Added a new function SetFilePermissions to set permissions of a file. I'm not sure about the Windows implementation. See this feature request: https://bugs.alliedmods.net/show_bug.cgi?id=6152

core/logic/smn_filesystem.cpp

@@ -39,6 +39,11 @@
 #include <ITranslator.h>
 #include "common_logic.h"
 
+#if defined PLATFORM_WINDOWS
+#include <io.h>
+#include "smn_filesystem.h"
+#endif
+
 HandleType_t g_FileType;
 HandleType_t g_DirType;
 IChangeableForward *g_pLogHook = NULL;
@@ -465,6 +470,31 @@ static cell_t sm_FileSize(IPluginContext *pContext, const cell_t *params)
 #endif
 }
 
+static cell_t sm_SetFilePermissions(IPluginContext *pContext, const cell_t *params)
+{
+	char *name;
+	char realpath[PLATFORM_MAX_PATH];
+
+	pContext->LocalToString(params[1], &name);
+	g_pSM->BuildPath(Path_Game, realpath, sizeof(realpath), "%s", name);
+
+#if defined PLATFORM_WINDOWS
+	int mask;
+	if (params[2] & FPERM_U_WRITE || params[2] & FPERM_G_WRITE || params[2] & FPERM_O_WRITE)
+	{
+		mask |= _S_IWRITE;
+	}
+	if (params[2] & FPERM_U_READ || params[2] & FPERM_G_READ || params[2] & FPERM_O_READ ||
+		params[2] & FPERM_U_EXEC || params[2] & FPERM_G_EXEC || params[2] & FPERM_O_EXEC)
+	{
+		mask |= _S_IREAD;
+	}
+	return _chmod(realpath, mask) == 0;
+#else
+	return chmod(realpath, params[2]) == 0;
+#endif
+}
+
 static cell_t sm_CreateDirectory(IPluginContext *pContext, const cell_t *params)
 {
 	char *name;
@@ -971,5 +1001,6 @@ REGISTER_NATIVES(filesystem)
 	{"AddGameLogHook",			sm_AddGameLogHook},
 	{"RemoveGameLogHook",		sm_RemoveGameLogHook},
 	{"CreateDirectory",			sm_CreateDirectory},
+	{"SetFilePermissions",		sm_SetFilePermissions},
 	{NULL,						NULL},
 };

core/logic/smn_filesystem.h

@@ -0,0 +1,45 @@
+/**
+ * vim: set ts=4 :
+ * =============================================================================
+ * SourceMod
+ * Copyright (C) 2004-2008 AlliedModders LLC.  All rights reserved.
+ * =============================================================================
+ *
+ * This program is free software; you can redistribute it and/or modify it under
+ * the terms of the GNU General Public License, version 3.0, as published by the
+ * Free Software Foundation.
+ * 
+ * This program is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
+ * FOR A PARTICULAR PURPOSE.  See the GNU General Public License for more
+ * details.
+ *
+ * You should have received a copy of the GNU General Public License along with
+ * this program.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ * As a special exception, AlliedModders LLC gives you permission to link the
+ * code of this program (as well as its derivative works) to "Half-Life 2," the
+ * "Source Engine," the "SourcePawn JIT," and any Game MODs that run on software
+ * by the Valve Corporation.  You must obey the GNU General Public License in
+ * all respects for all other code used.  Additionally, AlliedModders LLC grants
+ * this exception to all derivative works.  AlliedModders LLC defines further
+ * exceptions, found in LICENSE.txt (as of this writing, version JULY-31-2007),
+ * or <http://www.sourcemod.net/license.php>.
+ *
+ * Version: $Id$
+ */
+
+#ifndef _INCLUDE_SOURCEMOD_FILESYSTEM_H_
+#define _INCLUDE_SOURCEMOD_FILESYSTEM_H_
+
+#define FPERM_U_READ		0x0100	/* User can read. */
+#define FPERM_U_WRITE		0x0080	/* User can write. */
+#define FPERM_U_EXEC		0x0040	/* User can exec. */
+#define FPERM_G_READ		0x0020	/* Group can read. */
+#define FPERM_G_WRITE		0x0010	/* Group can write. */
+#define FPERM_G_EXEC		0x0008	/* Group can exec. */
+#define FPERM_O_READ		0x0004	/* Anyone can read. */
+#define FPERM_O_WRITE		0x0002	/* Anyone can write. */
+#define FPERM_O_EXEC		0x0001	/* Anyone can exec. */
+
+#endif //_INCLUDE_SOURCEMOD_FILESYSTEM_H_

plugins/include/files.inc

@@ -376,6 +376,15 @@ native bool:RemoveDir(const String:path[]);
  */
 native bool:CreateDirectory(const String:path[], mode);
 
+/**
+ * Changes a file or directories permissions.
+ *
+ * @param path			Path to the file.
+ * @param mode			Permissions to set.
+ * @return				True on success, false otherwise.
+ */
+native bool:SetFilePermissions(const String:path[], mode);
+
 /**
  * Returns a file timestamp as a unix timestamp.
  *