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authorDenys Vlasenko <vda.linux@googlemail.com>2017-04-13 10:57:04 (GMT)
committerDenys Vlasenko <vda.linux@googlemail.com>2017-04-13 10:57:04 (GMT)
commit335681ca8e39144fa19814f7ba10d0fe760e4055 (patch)
tree81c20a0be3daab564c842f510126037bf2331ab2
parent517a82c5b6b5e279f3e96a6774445a2952ca312b (diff)
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su: FEATURE_SU_BLANK_PW_NEEDS_SECURE_TTY
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. Based on patch by Kaarle Ritvanen <kaarle.ritvanen@datakunkku.fi> Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
-rw-r--r--include/libbb.h1
-rw-r--r--libbb/correct_password.c4
-rw-r--r--loginutils/su.c27
3 files changed, 25 insertions, 7 deletions
diff --git a/include/libbb.h b/include/libbb.h
index 6b33ffa..b889dd7 100644
--- a/include/libbb.h
+++ b/include/libbb.h
@@ -1486,6 +1486,7 @@ int check_securetty(const char *short_tty) FAST_FUNC;
#else
static ALWAYS_INLINE int check_securetty(const char *short_tty UNUSED_PARAM) { return 1; }
#endif
+#define CHECKPASS_PW_HAS_EMPTY_PASSWORD 2
int check_password(const struct passwd *pw, const char *plaintext) FAST_FUNC;
int ask_and_check_password_extended(const struct passwd *pw, int timeout, const char *prompt) FAST_FUNC;
int ask_and_check_password(const struct passwd *pw) FAST_FUNC;
diff --git a/libbb/correct_password.c b/libbb/correct_password.c
index 513c930..3436edc 100644
--- a/libbb/correct_password.c
+++ b/libbb/correct_password.c
@@ -88,7 +88,7 @@ int FAST_FUNC check_password(const struct passwd *pw, const char *plaintext)
/* Ask the user for a password.
- * Return 1 without asking if PW has an empty password.
+ * Return CHECKPASS_PW_HAS_EMPTY_PASSWORD without asking if PW has an empty password.
* Return -1 on EOF, error while reading input, or timeout.
* Return 1 if the user gives the correct password for entry PW,
* 0 if not.
@@ -105,7 +105,7 @@ int FAST_FUNC ask_and_check_password_extended(const struct passwd *pw,
pw_pass = get_passwd(pw, buffer);
if (!pw_pass[0]) /* empty password field? */
- return 1;
+ return CHECKPASS_PW_HAS_EMPTY_PASSWORD;
plaintext = bb_ask(STDIN_FILENO, timeout, prompt);
if (!plaintext) {
diff --git a/loginutils/su.c b/loginutils/su.c
index d04b85f..f2cd799 100644
--- a/loginutils/su.c
+++ b/loginutils/su.c
@@ -23,6 +23,11 @@
//config: bool "If user's shell is not in /etc/shells, disallow -s PROG"
//config: default y
//config: depends on SU
+//config:
+//config:config FEATURE_SU_BLANK_PW_NEEDS_SECURE_TTY
+//config: bool "Disallow blank passwords from TTYs other than specified in /etc/securetty"
+//config: default n
+//config: depends on SU
//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))
@@ -79,6 +84,7 @@ int su_main(int argc UNUSED_PARAM, char **argv)
char user_buf[64];
#endif
const char *old_user;
+ int r;
/* Note: we don't use "'+': stop at first non-option" idiom here.
* For su, "SCRIPT ARGS" or "-c CMD ARGS" do not stop option parsing:
@@ -99,6 +105,11 @@ 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_SYSLOG) {
/* The utmp entry (via getlogin) is probably the best way to
* identify the user, especially if someone su's from a su-shell.
@@ -112,20 +123,26 @@ 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) {
+ r = 1;
+ if (cur_uid != 0)
+ r = ask_and_check_password(pw);
+ if (r > 0) {
+ if (ENABLE_FEATURE_SU_BLANK_PW_NEEDS_SECURE_TTY
+ && r == CHECKPASS_PW_HAS_EMPTY_PASSWORD
+ && !check_securetty(tty)
+ ) {
+ goto fail;
+ }
if (ENABLE_FEATURE_SU_SYSLOG)
syslog(LOG_NOTICE, "%c %s %s:%s",
'+', tty, old_user, opt_username);
} else {
+ fail:
if (ENABLE_FEATURE_SU_SYSLOG)
syslog(LOG_NOTICE, "%c %s %s:%s",
'-', tty, old_user, opt_username);