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From d9c09138d91566af49ef8179d9995c84294e2486 Mon Sep 17 00:00:00 2001
From: Kaarle Ritvanen <kaarle.ritvanen@datakunkku.fi>
Date: Thu, 5 Nov 2015 16:27:36 +0200
Subject: [PATCH 10/12] su: FEATURE_SU_NULLOK_SECURE
When this feature is enabled, blank passwords are not accepted by su
unless the user is on a secure TTY defined in /etc/securetty. This
resembles the default PAM configuration of some Linux distros which
specify the nullok_secure option for pam_unix.so.
---
loginutils/su.c | 18 +++++++++++++-----
1 file changed, 13 insertions(+), 5 deletions(-)
diff --git a/loginutils/su.c b/loginutils/su.c
index 24ffbde86..086445243 100644
--- a/loginutils/su.c
+++ b/loginutils/su.c
@@ -24,6 +24,11 @@
//config: bool "Enable su to check user's shell to be listed in /etc/shells"
//config: depends on SU
//config: default y
+//config:config FEATURE_SU_NULLOK_SECURE
+//config: bool "Disallow blank passwords from TTYs other than specified in /etc/securetty"
+//config: depends on SU
+//config: default n
+
//applet:/* Needs to be run by root or be suid root - needs to change uid and gid: */
//applet:IF_SU(APPLET(su, BB_DIR_BIN, BB_SUID_REQUIRE))
@@ -76,6 +81,7 @@ int su_main(int argc UNUSED_PARAM, char **argv)
struct passwd *pw;
uid_t cur_uid = getuid();
const char *tty;
+ int allow_blank = 1;
#if ENABLE_FEATURE_UTMP
char user_buf[64];
#endif
@@ -100,6 +106,12 @@ int su_main(int argc UNUSED_PARAM, char **argv)
argv++;
}
+ tty = xmalloc_ttyname(STDIN_FILENO);
+ if (!tty) tty = "none";
+ tty = skip_dev_pfx(tty);
+
+ if (ENABLE_FEATURE_SU_NULLOK_SECURE) allow_blank = check_securetty(tty);
+
if (ENABLE_FEATURE_SU_SYSLOG) {
/* The utmp entry (via getlogin) is probably the best way to
* identify the user, especially if someone su's from a su-shell.
@@ -113,16 +125,12 @@ int su_main(int argc UNUSED_PARAM, char **argv)
pw = getpwuid(cur_uid);
old_user = pw ? xstrdup(pw->pw_name) : "";
}
- tty = xmalloc_ttyname(2);
- if (!tty) {
- tty = "none";
- }
openlog(applet_name, 0, LOG_AUTH);
}
pw = xgetpwnam(opt_username);
- if (cur_uid == 0 || ask_and_check_password(pw) > 0) {
+ if (cur_uid == 0 || ask_and_check_password_extended(pw, 0, allow_blank, "Password: ") > 0) {
if (ENABLE_FEATURE_SU_SYSLOG)
syslog(LOG_NOTICE, "%c %s %s:%s",
'+', tty, old_user, opt_username);
--
2.11.0
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