From: Sami Kerola <kerolasa@iki.fi>
Date: Sat, 31 Oct 2015 19:21:16 +0000 (+0000)
Subject: agetty: fix chown(3), chmod(3) and open(3) race
X-Git-Tag: v2.28-rc1~282
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=c3a9f86fcd1977365bbbe9aaee36b02df9f330f5;p=thirdparty%2Futil-linux.git

agetty: fix chown(3), chmod(3) and open(3) race

Signed-off-by: Sami Kerola <kerolasa@iki.fi>
---

diff --git a/term-utils/agetty.c b/term-utils/agetty.c
index 0237b79d9e..a9c8785471 100644
--- a/term-utils/agetty.c
+++ b/term-utils/agetty.c
@@ -1004,23 +1004,23 @@ static void open_tty(char *tty, struct termios *tp, struct options *op)
 		     (int)sizeof(buf)) || (len < 0))
 			log_err(_("/dev/%s: cannot open as standard input: %m"), tty);
 
+		/* Open the tty as standard input. */
+		if ((fd = open(buf, O_RDWR|O_NOCTTY|O_NONBLOCK, 0)) < 0)
+			log_err(_("/dev/%s: cannot open as standard input: %m"), tty);
+
 		/*
 		 * There is always a race between this reset and the call to
 		 * vhangup() that s.o. can use to get access to your tty.
 		 * Linux login(1) will change tty permissions. Use root owner and group
 		 * with permission -rw------- for the period between getty and login.
 		 */
-		if (chown(buf, 0, gid) || chmod(buf, (gid ? 0620 : 0600))) {
+		if (fchown(fd, 0, gid) || fchmod(fd, (gid ? 0620 : 0600))) {
 			if (errno == EROFS)
 				log_warn("%s: %m", buf);
 			else
 				log_err("%s: %m", buf);
 		}
 
-		/* Open the tty as standard input. */
-		if ((fd = open(buf, O_RDWR|O_NOCTTY|O_NONBLOCK, 0)) < 0)
-			log_err(_("/dev/%s: cannot open as standard input: %m"), tty);
-
 		/* Sanity checks... */
 		if (fstat(fd, &st) < 0)
 			log_err("%s: %m", buf);