcbcd852b287a8c0ada656cd00a87..68883ff42c030097ceed6ac96d09cb14758873dd 100644 (file)
--- a/mailutils/mail.c
+++ b/mailutils/mail.c
@@ -48,6 +48,12 @@ void FAST_FUNC launch_helper(const char **argv)
        xpipe(pipes);
        xpipe(pipes + 2);
 
+       // NB: handler must be installed before vfork
+       bb_signals(0
+               + (1 << SIGCHLD)
+               + (1 << SIGALRM)
+               , signal_handler);
+
        G.helper_pid = vfork();
        if (G.helper_pid < 0)
                bb_perror_msg_and_die("vfork");
@@ -60,15 +66,12 @@ void FAST_FUNC launch_helper(const char **argv)
 
        if (!G.helper_pid) {
                // child: try to execute connection helper
+               // NB: SIGCHLD & SIGALRM revert to SIG_DFL on exec
                BB_EXECVP(*argv, (char **)argv);
                _exit(127);
        }
 
        // parent
-       bb_signals(0
-               + (1 << SIGCHLD)
-               + (1 << SIGALRM)
-               , signal_handler);
        // check whether child is alive
        //redundant:signal_handler(SIGCHLD);
        // child seems OK -> parent goes on