MDEV-16810 AddressSanitizer: stack-buffer-overflow in int10_to_str

truncate incorrect values in convert_period_to_month() so that
PERIOD_DIFF never returns a value outside of 2^23 range.

And, for safety, increase buffer sizes for int10_to_str
to be sufficienly big for any int10_to_str result.

mysql-test/r/func_time.result

@@ -2657,6 +2657,9 @@ SEC_TO_TIME(MAKEDATE(0,RAND(~0)))
 838:59:59
 Warnings:
 Warning	1292	Truncated incorrect time value: '20000101'
+SELECT PERIOD_DIFF(2018, AES_ENCRYPT('Rae Bareli', 'Rae Bareli'));
+PERIOD_DIFF(2018, AES_ENCRYPT('Rae Bareli', 'Rae Bareli'))
+24257
 #
 # End of 5.5 tests
 #

mysql-test/t/func_time.test

@@ -1629,6 +1629,10 @@ DO TO_DAYS(SEC_TO_TIME(MAKEDATE('',RAND(~('')))));
 SELECT TO_DAYS(SEC_TO_TIME(MAKEDATE(0,RAND(~0))));
 SELECT SEC_TO_TIME(MAKEDATE(0,RAND(~0)));
 
+#
+# MDEV-16810 AddressSanitizer: stack-buffer-overflow in int10_to_str
+#
+SELECT PERIOD_DIFF(2018, AES_ENCRYPT('Rae Bareli', 'Rae Bareli'));
 
 --echo #
 --echo # End of 5.5 tests

sql/protocol.cc

@@ -643,7 +643,7 @@ uchar *net_store_data(uchar *to, const uchar *from, size_t length)
 
 uchar *net_store_data(uchar *to,int32 from)
 {
-  char buff[20];
+  char buff[22];
   uint length=(uint) (int10_to_str(from,buff,10)-buff);
   to=net_store_length_fast(to,length);
   memcpy(to,buff,length);
@@ -1060,7 +1060,7 @@ bool Protocol_text::store_tiny(longlong from)
   DBUG_ASSERT(field_types == 0 || field_types[field_pos] == MYSQL_TYPE_TINY);
   field_pos++;
 #endif
-  char buff[20];
+  char buff[22];
   return net_store_data((uchar*) buff,
 			(size_t) (int10_to_str((int) from, buff, -10) - buff));
 }
@@ -1074,7 +1074,7 @@ bool Protocol_text::store_short(longlong from)
 	      field_types[field_pos] == MYSQL_TYPE_SHORT);
   field_pos++;
 #endif
-  char buff[20];
+  char buff[22];
   return net_store_data((uchar*) buff,
 			(size_t) (int10_to_str((int) from, buff, -10) -
                                   buff));
@@ -1089,7 +1089,7 @@ bool Protocol_text::store_long(longlong from)
               field_types[field_pos] == MYSQL_TYPE_LONG);
   field_pos++;
 #endif
-  char buff[20];
+  char buff[22];
   return net_store_data((uchar*) buff,
 			(size_t) (int10_to_str((long int)from, buff,
                                                (from <0)?-10:10)-buff));

sql/sql_time.cc

@@ -190,7 +190,7 @@ bool get_date_from_daynr(long daynr,uint *ret_year,uint *ret_month,
 ulong convert_period_to_month(ulong period)
 {
   ulong a,b;
-  if (period == 0)
+  if (period == 0 || period > 999912)
     return 0L;
   if ((a=period/100) < YY_PART_YEAR)
     a+=2000;