Bug#28478 - Improper key_cache_block_size corrupts MyISAM tables

Setting a key_cache_block_size which is not a power of 2
could corrupt MyISAM tables.

A couple of computations in the key cache code use bit
operations which do only work if key_cache_block_size
is a power of 2.

Replaced bit operations by arithmetic operations
to make key cache able to handle block sizes that are
not a power of 2.

include/keycache.h

@@ -46,7 +46,6 @@ typedef struct st_key_cache
   my_bool key_cache_inited;
   my_bool resize_in_flush;       /* true during flush of resize operation    */
   my_bool can_be_used;           /* usage of cache for read/write is allowed */
-  uint key_cache_shift;
   ulong key_cache_mem_size;      /* specified size of the cache memory       */
   uint key_cache_block_size;     /* size of the page buffer of a cache block */
   ulong min_warm_blocks;         /* min number of warm blocks;               */

mysql-test/r/key_cache.result

@@ -341,3 +341,30 @@ Warning	1438	Cannot drop default keycache
 select @@global.key_buffer_size;
 @@global.key_buffer_size
 2097152
+SET @bug28478_key_cache_block_size= @@global.key_cache_block_size;
+SET GLOBAL key_cache_block_size= 1536;
+CREATE TABLE t1 (
+id BIGINT NOT NULL AUTO_INCREMENT PRIMARY KEY,
+c1 CHAR(150),
+c2 CHAR(150),
+c3 CHAR(150),
+KEY(c1, c2, c3)
+) ENGINE= MyISAM;
+INSERT INTO t1 (c1, c2, c3) VALUES
+('a', 'b', 'c'), ('b', 'c', 'd'), ('c', 'd', 'e'), ('d', 'e', 'f'),
+('e', 'f', 'g'), ('f', 'g', 'h'), ('g', 'h', 'i'), ('h', 'i', 'j'),
+('i', 'j', 'k'), ('j', 'k', 'l'), ('k', 'l', 'm'), ('l', 'm', 'n'),
+('m', 'n', 'o'), ('n', 'o', 'p'), ('o', 'p', 'q'), ('p', 'q', 'r'),
+('q', 'r', 's'), ('r', 's', 't'), ('s', 't', 'u'), ('t', 'u', 'v'),
+('u', 'v', 'w'), ('v', 'w', 'x'), ('w', 'x', 'y'), ('x', 'y', 'z');
+INSERT INTO t1 (c1, c2, c3) SELECT c1, c2, c3 from t1;
+INSERT INTO t1 (c1, c2, c3) SELECT c1, c2, c3 from t1;
+INSERT INTO t1 (c1, c2, c3) SELECT c1, c2, c3 from t1;
+CHECK TABLE t1;
+Table	Op	Msg_type	Msg_text
+test.t1	check	status	OK
+SHOW VARIABLES LIKE 'key_cache_block_size';
+Variable_name	Value
+key_cache_block_size	1536
+SET GLOBAL key_cache_block_size= @bug28478_key_cache_block_size;
+DROP TABLE t1;

mysql-test/t/key_cache.test

@@ -219,4 +219,31 @@ set global key_cache_block_size= @my_key_cache_block_size;
 set @@global.key_buffer_size=0;
 select @@global.key_buffer_size;
 
