Re: [9fans] unmount

[arisawa <arisawa@ar.aichi-u.ac.jp>]

I said:

> 2015/12/01 12:24、arisawa <arisawa@ar.aichi-u.ac.jp> のメール：
> 
> Hello 9fans,
> 
> current kernel allows unmount even if after rfork m.
> this feature makes sandboxing difficult.
> can anyone explain this feature is necessary?
> 
> Kenji Arisawa

I make a protection for unmounting after rfork -m and now testing.
my idea is: protecting unmount with a single argument.
it seems the following code is working, however I am not sure this is OK.
any comment welcome.

/sys/src/9/port/sysfile.c:

sysunmount(va_list list)
{
	Chan *cmount, *cmounted;
	char *name, *old;

	name = va_arg(list, char*);
	old = va_arg(list, char*);

	/*	a protection for 'unmount' after 'rfork m'
	*	we can reject any unmount, however it might not be user friendly to do so.
	*	more moderate way might be disallowing
	*		unmount mntpoint	# sigle argument
	*	it is ideal though: we disalow unmount dirs that are mounted before rfork m.
	*	probably we need this protection also in regular kernel
	*
	*	print("name=%s old=%s\n",name,old);
	*	the output is, e.g,
	*	name=srv/factorum
	*	old=/mnt
	*	-Kenar-	*/

	if(up->pgrp->noattach && (name == nil)){
		error(Eperm);
		return 0;
	}