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

4 files changed, 42 insertions, 25 deletions

diff --git a/include/libbb.h b/include/libbb.h
index 77c678cee..f79d80d7f 100644
--- a/include/libbb.h
+++ b/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;
diff --git a/libbb/login.c b/libbb/login.c
index 308e1bfed..1af3165b9 100644
--- a/libbb/login.c
+++ b/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);
+}
diff --git a/loginutils/login.c b/loginutils/login.c
index bddc0f533..c05edde36 100644
--- a/loginutils/login.c
+++ b/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");
diff --git a/loginutils/sulogin.c b/loginutils/sulogin.c
index f1545b78f..af457ef1e 100644
--- a/loginutils/sulogin.c
+++ b/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 */
-        p = forbid;
-        do {
-                unsetenv(p);
-                p += strlen(p) + 1;
-        } while (*p);
+        /* Clear dangerous stuff, set PATH */
+        sanitize_env_for_suid();
 
 // bb_askpass() already handles this
 //      signal(SIGALRM, catchalarm);