Re: [uml-devel] T-mode processes

[BlaisorBlade <blaisorblade_spam@yahoo.it>]

On Sunday 03 October 2004 19:44, Michael Richardson wrote:
> >>>>> "BlaisorBlade" == BlaisorBlade  <blaisorblade_spam@yahoo.it> writes:
>     >> We also continue to have an issue with the /proc/PID/environ file
>     >> not being owned by the process involved.
>
>     BlaisorBlade> I'm looking at the permission in your listing and in
>     BlaisorBlade> my linux, and I don't see anything strange. Plus, I
>     BlaisorBlade> don't understand what you mean with "a file owned by a
>     BlaisorBlade> certain process".
>
>     BlaisorBlade> Do you mean "I start the process with uid build and
>     BlaisorBlade> /proc/PID/* has uid root while it should have uid
>     BlaisorBlade> build"?
>
>   Yes.
>
>     BlaisorBlade> If you mean this, the answer is that you seem to be
>     BlaisorBlade> starting UML with one id and making it run with
>     BlaisorBlade> another UID. At least, I see this permission situation
>     BlaisorBlade> with the X Font Server:

>   No, this is not the case.
>   It runs as "build" and that is all.

>   The problem is that the use of mm confuses the proc-permission system
> into thinking that the process is setuid. I wandered through this last
> year, when we first noticed this problem.

>   This seems to be due to how mm->dumpable is initalized.
> (see task_dumpable in fs/proc/base.c)
>   I tried to change it, but I was not successful. I can dig up my
> attempts, but they are on the list.

Oh, ok... this can be fixed, I guess, with these infos... I'll come back to 
this when I have time.

Actually, what I should do is to set the "mm->dumpable" flag to 1 inside 
mm/proc_mm.c (after mm_alloc(), it is 0). The situation is clear. However, to 
write a good patch, I want to study well the "mm->dumpable" flag use (when 
it's set, when not...) otherwise I could open a security hole (even because 
there are people using UML setuid to root, for the mlock() patch).

Bye
-- 
Paolo Giarrusso, aka Blaisorblade
Linux registered user n. 292729


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