Bug#31669 Buffer overflow in mysql_change_user()

The problem is that when copying the supplied username and
database, no bounds checking is performed on the fixed-length
buffer. A sufficiently large (> 512) user string can easily
cause stack corruption. Since this API can be used from PHP
and other programs, this is a serious problem.

The solution is to increase the buffer size to the accepted
size in similar functions and perform bounds checking when
copying the username and database.

1 files changed, 4 insertions, 3 deletions

diff --git a/libmysql/libmysql.c b/libmysql/libmysql.c
index c7bdfc4c42c..5c015bd6b0f 100644
--- a/libmysql/libmysql.c
+++ b/libmysql/libmysql.c
@@ -706,7 +706,8 @@ int cli_read_change_user_result(MYSQL *mysql, char *buff, const char *passwd)
 my_bool	STDCALL mysql_change_user(MYSQL *mysql, const char *user,
 				  const char *passwd, const char *db)
 {
-  char buff[512],*end=buff;
+  char buff[USERNAME_LENGTH+SCRAMBLED_PASSWORD_CHAR_LENGTH+NAME_LEN+2];
+  char *end= buff;
   int rc;
   DBUG_ENTER("mysql_change_user");
 
@@ -716,7 +717,7 @@ my_bool	STDCALL mysql_change_user(MYSQL *mysql, const char *user,
     passwd="";
 
   /* Store user into the buffer */
-  end=strmov(end,user)+1;
+  end= strmake(end, user, USERNAME_LENGTH) + 1;
 
   /* write scrambled password according to server capabilities */
   if (passwd[0])
@@ -736,7 +737,7 @@ my_bool	STDCALL mysql_change_user(MYSQL *mysql, const char *user,
   else
     *end++= '\0';                               /* empty password */
   /* Add database if needed */
-  end= strmov(end, db ? db : "") + 1;
+  end= strmake(end, db ? db : "", NAME_LEN) + 1;
 
   /* Write authentication package */
   simple_command(mysql,COM_CHANGE_USER, buff,(ulong) (end-buff),1);