dhcpcd: Setup a socketpair in the launcher to write to stderr

Rather than duping stderr down to the processes.
This allows us to reopen stdout and stderr onto /dev/null right
away and means only the launcher process writes to stderr.

The downside is that any stdout from the script is now lost.
If that's needed, we could setup a stdout socketpair as well.

diff --git a/src/dhcpcd.c b/src/dhcpcd.c
index 2dc98d6c21afcf2e53d70654f9a06af0062fa555..86b994f8aa7df4ec9049899d62652a5492173e08 100644 (file)
--- a/src/dhcpcd.c
+++ b/src/dhcpcd.c
@@ -1776,6 +1776,23 @@ dhcpcd_fork_cb(void *arg)
        eloop_exit(ctx->eloop, exit_code);
 }
 
+static void
+dhcpcd_stderr_cb(void *arg)
+{
+       struct dhcpcd_ctx *ctx = arg;
+       char log[BUFSIZ];
+       ssize_t len;
+
+       len = read(ctx->stderr_fd, log, sizeof(log));
+       if (len == -1) {
+               logerr(__func__);
+               return;
+       }
+
+       log[len] = '\0';
+       fprintf(stderr, "%s", log);
+}
+
 int
 main(int argc, char **argv)
 {
@@ -1789,7 +1806,7 @@ main(int argc, char **argv)
        ssize_t len;
 #if defined(USE_SIGNALS) || !defined(THERE_IS_NO_FORK)
        pid_t pid;
-       int sigpipe[2];
+       int fork_fd[2], stderr_fd[2];
 #endif
 #ifdef USE_SIGNALS
        int sig = 0;
@@ -2223,12 +2240,16 @@ printpidfile:
 #endif
 
 #if defined(USE_SIGNALS) && !defined(THERE_IS_NO_FORK)
-       if (pipe(sigpipe) == -1) {
-               logerr("pipe");
+       if (xsocketpair(AF_UNIX, SOCK_DGRAM | SOCK_CXNB, 0, fork_fd) == -1 ||
+           xsocketpair(AF_UNIX, SOCK_DGRAM | SOCK_CXNB, 0, stderr_fd) == -1)
+       {
+               logerr("socketpair");
                goto exit_failure;
        }
 #ifdef HAVE_CAPSICUM
-       if (ps_rights_limit_fdpair(sigpipe) == -1) {
+       if (ps_rights_limit_fdpair(fork_fd) == -1 ||
+           ps_rights_limit_fdpair(stderr_fd) == 1)
+       {
                logerr("ps_rights_limit_fdpair");
                goto exit_failure;
        }
@@ -2238,8 +2259,13 @@ printpidfile:
                logerr("fork");
                goto exit_failure;
        case 0:
-               ctx.fork_fd = sigpipe[1];
-               close(sigpipe[0]);
+               ctx.fork_fd = fork_fd[1];
+               close(fork_fd[0]);
+               logseterrfd(stderr_fd[1]);
+               close(stderr_fd[0]);
+               if (freopen(_PATH_DEVNULL, "w", stdout) == NULL ||
+                   freopen(_PATH_DEVNULL, "w", stderr) == NULL)
+                       logerr("freopen");
                if (setsid() == -1) {
                        logerr("%s: setsid", __func__);
                        goto exit_failure;
@@ -2259,10 +2285,13 @@ printpidfile:
                break;
        default:
                ctx.options |= DHCPCD_FORKED; /* A lie */
-               ctx.fork_fd = sigpipe[0];
-               close(sigpipe[1]);
+               ctx.fork_fd = fork_fd[0];
+               close(fork_fd[1]);
+               ctx.stderr_fd = stderr_fd[0];
+               close(stderr_fd[1]);
                setproctitle("[launcher]");
                eloop_event_add(ctx.eloop, ctx.fork_fd, dhcpcd_fork_cb, &ctx);
+               eloop_event_add(ctx.eloop, ctx.stderr_fd, dhcpcd_stderr_cb, &ctx);
                goto run_loop;
        }
 
@@ -2281,22 +2310,6 @@ printpidfile:
                if_disable_rtadv();
 #endif
 
-       if (isatty(STDOUT_FILENO) &&
-           freopen(_PATH_DEVNULL, "r", stdout) == NULL)
-               logerr("%s: freopen stdout", __func__);
-       if (isatty(STDERR_FILENO)) {
-               int fd = dup(STDERR_FILENO);
-
-               if (fd == -1)
-                       logerr("%s: dup", __func__);
-               else if (logseterrfd(fd) == -1)
-                       logerr("%s: logseterrfd", __func__);
-               else if (freopen(_PATH_DEVNULL, "r", stderr) == NULL) {
-                       logseterrfd(-1);
-                       logerr("%s: freopen stderr", __func__);
-               }
-       }
-
 #ifdef PRIVSEP
        if (IN_PRIVSEP(&ctx) && ps_start(&ctx) == -1) {
                logerr("ps_start");

diff --git a/src/dhcpcd.h b/src/dhcpcd.h
index d9719c0a4a7c99a805d1b9c7e7eb28a2ec453893..95b7e07370bd812f9cc4611ee4d5d302899279a2 100644 (file)
--- a/src/dhcpcd.h
+++ b/src/dhcpcd.h
@@ -118,6 +118,7 @@ struct dhcpcd_ctx {
        char pidfile[sizeof(PIDFILE) + IF_NAMESIZE + 1];
        char vendor[256];
        int fork_fd;    /* FD for the fork init signal pipe */
+       int stderr_fd;  /* FD for logging to stderr */
        const char *cffile;
        unsigned long long options;
        char *logfile;