Minimize unsafe C functions usage - replace strcat() and strcpy() (and strncat() and strncpy()) with custom safe_strcat() and safe_strcpy() functions

The MariaDB code base uses strcat() and strcpy() in several
places. These are known to have memory safety issues and their usage is
discouraged. Common security scanners like Flawfinder flags them. In MariaDB we
should start using modern and safer variants on these functions.

This is similar to memory issues fixes in 19af1890b56c6c147c296479bb6a4ad00fa59dbb
and 9de9f105b5cb88249acc39af73d32af337d6fd5f but now replace use of strcat()
and strcpy() with safer options strncat() and strncpy().

However, add '\0' forcefully to make sure the result string is correct since
for these two functions it is not guaranteed what new string will be null-terminated.

Example:

    size_t dest_len = sizeof(g->Message);
    strncpy(g->Message, "Null json tree", dest_len); strncat(g->Message, ":",
    sizeof(g->Message) - strlen(g->Message)); size_t wrote_sz = strlen(g->Message);
    size_t cur_len = wrote_sz >= dest_len ? dest_len - 1 : wrote_sz;
    g->Message[cur_len] = '\0';

All new code of the whole pull request, including one or several files
that are either new files or modified ones, are contributed under the BSD-new
license. I am contributing on behalf of my employer Amazon Web Services

-- Reviewer and co-author Vicențiu Ciorbaru <vicentiu@mariadb.org>
-- Reviewer additions:
* The initial function implementation was flawed. Replaced with a simpler
  and also correct version.
* Simplified code by making use of snprintf instead of chaining strcat.
* Simplified code by removing dynamic string construction in the first
  place and using static strings if possible. See connect storage engine
  changes.

2 files changed, 9 insertions, 8 deletions

diff --git a/sql/mysql_install_db.cc b/sql/mysql_install_db.cc
index 9639051e93c..0baaff80ef6 100644
--- a/sql/mysql_install_db.cc
+++ b/sql/mysql_install_db.cc
@@ -243,7 +243,7 @@ static char *get_plugindir()
 {
   static char plugin_dir[2*MAX_PATH];
   get_basedir(plugin_dir, sizeof(plugin_dir), mysqld_path);
-  strcat(plugin_dir, "/" STR(INSTALL_PLUGINDIR));
+  safe_strcat(plugin_dir, sizeof(plugin_dir), "/" STR(INSTALL_PLUGINDIR));
 
   if (access(plugin_dir, 0) == 0)
     return plugin_dir;
diff --git a/sql/mysqld.cc b/sql/mysqld.cc
index e4a814b82dd..ea3849ed9f9 100644
--- a/sql/mysqld.cc
+++ b/sql/mysqld.cc
@@ -5393,12 +5393,11 @@ static int init_server_components()
     else // full wsrep initialization
     {
       // add basedir/bin to PATH to resolve wsrep script names
-      char* const tmp_path= (char*)my_alloca(strlen(mysql_home) +
-                                             strlen("/bin") + 1);
+      size_t tmp_path_size= strlen(mysql_home) + 5; /* including "/bin" */
+      char* const tmp_path= (char*)my_alloca(tmp_path_size);
       if (tmp_path)
       {
-        strcpy(tmp_path, mysql_home);
-        strcat(tmp_path, "/bin");
+        snprintf(tmp_path, tmp_path_size, "%s/bin", mysql_home);
         wsrep_prepend_PATH(tmp_path);
       }
       else
@@ -6254,8 +6253,9 @@ int mysqld_main(int argc, char **argv)
     char real_server_version[2 * SERVER_VERSION_LENGTH + 10];
 
     set_server_version(real_server_version, sizeof(real_server_version));
-    strcat(real_server_version, "' as '");
-    strcat(real_server_version, server_version);
+    safe_strcat(real_server_version, sizeof(real_server_version), "' as '");
+    safe_strcat(real_server_version, sizeof(real_server_version),
+		server_version);
 
     sql_print_information(ER_DEFAULT(ER_STARTUP), my_progname,
                           real_server_version,
@@ -9192,7 +9192,8 @@ static int mysql_init_variables(void)
     }
     else
       my_path(prg_dev, my_progname, "mysql/bin");
-    strcat(prg_dev,"/../");			// Remove 'bin' to get base dir
+    // Remove 'bin' to get base dir
+    safe_strcat(prg_dev, sizeof(prg_dev), "/../");
     cleanup_dirname(mysql_home,prg_dev);
   }
 #else