Re: [RFC][PATCH] procfs: add privacy options

From: Arjan van de Ven
Date: Tue Jul 25 2006 - 01:50:53 EST

> You mean using ptrace_may_attach() and/or MAY_PTRACE() for determining
> access to all (or at least more) files in /proc/<pid> instead of my
> proposed "chmod 500"? What are the advantages?


file permissions are simple, but too simplistic to express a full "am I
allowed to see that guy" rules as general principle. Just think of
SELinux or any other kind of role based access control mechanism where
"root is not full root". But it goes beyond that really; applications
that drop their ptrace capability because they KNOW they won't use it
and by dropping the capability deny an exploit that takes over from
using it. There's just too many such cases that file permissions don't
capture where ptrace is a more detailed description of the permission
check you want (idea being that if you can ptrace someone you own them).
It's good general principle to at least try to not duplicate such
permission checks; history shows that those will be gotten incorrect.

Arjan van de Ven

if you want to mail me at work (you don't), use arjan (at)

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