Re: Add login_tty

[Felix Janda <felix.janda@posteo.de>]

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Rich Felker wrote:
[..]
> I don't have any fundamental objection to this. It might be nice to
> review the forkpty code for errors it should be checking and make
> these improvements at the same time, though.

Ok, attached a proposed patch.

Felix

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From f1d88438a6d00defcf96562ef536a4af71827ee7 Mon Sep 17 00:00:00 2001
From: Felix Janda <felix.janda@posteo.de>
Date: Tue, 26 Aug 2014 18:36:23 +0200
Subject: [PATCH] split off login_tty() from forkpty() and clean up the latter

since after calling openpty() no new fds are needed, an fd limit
causes no problems.
---
 include/utmp.h       |  2 ++
 src/misc/forkpty.c   | 25 ++++---------------------
 src/misc/login_tty.c | 14 ++++++++++++++
 3 files changed, 20 insertions(+), 21 deletions(-)
 create mode 100644 src/misc/login_tty.c

diff --git a/include/utmp.h b/include/utmp.h
index e9ba23e..d3dcee7 100644
--- a/include/utmp.h
+++ b/include/utmp.h
@@ -43,6 +43,8 @@ void updwtmp(const char *, const struct utmp *);
 #define UTMP_FILENAME _PATH_UTMP
 #define WTMP_FILENAME _PATH_WTMP
 
+int login_tty(int);
+
 #ifdef __cplusplus
 }
 #endif
diff --git a/src/misc/forkpty.c b/src/misc/forkpty.c
index 07f8d01..007b369 100644
--- a/src/misc/forkpty.c
+++ b/src/misc/forkpty.c
@@ -1,37 +1,20 @@
 #include <pty.h>
+#include <utmp.h>
 #include <unistd.h>
-#include <sys/ioctl.h>
-#include <fcntl.h>
 
 int forkpty(int *m, char *name, const struct termios *tio, const struct winsize *ws)
 {
-	int s, t, i, istmp[3]={0};
+	int s;
 	pid_t pid;
 
 	if (openpty(m, &s, name, tio, ws) < 0) return -1;
 
-	/* Ensure before forking that we don't exceed fd limit */
-	for (i=0; i<3; i++) {
-		if (fcntl(i, F_GETFL) < 0) {
-			t = fcntl(s, F_DUPFD, i);
-			if (t<0) break;
-			else if (t!=i) close(t);
-			else istmp[i] = 1;
-		}
-	}
-	pid = i==3 ? fork() : -1;
+	pid = fork();
 	if (!pid) {
 		close(*m);
-		setsid();
-		ioctl(s, TIOCSCTTY, (char *)0);
-		dup2(s, 0);
-		dup2(s, 1);
-		dup2(s, 2);
-		if (s>2) close(s);
+		login_tty(s);
 		return 0;
 	}
-	for (i=0; i<3; i++)
-		if (istmp[i]) close(i);
 	close(s);
 	if (pid < 0) close(*m);
 	return pid;
diff --git a/src/misc/login_tty.c b/src/misc/login_tty.c
new file mode 100644
index 0000000..f0be0a0
--- /dev/null
+++ b/src/misc/login_tty.c
@@ -0,0 +1,14 @@
+#include <utmp.h>
+#include <sys/ioctl.h>
+#include <unistd.h>
+
+int login_tty(int fd)
+{
+	setsid();
+	if (ioctl(fd, TIOCSCTTY, (char *)0)) return -1;
+	dup2(fd, 0);
+	dup2(fd, 1);
+	dup2(fd, 2);
+	if (fd>2) close(fd);
+	return 0;
+}
-- 
1.8.5.5