Merge branch 'refs/heads/t/daemonize-fix'

Two bug fixes for race conditions during server startup, and an
improved log message. Cooking for two months.

* refs/heads/t/daemonize-fix:
  server: Fix race condition in afs startup.
  daemon: Fix race condition in daemonize().
  daemon: Improve "daemonizing" log message.

diff --git a/NEWS.md b/NEWS.md
index b0862d5f392ee33504255eab1d0d43e3ee157067..38d1d5b0664e26da404bbae9059e3142949fe5fe 100644 (file)
--- a/NEWS.md
+++ b/NEWS.md
@@ -8,6 +8,7 @@ NEWS
 - One of the two source browsers has been removed from the web pages.
   The doxygen API reference still contains an HTML version of each
   source file.
+- Two race conditions in para_server have been fixed.
 
 Download: [tarball](./releases/paraslash-git.tar.bz2)
 

diff --git a/afs.c b/afs.c
index 0accc45108f7c6ba0c2a3a89595d957d8a566920..071f657ce69c79812d29a982f69cc5c0bbf8f8b7 100644 (file)
--- a/afs.c
+++ b/afs.c
@@ -1024,6 +1024,13 @@ __noreturn void afs_init(uint32_t cookie, int socket_fd)
        register_command_task(cookie, &s);
        s.default_timeout.tv_sec = 0;
        s.default_timeout.tv_usec = 999 * 1000;
+       ret = write(socket_fd, "\0", 1);
+       if (ret != 1) {
+               if (ret == 0)
+                       errno = EINVAL;
+               ret = -ERRNO_TO_PARA_ERROR(errno);
+               goto out_close;
+       }
        ret = schedule(&s);
        sched_shutdown(&s);
 out_close:

diff --git a/daemon.c b/daemon.c
index 7c625bbea9d84c5ac9b37a22253346576cbb7183..20cdc6ae605a99f56f35bf41f0abeff7d508936d 100644 (file)
--- a/daemon.c
+++ b/daemon.c
@@ -155,10 +155,6 @@ static bool daemon_test_flag(unsigned flag)
        return me->flags & flag;
 }
 
-static void dummy_sighandler(__a_unused int s)
-{
-}
-
 /**
  * Do the usual stuff to become a daemon.
  *
@@ -166,30 +162,42 @@ static void dummy_sighandler(__a_unused int s)
  *
  * Fork, become session leader, cd to /, and dup fd 0, 1, 2 to /dev/null. If \a
  * parent_waits is false, the parent process terminates immediately.
- * Otherwise, it calls pause() to sleep until it receives \p SIGTERM or \p
- * SIGCHLD and exits successfully thereafter. This behaviour is useful if the
- * daemon process should not detach from the console until the child process
- * has completed its setup.
+ * Otherwise, a pipe is created prior to the fork() and the parent tries to
+ * read a single byte from the reading end of the pipe. The child is supposed
+ * to write to the writing end of the pipe after it completed its setup
+ * procedure successfully. This behaviour is useful to let the parent process
+ * die with an error if the child process aborts early, since in this case the
+ * read() will return non-positive.
+ *
+ * \return This function either succeeds or calls exit(3). If parent_waits is
+ * true, the return value is the file descriptor of the writing end of the
+ * pipe. Otherwise the function returns zero.
  *
  * \sa fork(2), setsid(2), dup(2), pause(2).
  */
-void daemonize(bool parent_waits)
+int daemonize(bool parent_waits)
 {
        pid_t pid;
-       int null;
+       int null, pipe_fd[2];
 
-       PARA_INFO_LOG("daemonizing\n");
+       if (parent_waits && pipe(pipe_fd) < 0)
+               goto err;
+       PARA_INFO_LOG("subsequent log messages go to %s\n", me->logfile_name?
+                me->logfile_name : "/dev/null");
        pid = fork();
        if (pid < 0)
                goto err;
-       if (pid) {
+       if (pid) { /* parent exits */
                if (parent_waits) {
-                       signal(SIGTERM, dummy_sighandler);
-                       signal(SIGCHLD, dummy_sighandler);
-                       pause();
+                       char c;
+                       close(pipe_fd[1]);
+                       exit(read(pipe_fd[0], &c, 1) <= 0?
+                               EXIT_FAILURE : EXIT_SUCCESS);
                }
-               exit(EXIT_SUCCESS); /* parent exits */
+               exit(EXIT_SUCCESS);
        }
+       if (parent_waits)
+               close(pipe_fd[0]);
        /* become session leader */
        if (setsid() < 0)
                goto err;
@@ -205,7 +213,7 @@ void daemonize(bool parent_waits)
        if (dup2(null, STDERR_FILENO) < 0)
                goto err;
        close(null);
-       return;
+       return parent_waits? pipe_fd[1] : 0;
 err:
        PARA_EMERG_LOG("fatal: %s\n", strerror(errno));
        exit(EXIT_FAILURE);

