login: clear dangerous environment variables if started by non-root

include/libbb.h

@@ -623,6 +623,8 @@ enum {
 #endif
 void bb_daemonize_or_rexec(int flags, char **argv);
 void bb_sanitize_stdio(void);
+/* Clear dangerous stuff, set PATH */
+void sanitize_env_for_suid(void);
 
 
 extern const char *opt_complementary;

libbb/login.c

@@ -99,3 +99,29 @@ void print_login_prompt(void)
 	fputs(LOGIN, stdout);
 	fflush(stdout);
 }
+
+/* Clear dangerous stuff, set PATH */
+static const char forbid[] ALIGN1 =
+	"ENV" "\0"
+	"BASH_ENV" "\0"
+	"HOME" "\0"
+	"IFS" "\0"
+	"SHELL" "\0"
+	"LD_LIBRARY_PATH" "\0"
+	"LD_PRELOAD" "\0"
+	"LD_TRACE_LOADED_OBJECTS" "\0"
+	"LD_BIND_NOW" "\0"
+	"LD_AOUT_LIBRARY_PATH" "\0"
+	"LD_AOUT_PRELOAD" "\0"
+	"LD_NOWARN" "\0"
+	"LD_KEEPDIR" "\0";
+
+void sanitize_env_for_suid(void)
+{
+	const char *p = forbid;
+	do {
+		unsetenv(p);
+		p += strlen(p) + 1;
+	} while (*p);
+	putenv((char*)bb_PATH_root_path);
+}

loginutils/login.c

@@ -201,7 +201,7 @@ static void motd(void)
 	int fd;
 
 	fd = open(bb_path_motd_file, O_RDONLY);
-	if (fd) {
+	if (fd >= 0) {
 		fflush(stdout);
 		bb_copyfd_eof(fd, STDOUT_FILENO);
 		close(fd);
@@ -216,6 +216,10 @@ static void alarm_handler(int sig ATTRIBUTE_UNUSED)
 	ndelay_on(1);
 	ndelay_on(2);
 	printf("\r\nLogin timed out after %d seconds\r\n", TIMEOUT);
+	/* unix API is brain damaged regarding O_NONBLOCK,
+	 * we should undo it, or else we can affect other processes */
+	ndelay_off(1);
+	ndelay_off(2);
 	exit(EXIT_SUCCESS);
 }
 
@@ -254,6 +258,11 @@ int login_main(int argc, char **argv)
 	 * and any extra open fd's are closed.
 	 * (The name of the function is misleading. Not daemonizing here.) */
 	bb_daemonize_or_rexec(DAEMON_ONLY_SANITIZE | DAEMON_CLOSE_EXTRA_FDS, NULL);
+	/* More of suid paranoia if called by non-root */
+	if (!amroot) {
+	        /* Clear dangerous stuff, set PATH */
+		sanitize_env_for_suid();
+	}
 
 	opt = getopt32(argv, "f:h:p", &opt_user, &opt_host);
 	if (opt & LOGIN_OPT_f) {
@@ -411,7 +420,8 @@ int login_main(int argc, char **argv)
 	fchown(0, pw->pw_uid, pw->pw_gid);
 	fchmod(0, 0600);
 
-	if (ENABLE_LOGIN_SCRIPTS) {
+	/* We trust environment only if we run by root */
+	if (ENABLE_LOGIN_SCRIPTS && amroot) {
 		char *t_argv[2];
 
 		t_argv[0] = getenv("LOGIN_PRE_SUID_SCRIPT");

loginutils/sulogin.c

@@ -9,22 +9,6 @@
 
 #include "libbb.h"
 
-static const char forbid[] ALIGN1 =
-	"ENV" "\0"
-	"BASH_ENV" "\0"
-	"HOME" "\0"
-	"IFS" "\0"
-	"PATH" "\0"
-	"SHELL" "\0"
-	"LD_LIBRARY_PATH" "\0"
-	"LD_PRELOAD" "\0"
-	"LD_TRACE_LOADED_OBJECTS" "\0"
-	"LD_BIND_NOW" "\0"
-	"LD_AOUT_LIBRARY_PATH" "\0"
-	"LD_AOUT_PRELOAD" "\0"
-	"LD_NOWARN" "\0"
-	"LD_KEEPDIR" "\0";
-
 //static void catchalarm(int ATTRIBUTE_UNUSED junk)
 //{
 //	exit(EXIT_FAILURE);
@@ -37,7 +21,6 @@ int sulogin_main(int argc, char **argv)
 	char *cp;
 	int timeout = 0;
 	char *timeout_arg;
-	const char *p;
 	struct passwd *pwd;
 	const char *shell;
 #if ENABLE_FEATURE_SHADOWPASSWDS
@@ -66,12 +49,8 @@ int sulogin_main(int argc, char **argv)
 		bb_error_msg_and_die("not a tty");
 	}
 
-	/* Clear out anything dangerous from the environment */
+	/* Clear dangerous stuff, set PATH */
-	p = forbid;
+	sanitize_env_for_suid();
-	do {
-		unsetenv(p);
-		p += strlen(p) + 1;
-	} while (*p);
 
 // bb_askpass() already handles this
 //	signal(SIGALRM, catchalarm);