+#
+# Bug#28478 - Improper key_cache_block_size corrupts MyISAM tables
+#
+SET @bug28478_key_cache_block_size= @@global.key_cache_block_size;
+SET GLOBAL key_cache_block_size= 1536;
+CREATE TABLE t1 (
+  id BIGINT NOT NULL AUTO_INCREMENT PRIMARY KEY,
+  c1 CHAR(150),
+  c2 CHAR(150),
+  c3 CHAR(150),
+  KEY(c1, c2, c3)
+  ) ENGINE= MyISAM;
+INSERT INTO t1 (c1, c2, c3) VALUES
+  ('a', 'b', 'c'), ('b', 'c', 'd'), ('c', 'd', 'e'), ('d', 'e', 'f'),
+  ('e', 'f', 'g'), ('f', 'g', 'h'), ('g', 'h', 'i'), ('h', 'i', 'j'),
+  ('i', 'j', 'k'), ('j', 'k', 'l'), ('k', 'l', 'm'), ('l', 'm', 'n'),
+  ('m', 'n', 'o'), ('n', 'o', 'p'), ('o', 'p', 'q'), ('p', 'q', 'r'),
+  ('q', 'r', 's'), ('r', 's', 't'), ('s', 't', 'u'), ('t', 'u', 'v'),
+  ('u', 'v', 'w'), ('v', 'w', 'x'), ('w', 'x', 'y'), ('x', 'y', 'z');
+INSERT INTO t1 (c1, c2, c3) SELECT c1, c2, c3 from t1;
+INSERT INTO t1 (c1, c2, c3) SELECT c1, c2, c3 from t1;
+INSERT INTO t1 (c1, c2, c3) SELECT c1, c2, c3 from t1;
+CHECK TABLE t1;
+SHOW VARIABLES LIKE 'key_cache_block_size';
+SET GLOBAL key_cache_block_size= @bug28478_key_cache_block_size;
+DROP TABLE t1;
+
 # End of 4.1 tests

mysys/mf_keycache.c

@@ -173,7 +173,7 @@ static void test_key_cache(KEY_CACHE *keycache,
 #endif
 
 #define KEYCACHE_HASH(f, pos)                                                 \
-(((ulong) ((pos) >> keycache->key_cache_shift)+                               \
+(((ulong) ((pos) / keycache->key_cache_block_size) +                          \
                                      (ulong) (f)) & (keycache->hash_entries-1))
 #define FILE_HASH(f)                 ((uint) (f) & (CHANGED_BLOCKS_HASH-1))
 
@@ -329,7 +329,6 @@ int init_key_cache(KEY_CACHE *keycache, uint key_cache_block_size,
 
   keycache->key_cache_mem_size= use_mem;
   keycache->key_cache_block_size= key_cache_block_size;
-  keycache->key_cache_shift= my_bit_log2(key_cache_block_size);
   DBUG_PRINT("info", ("key_cache_block_size: %u",
 		      key_cache_block_size));
 
@@ -352,7 +351,7 @@ int init_key_cache(KEY_CACHE *keycache, uint key_cache_block_size,
 		       ALIGN_SIZE(hash_links * sizeof(HASH_LINK)) +
 		       ALIGN_SIZE(sizeof(HASH_LINK*) *
                                   keycache->hash_entries))) +
-	     ((ulong) blocks << keycache->key_cache_shift) > use_mem)
+	     ((ulong) blocks * keycache->key_cache_block_size) > use_mem)
         blocks--;
       /* Allocate memory for cache page buffers */
       if ((keycache->block_mem=
@@ -1807,7 +1806,7 @@ byte *key_cache_read(KEY_CACHE *keycache,
     uint status;
     int page_st;
 
-    offset= (uint) (filepos & (keycache->key_cache_block_size-1));
+    offset= (uint) (filepos % keycache->key_cache_block_size);
     /* Read data in key_cache_block_size increments */
     do
     {
@@ -1946,7 +1945,7 @@ int key_cache_insert(KEY_CACHE *keycache,
     int error;
     uint offset;
 
-    offset= (uint) (filepos & (keycache->key_cache_block_size-1));
+    offset= (uint) (filepos % keycache->key_cache_block_size);
     do
     {
       keycache_pthread_mutex_lock(&keycache->cache_lock);
@@ -2081,7 +2080,7 @@ int key_cache_write(KEY_CACHE *keycache,
     int page_st;
     uint offset;
 
-    offset= (uint) (filepos & (keycache->key_cache_block_size-1));
+    offset= (uint) (filepos % keycache->key_cache_block_size);
     do
     {
       keycache_pthread_mutex_lock(&keycache->cache_lock);