Re: [9fans] unmount

[arisawa]

I said:

> 2015/12/01 12:24、arisawa <aris...@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;
        }