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

1 files changed, 14 insertions, 13 deletions

diff --git a/loginutils/passwd.c b/loginutils/passwd.c
index 99afde2..0842b71 100644
--- a/loginutils/passwd.c
+++ b/loginutils/passwd.c
@@ -93,11 +93,9 @@ int passwd_main(int argc, char **argv)
 	uid_t myuid;
 	struct rlimit rlimit_fsize;
 	char c;
-
 #if ENABLE_FEATURE_SHADOWPASSWDS
 	/* Using _r function to avoid pulling in static buffers */
 	struct spwd spw;
-	struct spwd *result;
 	char buffer[256];
 #endif
 
@@ -128,16 +126,19 @@ int passwd_main(int argc, char **argv)
 	}
 
 #if ENABLE_FEATURE_SHADOWPASSWDS
-	/* getspnam_r() can lie! Even if user isn't in shadow, it can
-	 * return success (pwd field was seen set to "!" in this case) */
-	if (getspnam_r(pw->pw_name, &spw, buffer, sizeof(buffer), &result)
-	 || LONE_CHAR(spw.sp_pwdp, '!')) {
-		/* LOGMODE_BOTH */
-		bb_error_msg("no record of %s in %s, using %s",
-				name, bb_path_shadow_file,
-				bb_path_passwd_file);
-	} else {
-		pw->pw_passwd = 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;
+		if (getspnam_r(pw->pw_name, &spw, buffer, sizeof(buffer), &result)
+		 || !result || strcmp(result->sp_namp, pw->pw_name) != 0) {
+			/* LOGMODE_BOTH */
+			bb_error_msg("no record of %s in %s, using %s",
+					name, bb_path_shadow_file,
+					bb_path_passwd_file);
+		} else {
+			pw->pw_passwd = result->sp_pwdp;
+		}
 	}
 #endif
 
@@ -161,7 +162,7 @@ int passwd_main(int argc, char **argv)
 		newp = xasprintf("!%s", pw->pw_passwd);
 	} else if (opt & OPT_unlock) {
 		if (c) goto skip; /* not '!' */
-		/* pw->pw_passwd pints to static storage,
+		/* pw->pw_passwd points to static storage,
 		 * strdup'ing to avoid nasty surprizes */
 		newp = xstrdup(&pw->pw_passwd[1]);
 	} else if (opt & OPT_delete) {