Re: [PATCH v2 1/7] fedora: Install pasta as hard link to ensure SELinux file context match

On Thu, 17 Aug 2023 08:53:55 +0100
"Richard W.M. Jones" <rjones(a)redhat.com> wrote:

...
  On Wed, Aug 16, 2023 at 08:17:24PM +0200, Stefano
Brivio wrote:
  The Makefile installs symbolic links by default,
which actually
 worked at some point (not by design) with SELinux, but at least on
 recent kernel versions it doesn't anymore: override pasta (and
 pasta.avx2) with hard links.
 
 Otherwise, even if the links are labeled as pasta_exec_t, SELinux
 will "resolve" them to passt_exec_t, and we'll have pasta running as
 passt_t instead of pasta_t.
 
 Signed-off-by: Stefano Brivio <sbrivio(a)redhat.com>
 ---
  contrib/fedora/passt.spec | 7 +++++++
  1 file changed, 7 insertions(+)
 
 diff --git a/contrib/fedora/passt.spec b/contrib/fedora/passt.spec
 index 8d28ef6..d0c6895 100644
 --- a/contrib/fedora/passt.spec
 +++ b/contrib/fedora/passt.spec
 @@ -54,10 +54,17 @@ This package adds SELinux enforcement to passt(1) and pasta(1).
  %make_build VERSION="%{version}-%{release}.%{_arch}"
  
  %install
 +
  %make_install DESTDIR=%{buildroot} prefix=%{_prefix} bindir=%{_bindir} mandir=%{_mandir}
docdir=%{_docdir}/%{name}
 +# The Makefile creates symbolic links for pasta, but we need hard links for
 +# SELinux file contexts to work as intended. Same with pasta.avx2 if present.
 +ln -f %{buildroot}%{_bindir}/passt %{buildroot}%{_bindir}/pasta
  %ifarch x86_64
 +ln -f %{buildroot}%{_bindir}/passt.avx2 %{buildroot}%{_bindir}/pasta.avx2
 +
  ln -sr %{buildroot}%{_mandir}/man1/passt.1 %{buildroot}%{_mandir}/man1/passt.avx2.1
  ln -sr %{buildroot}%{_mandir}/man1/pasta.1 %{buildroot}%{_mandir}/man1/pasta.avx2.1
 +install -p -m 755 %{buildroot}%{_bindir}/passt.avx2 %{buildroot}%{_bindir}/pasta.avx2
  %endif   
 
 Acked-by: Richard W.M. Jones <rjones(a)redhat.com>
 
 ... although why not change the Makefile install rule instead so
 everyone gets this change? 
Because that's only needed for SELinux "based" distributions. I have
the feeling that symlinks are in general more desirable -- at least
personally I find them less confusing.

Also, David pointed out that hard links are not supported by a number
of filesystems, and we probably don't want to mess this up for
embedded environments.

On the other hand, I didn't check yet if AppArmor would also benefit
from this -- there we have at the moment a single profile for passt and
pasta (the symlink behaviour is documented)... if it does, I guess it
might make sense to switch to hard links in the Makefile (assuming
there are no issues with other distributions), and perhaps export a
Makefile variable to have symlinks instead.

-- 
Stefano