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

[Stefano Brivio <sbrivio@redhat.com>]

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.

> 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