MDEV-17964: Assertion `status == 0' failed in add_role_user_mapping_action

This happens upon CREATE USER and DROP ROLE.

The underlying problem is that our HASH implementation shuffles elements
around when performing an update or delete. This means that when doing a
scan through the HASH table by index, in search of elements to delete or
update one must restart the scan to make sure nothing is missed if at least
one delete / update happened.

More specifically, what happened in this case:
The hash has 131 element, DROP ROLE removes the element
[119]. Its [119]->next was element [129], so [129] is moved to [119].
Now we need to compact the hash, removing the last element [130]. It
gets one bit off its hash value and becomes element [2]. The existing
element [2] is moved to [129], and old [130] is moved to [2].

We cannot simply move [130] to [129] and make [2]->next=130, it won't
work if [2] is itself in the collision list and doesn't belong in [2].

The handle_grant_struct code assumed that it is safe to continue by only
reexamining the currently modified / deleted element index, but that is
not true.

Missing to delete an element in the hash triggered the assertion in
the test case. DROP ROLE would not clear all necessary role->role or
role->user mappings.

To fix the problem we ensure that the scan is restarted, only if an
element was deleted / updated, similar to how bubble-sort keeps sorting
until it finds no more elements to swap.

mysql-test/suite/roles/rebuild_role_grants.result

@@ -65,3 +65,269 @@ drop role look, isp, xxx, ppp;
 connection default;
 disconnect con1;
 drop user nnnn@'%';
+CREATE USER u@localhost;
+CREATE ROLE r1;
+CREATE ROLE r2;
+CREATE ROLE r3;
+CREATE ROLE r4;
+CREATE ROLE r5;
+CREATE ROLE r6;
+CREATE ROLE r7;
+CREATE ROLE r8;
+CREATE ROLE r9;
+CREATE ROLE r10;
+CREATE ROLE r11;
+CREATE ROLE r12;
+CREATE ROLE r13;
+CREATE ROLE r14;
+CREATE ROLE r15;
+CREATE ROLE r16;
+CREATE ROLE r17;
+CREATE ROLE r18;
+CREATE ROLE r19;
+CREATE ROLE r20;
+CREATE ROLE r21;
+CREATE ROLE r22;
+CREATE ROLE r23;
+CREATE ROLE r24;
+CREATE ROLE r25;
+CREATE ROLE r26;
+CREATE ROLE r27;
+CREATE ROLE r28;
+CREATE ROLE r29;
+CREATE ROLE r30;
+CREATE ROLE r31;
+CREATE ROLE r32;
+CREATE ROLE r33;
+CREATE ROLE r34;
+CREATE ROLE r35;
+CREATE ROLE r36;
+CREATE ROLE r37;
+CREATE ROLE r38;
+CREATE ROLE r39;
+CREATE ROLE r40;
+CREATE ROLE r41;
+CREATE ROLE r42;
+CREATE ROLE r43;
+CREATE ROLE r44;
+CREATE ROLE r45;
+CREATE ROLE r46;
+CREATE ROLE r47;
+CREATE ROLE r48;
+CREATE ROLE r49;
+CREATE ROLE r50;
+CREATE ROLE r51;
+CREATE ROLE r52;
+CREATE ROLE r53;
+CREATE ROLE r54;
+CREATE ROLE r55;
+CREATE ROLE r56;
+CREATE ROLE r57;
+CREATE ROLE r58;
+CREATE ROLE r59;
+CREATE ROLE r60;
+CREATE ROLE r61;
+CREATE ROLE r62;
+CREATE ROLE r63;
+CREATE ROLE r64;
+CREATE ROLE r65;
+CREATE ROLE r66;
+CREATE ROLE r67;
+CREATE ROLE r68;
+CREATE ROLE r69;
+CREATE ROLE r70;
+CREATE ROLE r71;
+CREATE ROLE r72;
+CREATE ROLE r73;
+CREATE ROLE r74;
+CREATE ROLE r75;
+CREATE ROLE r76;
+CREATE ROLE r77;
+CREATE ROLE r78;
+CREATE ROLE r79;
+CREATE ROLE r80;
+CREATE ROLE r81;
+CREATE ROLE r82;
+CREATE ROLE r83;
+CREATE ROLE r84;
+CREATE ROLE r85;
+CREATE ROLE r86;
+CREATE ROLE r87;
+CREATE ROLE r88;
+CREATE ROLE r89;
+CREATE ROLE r90;
+CREATE ROLE r91;
+CREATE ROLE r92;
+CREATE ROLE r93;
+CREATE ROLE r94;
+CREATE ROLE r95;
+CREATE ROLE r96;
+CREATE ROLE r97;
+CREATE ROLE r98;
+CREATE ROLE r99;
+CREATE ROLE r100;
