dhcpcd: Only manipulate stdin, stdout and stderr when valid

UNIX application expect these to exist even if pointed at /dev/null.
We cannot change which fd they use, it's always 0, 1 and 2.
But if these fd's are not open when dhcpcd is called, they could
be assigned to dhcpcd internals.

In this instance we should not use the streams in anyway or form.

1 files changed, 42 insertions, 19 deletions

diff --git a/src/dhcpcd.c b/src/dhcpcd.c
index f80d293a..1c863b5e 100644
--- a/src/dhcpcd.c
+++ b/src/dhcpcd.c
@@ -360,7 +360,7 @@ dhcpcd_daemonise(struct dhcpcd_ctx *ctx)
 		return;
 
 	/* Don't use loginfo because this makes no sense in a log. */
-	if (!(logopts & LOGERR_QUIET))
+	if (!(logopts & LOGERR_QUIET) && ctx->stderr_valid)
 		(void)fprintf(stderr,
 		    "forked to background, child pid %d\n", getpid());
 	i = EXIT_SUCCESS;
@@ -1893,9 +1893,16 @@ main(int argc, char **argv)
 	ctx.ps_inet_fd = ctx.ps_control_fd = -1;
 	TAILQ_INIT(&ctx.ps_processes);
 #endif
-	rt_init(&ctx);
 
-	logopts = LOGERR_ERR|LOGERR_LOG|LOGERR_LOG_DATE|LOGERR_LOG_PID;
+	/* Check our streams for validity */
+	ctx.stdin_valid =  fcntl(STDIN_FILENO,  F_GETFD) != -1;
+	ctx.stdout_valid = fcntl(STDOUT_FILENO, F_GETFD) != -1;
+	ctx.stderr_valid = fcntl(STDERR_FILENO, F_GETFD) != -1;
+
+	logopts = LOGERR_LOG | LOGERR_LOG_DATE | LOGERR_LOG_PID;
+	if (ctx.stderr_valid)
+		logopts |= LOGERR_ERR;
+
 	i = 0;
 	while ((opt = getopt_long(argc, argv,
 	    ctx.options & DHCPCD_PRINT_PIDFILE ? NOERR_IF_OPTS : IF_OPTS,
@@ -1979,6 +1986,8 @@ main(int argc, char **argv)
 	ctx.ifc = argc - optind;
 	ctx.ifv = argv + optind;
 
+	rt_init(&ctx);
+
 	ifo = read_config(&ctx, NULL, NULL, NULL);
 	if (ifo == NULL) {
 		if (ctx.options & DHCPCD_PRINT_PIDFILE)
@@ -2256,12 +2265,13 @@ printpidfile:
 	}
 
 	loginfox(PACKAGE "-" VERSION " starting");
-	if (freopen(_PATH_DEVNULL, "r", stdin) == NULL)
-		logerr("%s: freopen stdin", __func__);
+	if (ctx.stdin_valid && freopen(_PATH_DEVNULL, "w", stdin) == NULL)
+		logwarn("freopen stdin");
 
 #if defined(USE_SIGNALS) && !defined(THERE_IS_NO_FORK)
 	if (xsocketpair(AF_UNIX, SOCK_DGRAM | SOCK_CXNB, 0, fork_fd) == -1 ||
-	    xsocketpair(AF_UNIX, SOCK_DGRAM | SOCK_CXNB, 0, stderr_fd) == -1)
+	    (ctx.stderr_valid &&
+	    xsocketpair(AF_UNIX, SOCK_DGRAM | SOCK_CXNB, 0, stderr_fd) == -1))
 	{
 		logerr("socketpair");
 		goto exit_failure;
@@ -2284,15 +2294,18 @@ printpidfile:
 		 * Redirect stdout as well.
 		 * dhcpcd doesn't output via stdout, but something in
 		 * a called script might.
-		 *
-		 * Do NOT rights limit this fd as it will affect scripts.
-		 * For example, cmp reports insufficient caps on FreeBSD.
 		 */
-		if (dup2(stderr_fd[1], STDERR_FILENO) == -1 ||
-		    dup2(stderr_fd[1], STDOUT_FILENO) == -1)
-			logerr("dup2");
-		close(stderr_fd[0]);
-		close(stderr_fd[1]);
+		if (ctx.stderr_valid) {
+			if (dup2(stderr_fd[1], STDERR_FILENO) == -1 ||
+			    (ctx.stdout_valid &&
+			    dup2(stderr_fd[1], STDOUT_FILENO) == -1))
+				logerr("dup2");
+			close(stderr_fd[0]);
+			close(stderr_fd[1]);
+		} else if (ctx.stdout_valid) {
+			if (freopen(_PATH_DEVNULL, "w", stdout) == NULL)
+				logerr("freopen stdout");
+		}
 		if (setsid() == -1) {
 			logerr("%s: setsid", __func__);
 			goto exit_failure;
@@ -2312,10 +2325,9 @@ printpidfile:
 		break;
 	default:
 		ctx.options |= DHCPCD_FORKED; /* A lie */
+		setproctitle("[launcher]");
 		ctx.fork_fd = fork_fd[0];
 		close(fork_fd[1]);
-		ctx.stderr_fd = stderr_fd[0];
-		close(stderr_fd[1]);
 #ifdef PRIVSEP_RIGHTS
 		if (ps_rights_limit_fd(fork_fd[0]) == -1 ||
 		    ps_rights_limit_fd(stderr_fd[0]) == 1)
@@ -2324,10 +2336,21 @@ printpidfile:
 			goto exit_failure;
 		}
 #endif
-		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);
+
+		if (ctx.stderr_valid) {
+			ctx.stderr_fd = stderr_fd[0];
+			close(stderr_fd[1]);
+#ifdef PRIVSEP_RIGHTS
+			if (ps_rights_limit_fd(stderr_fd[0]) == 1) {
+				logerr("ps_rights_limit_fdpair");
+				goto exit_failure;
+			}
+#endif
+			if (ctx.stderr_valid)
+				eloop_event_add(ctx.eloop, ctx.stderr_fd,
+				    dhcpcd_stderr_cb, &ctx);
+		}
 		goto run_loop;
 	}