Re: RFC: disablenetwork facility. (v4)

[Bryan Donlan]

On Tue, Dec 29, 2009 at 11:39 AM, Serge E. Hallyn <serue@xxxxxxxxxx> wrote:
> Quoting Bryan Donlan (bdonlan@xxxxxxxxx):
>> On Tue, Dec 29, 2009 at 10:11 AM, Serge E. Hallyn <serue@xxxxxxxxxx> wrote:
>> > Eric, let me specifically point out a 'disable setuid-root'
>> > problem on linux: root still owns most of the system even when
>> > it's not privileged.  So does "disable setuid-root" mean
>> > we don't allow exec of setuid-root binaries at all, or that
>> > we don't setuid to root, or that we just don't raise privileges
>> > for setuid-root?
>>
>> I, for one, think it would be best to handle it exactly like the
>> nosuid mount option - that is, pretend the file doesn't have any
>> setuid bits set. There's no reason to deny execution; if the process
>> would otherwise be able to execute it, it can also copy the file to
>> make a non-suid version and execute that instead. And some programs
>> can operate with reduced function without setuid. For example, screen
>> comes to mind; it needs root to share screen sessions between multiple
>> users, but can operate for a single user just fine without root, and
>> indeed the latter is usually the default configuration.
>
> That's fine with me, seems safe for a fully unprivileged program to
> use, and would make sense to do through one of the securebits set
> with prctl(PR_SET_SECUREBITS).
>
> In addition, I assume we would also refuse to honor file capabilities?

Yes - essentially a one-time switch saying "never allow me to gain
capabilities again".
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