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Re: Unreadable binaries



On Thu, Oct 22, 2009 at 09:59:00AM -0400, Stephen Smalley wrote:
> On Thu, 2009-10-22 at 09:48 -0400, Adam Jackson wrote:
> > On Thu, 2009-10-22 at 11:04 +0100, Richard W.M. Jones wrote:
> > > $ ll /usr/libexec/pt_chown 
> > > -rws--x--x 1 root root 28418 2009-09-28 13:42 /usr/libexec/pt_chown
> > > $ ll /usr/bin/chsh 
> > > -rws--x--x 1 root root 18072 2009-10-05 16:28 /usr/bin/chsh
> > > 
> > > What is the purpose of making binaries like these unreadable?
> > > 
> > > Originally I thought it was something to do with them being setuid,
> > > but there are counterexamples:
> > > 
> > > $ ll /usr/bin/passwd 
> > > -rwsr-xr-x 1 root root 25336 2009-09-14 13:14 /usr/bin/passwd
> > 
> > Historically, the kernel considers read permission on a binary to be a
> > prerequisite for generating core dumps on fatal signal; which you
> > typically want to prevent, since that becomes a way to read /etc/shadow.
> > 
> > Pretty sure that's still the case, which means any u+s binaries with
> > group/other read permission are bugs.
> 
> dumpable flag gets cleared for suid/sgid binaries (as well as for
> non-readable binaries).

Stephen, what would be your advice if I asked for these binaries to
become readable by non-root users?

[It's not crucial at the moment, however, just reduces the
effectiveness of febootstrap a little]

Rich.

-- 
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
libguestfs lets you edit virtual machines.  Supports shell scripting,
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