[PATCH v2] auth: fix empty password authentication

[Vladimir Davydov <vdavydov.dev@gmail.com>]

We are supposed to authenticate guest user without a password. This
used to work before commit 076a842011e0 ("Permit empty passwords in
net.box"), when guest didn't have any password. Now it has an empty
password and the check in authenticate turns out to be broken, which
breaks assumptions made by certain connectors. This patch fixes the
check.

Closes #4327
---
https://github.com/tarantool/tarantool/issues/4327
https://github.com/tarantool/tarantool/tree/dv/gh-4327-fix-empty-password-auth

Changes in v2:
 - Don't change the way net.box treats absense of a password.
   Just fix the issue in question.

v1: https://www.freelists.org/post/tarantool-patches/PATCH-auth-fix-empty-password-authentication

 src/box/authentication.cc | 21 +++++++++++++++------
 1 file changed, 15 insertions(+), 6 deletions(-)

diff --git a/src/box/authentication.cc b/src/box/authentication.cc
index 811974cb..b0459a5b 100644
--- a/src/box/authentication.cc
+++ b/src/box/authentication.cc
@@ -33,8 +33,13 @@
 #include "session.h"
 #include "msgpuck.h"
 #include "error.h"
+#include "third_party/base64.h"
 
-static char zero_hash[SCRAMBLE_SIZE];
+/**
+ * chap-sha1 of empty string, i.e.
+ * base64_encode(sha1(sha1(""), 0)
+ */
+static const char *CHAP_SHA1_EMPTY_PASSWORD = "vhvewKp0tNyweZQ+cFKAlsyphfg=";
 
 void
 authenticate(const char *user_name, uint32_t len, const char *salt,
@@ -52,10 +57,14 @@ authenticate(const char *user_name, uint32_t len, const char *salt,
 	 * pooling.
 	 */
 	part_count = mp_decode_array(&tuple);
-	if (part_count == 0 && user->def->uid == GUEST &&
-	    memcmp(user->def->hash2, zero_hash, SCRAMBLE_SIZE) == 0) {
-		/* No password is set for GUEST, OK. */
-		goto ok;
+	if (part_count == 0 && user->def->uid == GUEST) {
+		char hash2[SCRAMBLE_SIZE];
+		base64_decode(CHAP_SHA1_EMPTY_PASSWORD, SCRAMBLE_BASE64_SIZE,
+			      hash2, SCRAMBLE_SIZE);
+		if (memcmp(user->def->hash2, hash2, SCRAMBLE_SIZE) == 0) {
+			/* Empty password is set, OK. */
+			goto ok;
+		}
 	}
 
 	access_check_session_xc(user);
@@ -90,11 +99,11 @@ authenticate(const char *user_name, uint32_t len, const char *salt,
 			diag_raise();
 		tnt_raise(ClientError, ER_PASSWORD_MISMATCH, user->def->name);
 	}
+ok:
 	/* check and run auth triggers on success */
 	if (! rlist_empty(&session_on_auth) &&
 	    session_run_on_auth_triggers(&auth_res) != 0)
 		diag_raise();
-ok:
 	credentials_init(&session->credentials, user->auth_token,
 			 user->def->uid);
 }
-- 
2.11.0