Re: New Security Features, Please Comment

From: Geoffrey McRae
Date: Wed Dec 03 2008 - 18:41:24 EST

On Thu, 2008-12-04 at 07:27 +0800, Peter Teoh wrote:
> On Thu, Dec 4, 2008 at 7:08 AM, Alan Cox <alan@xxxxxxxxxxxxxxxxxxx> wrote:
> >> The children are pre-forked, so the overhead is in the setup... then
> >> when the app recieves a request, it sets the child's uid to the uid of
> >> the website, and then passes the request to the child, which, now, the
> >> child is running as the website owner.
> >
> > But the child process may already have been trojanned by a previous user
> > so it gains you nothing.
> >
> Yes, I thought so too. The trojanized child, even though most of the
> time unprivileged, can wait for that window of opportunity when its
> privilege is escalated, by polling, and when it received the
> privilege, immediate jump into action.
> Thanks.

Ok, so this is a pretty major flaw of the idea, thats why I put this
concept out there, any suggestions as to how to get around this?
Possibly add some checking to disable certain functions in the child
when the enable_setpresuid function has been called?.

Or save the signal handlers the first time setpresuid is called, and the
next time, restore them so if the child has changed them, they get
re-set back to their initial state?

I know many people are against the idea of adding new functions at will
to the kernel, thats why I am trying to flesh out all the potential
problems and find solutions to them first.

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