Re: [RFC][PATCH] Unprivileged: Disable acquisition of privileges

[Bryan Donlan]

On Tue, Dec 29, 2009 at 11:33 PM, Eric W. Biederman
<ebiederm@xxxxxxxxxxxx> wrote:
> Bryan Donlan <bdonlan@xxxxxxxxx> writes:
>
>> Is this sufficient for other security models such as selinux or
>> TOMOYO? Can processes in these models gain privileges through means
>> not restricted here?
>
> The LSM is primarily about returning -EPERM more often.
> Except for the prctl and the capability hooks I am not aware
> of anywhere a LSM can increase a processes capabilities.

I'm more concerned about a case where a privilege that the LSM
currently denies is lifted by execing some executable - this is still
an increase in privilege, even though the LSM only adds additional
restrictions. That is:

1) Initial state: LSM denies access to /somefile (although normal
POSIX permissions would permit access)
2) Disable capability-gaining
3) Disable network access with proposed API
4) Exec some application, which is labeled in a way that permits
access to /somefile
5) Application fails to access the network, then does something to /somefile

I'm not entirely sure if step 4) can happen in any of the currently
existing LSMs - if it's not possible to gain privileges in them via a
suid-like mechanism, this isn't a problem, but it's something that
needs to be checked for.
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