Do not fail password check if shadow password does not exist -

fall back to ordinary one

Reduced usage of functions returning datain static buffers.
(mostly passwd/group/shadow related):

function                                             old     new   delta
correct_password                                     143     193     +50
sulogin_main                                         490     533     +43
adduser_main                                         732     774     +42
passwd_main                                         1875    1915     +40
addgroup_main                                        330     365     +35
bb_internal_getspnam                                  38       -     -38
bb_internal_fgetpwent                                 38       -     -38
bb_internal_fgetgrent                                 38       -     -38
static.resultbuf                                     168      88     -80
static.buffer                                       1872    1104    -768
------------------------------------------------------------------------------
(add/remove: 0/3 grow/shrink: 5/2 up/down: 210/-962)         Total: -752 bytes

1 files changed, 16 insertions, 11 deletions

diff --git a/libbb/correct_password.c b/libbb/correct_password.c
index d031b2109..c515b26af 100644
--- a/libbb/correct_password.c
+++ b/libbb/correct_password.c
@@ -37,19 +37,24 @@
 
 int correct_password(const struct passwd *pw)
 {
-        char *unencrypted, *encrypted, *correct;
+        char *unencrypted, *encrypted;
+        const char *correct;
+#if ENABLE_FEATURE_SHADOWPASSWDS
+        /* Using _r function to avoid pulling in static buffers */
+        struct spwd spw;
+        struct spwd *result;
+        char buffer[256];
+#endif
 
-#ifdef CONFIG_FEATURE_SHADOWPASSWDS
+        correct = pw->pw_passwd;
+#if ENABLE_FEATURE_SHADOWPASSWDS
         if (LONE_CHAR(pw->pw_passwd, 'x') || LONE_CHAR(pw->pw_passwd, '*')) {
-                struct spwd *sp = getspnam(pw->pw_name);
-
-                if (!sp)
-                        bb_error_msg_and_die("no valid shadow password");
-
-                correct = sp->sp_pwdp;
-        } else
+                if (getspnam_r(pw->pw_name, &spw, buffer, sizeof(buffer), &result))
+                        bb_error_msg("no valid shadow password, checking ordinary one");
+                else
+                        correct = spw.sp_pwdp;
+        }
 #endif
-                correct = pw->pw_passwd;
 
         if (!correct || correct[0] == '\0')
                 return 1;
@@ -60,5 +65,5 @@ int correct_password(const struct passwd *pw)
         }
         encrypted = crypt(unencrypted, correct);
         memset(unencrypted, 0, strlen(unencrypted));
-        return (!strcmp(encrypted, correct)) ? 1 : 0;
+        return strcmp(encrypted, correct) == 0;
 }