Unreadable binaries

[Adam Jackson]

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.

- ajax
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