appletlib.c: make it actally follow _BB_SUID_ALWAYS rules

adduser: implement -S and code shrink / fix uid selection
*: sanitize getspnam_r use

   text    data     bss     dec     hex filename
 777042     974    9676  787692   c04ec busybox_old
 776883     974    9676  787533   c044d busybox_unstripped

2 files changed, 13 insertions, 11 deletions

diff --git a/libbb/appletlib.c b/libbb/appletlib.c
index 8b1ed8000..4bd60d049 100644
--- a/libbb/appletlib.c
+++ b/libbb/appletlib.c
@@ -459,10 +459,7 @@ static void check_suid(const struct bb_applet *applet)
                         if (sct->m_applet == applet)
                                 goto found;
                 }
-                /* default: drop all privileges */
-                xsetgid(rgid);
-                xsetuid(ruid);
-                return;
+                goto check_need_suid;
  found:
                 m = sct->m_mode;
                 if (sct->m_uid == ruid)
@@ -505,13 +502,13 @@ static void check_suid(const struct bb_applet *applet)
                 }
         }
 #endif
+ check_need_suid:
 #endif
-
         if (applet->need_suid == _BB_SUID_ALWAYS) {
                 /* Real uid is not 0. If euid isn't 0 too, suid bit
                  * is most probably not set on our executable */
                 if (geteuid())
-                        bb_error_msg_and_die("applet requires root privileges!");
+                        bb_error_msg_and_die("must be suid to work properly");
         } else if (applet->need_suid == _BB_SUID_NEVER) {
                 xsetgid(rgid);  /* drop all privileges */
                 xsetuid(ruid);
diff --git a/libbb/correct_password.c b/libbb/correct_password.c
index f1793cd17..96bb10e0b 100644
--- a/libbb/correct_password.c
+++ b/libbb/correct_password.c
@@ -40,6 +40,11 @@ int correct_password(const struct passwd *pw)
 {
         char *unencrypted, *encrypted;
         const char *correct;
+#if ENABLE_FEATURE_SHADOWPASSWDS
+        /* Using _r function to avoid pulling in static buffers */
+        struct spwd spw;
+        char buffer[256];
+#endif
 
         /* fake salt. crypt() can choke otherwise. */
         correct = "aa";
@@ -50,11 +55,11 @@ int correct_password(const struct passwd *pw)
         correct = pw->pw_passwd;
 #if ENABLE_FEATURE_SHADOWPASSWDS
         if ((correct[0] == 'x' || correct[0] == '*') && !correct[1]) {
-                /* Using _r function to avoid pulling in static buffers */
-                struct spwd spw;
-                struct spwd *result;
-                char buffer[256];
-                correct = (getspnam_r(pw->pw_name, &spw, buffer, sizeof(buffer), &result)) ? "aa" : spw.sp_pwdp;
+                /* getspnam_r may return 0 yet set result to NULL.
+                 * At least glibc 2.4 does this. Be extra paranoid here. */
+                struct spwd *result = NULL;
+                int r = getspnam_r(pw->pw_name, &spw, buffer, sizeof(buffer), &result);
+                correct = (r || !result) ? "aa" : result->sp_pwdp;
         }
 #endif