SaveActions: Set file permissions of backup copies to 0600

As discussed in SF bug #125, it might be dangerous to store backup
copies in a publicly accessable directory like /tmp with default
permissions, especially on multi-user systems.
So set the file permissions on non-Windows systems to 0600 by default.
Also improve the documentation of the save Actions plugin to reflect this
change.

doc/geany.txt

@@ -5176,8 +5176,23 @@ you can configure the automatically added extension in the configure dialog
 in Geany's plugin manager.
 
 After the plugin was loaded in Geany's plugin manager, every file is
-copied into the configured backup directory when the file is saved in Geany.
-
+copied into the configured backup directory *after* the file has been saved
+in Geany.
+
+The created backup copy file permissions are set to read-write only for
+the user. This should help to not create world-readable files on possibly
+unsecure destination directories like /tmp (especially useful
+on multi-user systems).
+This applies only to non-Windows systems. On Windows, no explicit file
+permissions are set.
+
+
+Additionally, you can define how many levels of the original file's
+directory structure should be replicated in the backup copy path.
+For example, setting the option
+*Directory levels to include in the backup destination* to *2*
+cause the plugin to create the last two components of the original
+file's path in the backup copy path and place the new file there.
 
 
 Contributing to this document

plugins/saveactions.c

@@ -27,6 +27,8 @@
 #include "geanyplugin.h"
 #include "gtkcompat.h"
 
+#include <stdio.h>
+#include <fcntl.h>
 #include <unistd.h>
 #include <errno.h>
 #include <glib/gstdio.h>
@@ -195,6 +197,7 @@ static void backupcopy_document_save_cb(GObject *obj, GeanyDocument *doc, gpoint
 	gchar *dir_parts_src;
 	gchar *stamp;
 	gchar buf[512];
+	gint fd_dst = -1;
 
 	if (! enable_backupcopy)
 		return;
@@ -220,14 +223,23 @@ static void backupcopy_document_save_cb(GObject *obj, GeanyDocument *doc, gpoint
 	g_free(basename_src);
 	g_free(dir_parts_src);
 
+#ifdef G_OS_WIN32
 	if ((dst = g_fopen(locale_filename_dst, "wb")) == NULL)
+#else
+	/* Use g_open() on non-Windows to set file permissions to 600 atomically.
+	 * On Windows, seting file permissions would require specific Windows API. */
+	fd_dst = g_open(locale_filename_dst, O_CREAT | O_WRONLY, S_IWUSR | S_IRUSR);
+	if (fd_dst == -1 || (dst = fdopen(fd_dst, "w")) == NULL)
+#endif
 	{
 		ui_set_statusbar(FALSE, _("Backup Copy: File could not be saved (%s)."),
 			g_strerror(errno));
 		g_free(locale_filename_src);
 		g_free(locale_filename_dst);
 		g_free(stamp);
 		fclose(src);
+		if (fd_dst != -1)
+			close(fd_dst);
 		return;
 	}
 
@@ -238,6 +250,8 @@ static void backupcopy_document_save_cb(GObject *obj, GeanyDocument *doc, gpoint
 
 	fclose(src);
 	fclose(dst);
+	if (fd_dst != -1)
+		close(fd_dst);
 	g_free(locale_filename_src);
 	g_free(locale_filename_dst);
 	g_free(stamp);