Re: [RFC] [PATCH] file posix capabilities

From: Stephen Smalley
Date: Thu Aug 17 2006 - 08:24:04 EST

On Thu, 2006-08-17 at 08:00 -0400, Joshua Brindle wrote:
> Stephen Smalley wrote:
> > On Tue, 2006-08-15 at 21:42 -0500, Serge E. Hallyn wrote:
> >
> > <snip>
> >> Very good point. Preventing communication channels i.e. through signals
> >> isn't a concern, but user hallyn ptracing himself running /bin/passwd
> >> certainly is.
> >>
> >
> > Actually, ptrace already performs a capability comparison (cap_ptrace).
> > Wrt signals, it wasn't the communication channel that concerned me but
> > the ability to interfere with the operation of a process running in the
> > same uid but different capabilities, like stopping it at a critical
> > point. Likewise with many other task hooks - you wouldn't want to be
> > able to depress the priority of a process running with greater
> > capabilities.
> >
> >
> On this point, what about environment tampering of processes with caps?
> /usr/bin/passwd. glibc atsecure logic would
> have to be updated to do a capability comparison.

That's the bprm_secureexec logic change that has already been mentioned;
that determines the AT_SECURE value, and glibc then just acts based on
that value provided by the kernel. Just a matter of extending
cap_bprm_secureexec to compare the capability sets. Already on Serge's
todo list, but it is necessary for this to be a safe change, and should
happen before this patch goes anywhere (even -mm), IMHO.

Stephen Smalley
National Security Agency

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