Re: [RFC] [PATCH] file posix capabilities

[Joshua Brindle <method@gentoo.org>]

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? 
LD_PRELOAD=my_bad_lib.so /usr/bin/passwd. glibc atsecure logic would 
have to be updated to do a capability comparison.

> One other point to consider is Solaris seems to have diverged from their
> own past approaches for privileges/capabilities,
> http://blogs.sun.com/casper/20040722
> http://www.opensolaris.org/os/community/security/library/howto/privbracket/
>
> Doesn't sound like they are even using file capabilities at all.
>
> Also, think about the real benefits of capabilities, at least as defined
> in Linux.  The coarse granularity and the lack of any per-object support
> is a fairly significant deficiency there that is much better handled via
> TE.  At least some of the Linux capabilities lend themselves to easy
> privilege escalation to gaining other capabilities or effectively
> bypassing them