+CREATE ROLE r101;
+CREATE ROLE r102;
+CREATE ROLE r103;
+CREATE ROLE r104;
+CREATE ROLE r105;
+CREATE ROLE r106;
+CREATE ROLE r107;
+CREATE ROLE r108;
+CREATE ROLE r109;
+CREATE ROLE r110;
+CREATE ROLE r111;
+CREATE ROLE r112;
+CREATE ROLE r113;
+CREATE ROLE r114;
+CREATE ROLE r115;
+CREATE ROLE r116;
+CREATE ROLE r117;
+CREATE ROLE r118;
+CREATE ROLE r119;
+CREATE ROLE r120;
+CREATE ROLE r121;
+CREATE ROLE r122;
+CREATE ROLE r123;
+CREATE ROLE r124;
+CREATE ROLE r125;
+CREATE ROLE r126;
+CREATE ROLE r127;
+CREATE ROLE r128;
+CREATE ROLE n;
+CREATE ROLE d WITH ADMIN n;
+CREATE ROLE '%' WITH ADMIN u@localhost;
+DROP ROLE n;
+CREATE USER 't';
+DROP ROLE r1;
+DROP ROLE r2;
+DROP ROLE r3;
+DROP ROLE r4;
+DROP ROLE r5;
+DROP ROLE r6;
+DROP ROLE r7;
+DROP ROLE r8;
+DROP ROLE r9;
+DROP ROLE r10;
+DROP ROLE r11;
+DROP ROLE r12;
+DROP ROLE r13;
+DROP ROLE r14;
+DROP ROLE r15;
+DROP ROLE r16;
+DROP ROLE r17;
+DROP ROLE r18;
+DROP ROLE r19;
+DROP ROLE r20;
+DROP ROLE r21;
+DROP ROLE r22;
+DROP ROLE r23;
+DROP ROLE r24;
+DROP ROLE r25;
+DROP ROLE r26;
+DROP ROLE r27;
+DROP ROLE r28;
+DROP ROLE r29;
+DROP ROLE r30;
+DROP ROLE r31;
+DROP ROLE r32;
+DROP ROLE r33;
+DROP ROLE r34;
+DROP ROLE r35;
+DROP ROLE r36;
+DROP ROLE r37;
+DROP ROLE r38;
+DROP ROLE r39;
+DROP ROLE r40;
+DROP ROLE r41;
+DROP ROLE r42;
+DROP ROLE r43;
+DROP ROLE r44;
+DROP ROLE r45;
+DROP ROLE r46;
+DROP ROLE r47;
+DROP ROLE r48;
+DROP ROLE r49;
+DROP ROLE r50;
+DROP ROLE r51;
+DROP ROLE r52;
+DROP ROLE r53;
+DROP ROLE r54;
+DROP ROLE r55;
+DROP ROLE r56;
+DROP ROLE r57;
+DROP ROLE r58;
+DROP ROLE r59;
+DROP ROLE r60;
+DROP ROLE r61;
+DROP ROLE r62;
+DROP ROLE r63;
+DROP ROLE r64;
+DROP ROLE r65;
+DROP ROLE r66;
+DROP ROLE r67;
+DROP ROLE r68;
+DROP ROLE r69;
+DROP ROLE r70;
+DROP ROLE r71;
+DROP ROLE r72;
+DROP ROLE r73;
+DROP ROLE r74;
+DROP ROLE r75;
+DROP ROLE r76;
+DROP ROLE r77;
+DROP ROLE r78;
+DROP ROLE r79;
+DROP ROLE r80;
+DROP ROLE r81;
+DROP ROLE r82;
+DROP ROLE r83;
+DROP ROLE r84;
+DROP ROLE r85;
+DROP ROLE r86;
+DROP ROLE r87;
+DROP ROLE r88;
+DROP ROLE r89;
+DROP ROLE r90;
+DROP ROLE r91;
+DROP ROLE r92;
+DROP ROLE r93;
+DROP ROLE r94;
+DROP ROLE r95;
+DROP ROLE r96;
+DROP ROLE r97;
+DROP ROLE r98;
+DROP ROLE r99;
+DROP ROLE r100;
+DROP ROLE r101;
+DROP ROLE r102;
+DROP ROLE r103;
+DROP ROLE r104;
+DROP ROLE r105;
+DROP ROLE r106;
+DROP ROLE r107;
+DROP ROLE r108;
+DROP ROLE r109;
+DROP ROLE r110;
+DROP ROLE r111;
+DROP ROLE r112;
+DROP ROLE r113;
+DROP ROLE r114;
+DROP ROLE r115;
+DROP ROLE r116;
+DROP ROLE r117;
+DROP ROLE r118;
+DROP ROLE r119;
+DROP ROLE r120;
+DROP ROLE r121;
+DROP ROLE r122;
+DROP ROLE r123;
+DROP ROLE r124;
+DROP ROLE r125;
+DROP ROLE r126;
+DROP ROLE r127;
+DROP ROLE r128;
+DROP ROLE d;
+DROP ROLE '%';
+DROP USER 't';
+DROP USER u@localhost;

mysql-test/suite/roles/rebuild_role_grants.test

@@ -67,3 +67,34 @@ drop role look, isp, xxx, ppp;
 connection default;
 disconnect con1;
 drop user nnnn@'%';
+
+#
+# MDEV-17964 Assertion `status == 0' failed in add_role_user_mapping_action
+#            upon CREATE USER and DROP ROLE
+#
+CREATE USER u@localhost;
+
+--let $n= 1
+while ($n < 129)
+{
+  eval CREATE ROLE r$n;
+  inc $n;
+}
+
+CREATE ROLE n;
+CREATE ROLE d WITH ADMIN n;
+CREATE ROLE '%' WITH ADMIN u@localhost;
+DROP ROLE n;
+CREATE USER 't';
+
+--let $n= 1
+while ($n < 129)
+{
+  eval DROP ROLE r$n;
+  inc $n;
+}
+
+DROP ROLE d;
+DROP ROLE '%';
+DROP USER 't';
+DROP USER u@localhost;