diff --git a/daemon.h b/daemon.h
index c715360583d350275641042b574708fd0cd2ec04..989678df40e6b29a44ae8fb5491db05841d25bca 100644 (file)
--- a/daemon.h
+++ b/daemon.h
@@ -1,7 +1,7 @@
 /** \file daemon.h exported symbols from daemon.c */
 
 
-void daemonize(bool parent_waits);
+int daemonize(bool parent_waits);
 void daemon_open_log_or_die(void);
 void daemon_close_log(void);
 void daemon_log_welcome(const char *whoami);

diff --git a/server.c b/server.c
index 088cc8b124448123ed6f4cb73f0226f584dffc25..ca71c4d8860e49224ffd0f2203ed76a7253a1a01 100644 (file)
--- a/server.c
+++ b/server.c
@@ -411,8 +411,9 @@ static int init_afs(int argc, char **argv)
 {
        int ret, afs_server_socket[2];
        pid_t afs_pid;
+       char c;
 
-       ret = socketpair(PF_UNIX, SOCK_DGRAM, 0, afs_server_socket);
+       ret = socketpair(PF_UNIX, SOCK_STREAM, 0, afs_server_socket);
        if (ret < 0)
                exit(EXIT_FAILURE);
        get_random_bytes_or_die((unsigned char *)&afs_socket_cookie,
@@ -422,6 +423,7 @@ static int init_afs(int argc, char **argv)
                exit(EXIT_FAILURE);
        if (afs_pid == 0) { /* child (afs) */
                int i;
+
                for (i = argc - 1; i >= 0; i--)
                        memset(argv[i], 0, strlen(argv[i]));
                sprintf(argv[0], "para_server (afs)");
@@ -430,6 +432,10 @@ static int init_afs(int argc, char **argv)
        }
        mmd->afs_pid = afs_pid;
        close(afs_server_socket[1]);
+       if (read(afs_server_socket[0], &c, 1) <= 0) {
+               PARA_EMERG_LOG("early afs exit\n");
+               exit(EXIT_FAILURE);
+       }
        ret = mark_fd_nonblocking(afs_server_socket[0]);
        if (ret < 0)
                exit(EXIT_FAILURE);
@@ -457,7 +463,7 @@ static void server_init(int argc, char **argv)
                .check_ambiguity = 0,
                .print_errors = 1
        };
-       int afs_socket;
+       int afs_socket, daemon_pipe = -1;
 
        valid_fd_012();
        init_random_seed_or_die();
@@ -477,7 +483,7 @@ static void server_init(int argc, char **argv)
        init_user_list(user_list_file);
        /* become daemon */
        if (conf.daemon_given)
-               daemonize(true /* parent waits for SIGTERM */);
+               daemon_pipe = daemonize(true /* parent waits for us */);
        PARA_NOTICE_LOG("initializing audio format handlers\n");
        afh_init();
 
@@ -503,8 +509,13 @@ static void server_init(int argc, char **argv)
        PARA_NOTICE_LOG("initializing virtual streaming system\n");
        init_vss_task(afs_socket, &sched);
        init_server_command_task(argc, argv);
-       if (conf.daemon_given)
-               kill(getppid(), SIGTERM);
+       if (daemon_pipe >= 0) {
+               if (write(daemon_pipe, "\0", 1) < 0) {
+                       PARA_EMERG_LOG("daemon_pipe: %s", strerror(errno));
+                       exit(EXIT_FAILURE);
+               }
+               close(daemon_pipe);
+       }
        PARA_NOTICE_LOG("server init complete\n");
 }