Re: [PATCH] fedora: Replace pasta hard links by copies, mangle Build-IDs

["Richard W.M. Jones" <rjones@redhat.com>]

On Wed, Aug 23, 2023 at 03:59:39PM +0200, Stefano Brivio wrote:
> On Wed, 23 Aug 2023 14:53:27 +0100
> "Richard W.M. Jones" <rjones@redhat.com> wrote:
> 
> > On Wed, Aug 23, 2023 at 03:48:44PM +0200, Stefano Brivio wrote:
> > > The hard link trick didn't actually fix the issue with SELinux file
> > > contexts properly: as opposed to symbolic links, SELinux now
> > > correctly associates types to the labels that are set -- except that
> > > those labels are now shared, so we can end up (depending on how
> > > rpm(8) extracts the archives) with /usr/bin/passt having a
> > > pasta_exec_t context.
> > > 
> > > This got rather confusing as running restorecon(8) seemed to fix up
> > > labels -- but that's simply toggling between passt_exec_t and
> > > pasta_exec_t for both links, because each invocation will just "fix"
> > > the file with the mismatching context.
> > > 
> > > Replace the hard links with copies. AppArmor's attachment, instead,
> > > works with hard links, and if there's no LSM, we can keep symbolic
> > > links, so keep symbolic links in the Makefile.
> > > 
> > > With copies, rpmbuild(8) will warn about duplicate Build-IDs in the
> > > same package. Mangle them in pasta binaries by summing one to the
> > > last byte, modulo one byte, using xxd (provided by vim-common) and
> > > disable the automatic rehashing by find-debuginfo(1) -- we already
> > > have per-release Build-IDs thanks to $VERSION passed on 'make'.  
> > 
> > Right, this ^ was going to be my comment.  RPM doesn't like having two
> > identical copies of a file.
> 
> In which other way, though? cpio(1) is fine with it, and I tried to
> install the package on both ext4 and xfs -- the only warning I got was
> the (semi-reasonable) one from rpmbuild about duplicate Build-IDs.

I'm fairly sure I've seen an error when you have two identical files;
it might only happen in Koji.  Anyway, hacking the binary is surely
wrong, but let's hear the opinions of the Fedora / SELinux developers.

Rich.

> > Hacking the binary to "fix" the problem doesn't sound like a solution.
> > 
> > I'm CC-ing Fedora-devel-list to find out we can properly fix this issue.
> > 
> > Rich.
> > 
> > > Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
> > > ---
> > >  contrib/fedora/passt.spec | 27 ++++++++++++++++++++++-----
> > >  1 file changed, 22 insertions(+), 5 deletions(-)
> > > 
> > > diff --git a/contrib/fedora/passt.spec b/contrib/fedora/passt.spec
> > > index d0c6895..51bf5a8 100644
> > > --- a/contrib/fedora/passt.spec
> > > +++ b/contrib/fedora/passt.spec
> > > @@ -9,6 +9,10 @@
> > >  
> > >  %global git_hash {{{ git_head }}}
> > >  %global selinuxtype targeted
> > > +# Different Build-IDs for passt and pasta: don't let find-debuginfo touch them
> > > +%undefine _unique_build_ids
> > > +%global _no_recompute_build_ids 1
> > > +
> > >  
> > >  Name:		passt
> > >  Version:	{{{ git_version }}}
> > > @@ -19,7 +23,7 @@ Group:		System Environment/Daemons
> > >  URL:		https://passt.top/
> > >  Source:		https://passt.top/passt/snapshot/passt-%{git_hash}.tar.xz
> > >  
> > > -BuildRequires:	gcc, make, checkpolicy, selinux-policy-devel
> > > +BuildRequires:	gcc, make, checkpolicy, selinux-policy-devel, binutils, vim-common
> > >  Requires:	(%{name}-selinux = %{version}-%{release} if selinux-policy-%{selinuxtype})
> > >  
> > >  %description
> > > @@ -56,15 +60,28 @@ This package adds SELinux enforcement to passt(1) and pasta(1).
> > >  %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
> > > +# The Makefile creates symbolic links for pasta, but we need actual copies for
> > >  # SELinux file contexts to work as intended. Same with pasta.avx2 if present.
> > > -ln -f %{buildroot}%{_bindir}/passt %{buildroot}%{_bindir}/pasta
> > > +#
> > > +# To avoid duplicate Build-IDs in the same package, we increase the last byte of
> > > +# the value for pasta binaries by one (modulo one byte). Note that we already
> > > +# have differentiated Build-IDs per release, courtesy of $VERSION, so we don't
> > > +# need find-debuginfo(1) to recalculate them.
> > > +rm %{buildroot}%{_bindir}/pasta
> > > +objcopy --dump-section .note.gnu.build-id=%{buildroot}/build_id %{buildroot}%{_bindir}/passt
> > > +printf '\x'$(printf %02x $(( ( 0x$(xxd -ps -s 35 %{buildroot}/build_id) + 1 ) % 0xff )) ) | dd of=%{buildroot}/build_id seek=35 bs=1 count=1 conv=notrunc
> > > +objcopy --update-section .note.gnu.build-id=%{buildroot}/build_id %{buildroot}%{_bindir}/passt %{buildroot}%{_bindir}/pasta
> > > +rm %{buildroot}/build_id
> > > +
> > >  %ifarch x86_64
> > > -ln -f %{buildroot}%{_bindir}/passt.avx2 %{buildroot}%{_bindir}/pasta.avx2
> > > +rm %{buildroot}%{_bindir}/pasta.avx2
> > > +objcopy --dump-section .note.gnu.build-id=%{buildroot}/build_id %{buildroot}%{_bindir}/passt.avx2
> > > +printf '\x'$(printf %02x $(( ( 0x$(xxd -ps -s 35 %{buildroot}/build_id) + 1 ) % 0xff )) ) | dd of=%{buildroot}/build_id seek=35 bs=1 count=1 conv=notrunc
> > > +objcopy --update-section .note.gnu.build-id=%{buildroot}/build_id %{buildroot}%{_bindir}/passt.avx2 %{buildroot}%{_bindir}/pasta.avx2
> > > +rm %{buildroot}/build_id
> > >  
> > >  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
> > >  
> > >  pushd contrib/selinux
> > > -- 
> > > 2.39.2  
> 
> -- 
> Stefano

-- 
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
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