From: Roy Marples <roy@marples.name>
Date: Sat, 5 Sep 2020 15:16:22 +0000 (+0100)
Subject: dhcpcd: Setup a socketpair in the launcher to write to stderr
X-Git-Tag: v9.2.0~11
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=bb70c7ebdf80a3ee7d5146a877061503bf58c6d4;p=thirdparty%2Fdhcpcd.git

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 2dc98d6c..86b994f8 100644
--- 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 d9719c0a..95b7e073 100644
--- 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;