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List:       busybox
Subject:    Re: [PATCH] login: update UTMP before forking
From:       Markus Gothe <nietzsche () lysator ! liu ! se>
Date:       2020-05-09 11:33:41
Message-ID: sroelicml1vt6b0mh2dag9c0.1589024021318 () lysator ! liu ! se
[Download RAW message or body]

Nice catch!

//Markus

Sent from my BlackBerry - the most secure mobile device


	  Original Message  	


From: troglobit@gmail.com
Sent: May 9, 2020 13:04
To: busybox@busybox.net
Subject: [PATCH] login: update UTMP before forking


/bin/login updates the preliminary UTMP record created by /bin/getty for
$LOGNAME.  However, if the PID of login is not the same as getty, then
it will create a new entry.  This causes GLIBC getlogin(3) to return the
string 'LOGIN' (set by getty) instead of $LOGNAME.  This affects tools
like /usr/bin/logname but also various 3rd party PAM applications.

Signed-off-by: Joachim Nilsson <troglobit@gmail.com>
---
loginutils/login.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/loginutils/login.c b/loginutils/login.c
index 4e65b3a19..03301b3bd 100644
--- a/loginutils/login.c
+++ b/loginutils/login.c
@@ -525,6 +525,8 @@ int login_main(int argc UNUSED_PARAM, char **argv)
if (pw->pw_uid != 0)
die_if_nologin();

+ update_utmp(getpid(), USER_PROCESS, short_tty, username, run_by_root ? opt_host : NULL);
+
#if ENABLE_LOGIN_SESSION_AS_CHILD
child_pid = vfork();
if (child_pid != 0) {
@@ -546,8 +548,6 @@ int login_main(int argc UNUSED_PARAM, char **argv)
fchown(0, pw->pw_uid, pw->pw_gid);
fchmod(0, 0600);

- update_utmp(getpid(), USER_PROCESS, short_tty, username, run_by_root ? opt_host : NULL);
-
/* We trust environment only if we run by root */
if (ENABLE_LOGIN_SCRIPTS && run_by_root)
run_login_script(pw, full_tty);
--
2.25.1

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