MDEV-28481 SIGSEGV in Lex_charset_collation_st::find_bin_collation

mysql-test/main/ctype_filename.result

@@ -133,3 +133,22 @@ a	c
 DROP TABLE t1;
 SET NAMES utf8;
 # End of 10.5 tests
+#
+# Start of 10.9 tests
+#
+#
+# MDEV-28481 SIGSEGV in Lex_charset_collation_st::find_bin_collation
+#
+SET SESSION collation_server=filename;
+CREATE DATABASE db1;
+USE db1;
+CREATE TABLE t (c CHAR BINARY);
+ERROR HY000: Unknown collation: 'filename_bin'
+DROP DATABASE db1;
+USE test;
+SET NAMES latin1;
+CREATE TABLE t1 (c CHAR BINARY) CHARACTER SET filename;
+ERROR HY000: Unknown collation: 'filename_bin'
+#
+# End of 10.9 tests
+#

mysql-test/main/ctype_filename.test

@@ -139,3 +139,27 @@ SET NAMES utf8;
 --enable_ps_protocol
 
 --echo # End of 10.5 tests
+
+--echo #
+--echo # Start of 10.9 tests
+--echo #
+
+--echo #
+--echo # MDEV-28481 SIGSEGV in Lex_charset_collation_st::find_bin_collation
+--echo #
+
+SET SESSION collation_server=filename;
+CREATE DATABASE db1;
+USE db1;
+--error ER_UNKNOWN_COLLATION
+CREATE TABLE t (c CHAR BINARY);
+DROP DATABASE db1;
+USE test;
+SET NAMES latin1;
+
+--error ER_UNKNOWN_COLLATION
+CREATE TABLE t1 (c CHAR BINARY) CHARACTER SET filename;
+
+--echo #
+--echo # End of 10.9 tests
+--echo #

sql/lex_charset.cc

@@ -41,10 +41,11 @@ CHARSET_INFO *Lex_charset_collation_st::find_bin_collation(CHARSET_INFO *cs)
     return cs;
 
   // CREATE TABLE t1 (a CHAR(10) BINARY) CHARACTER SET utf8mb4;
+  const LEX_CSTRING &cs_name= cs->cs_name;
   if (!(cs= get_charset_by_csname(cs->cs_name.str, MY_CS_BINSORT, MYF(0))))
   {
     char tmp[65];
-    strxnmov(tmp, sizeof(tmp)-1, cs->cs_name.str, "_bin", NULL);
+    strxnmov(tmp, sizeof(tmp)-1, cs_name.str, "_bin", NULL);
     my_error(ER_UNKNOWN_COLLATION, MYF(0), tmp);
   }
   return cs;