Re: [PATCH net-next v5 1/3] scm: add SO_PASSPIDFD and SCM_PIDFD

[Simon Horman <simon.horman@corigine.com>]

On Mon, May 22, 2023 at 11:47:08AM +0200, Christian Brauner wrote:
> On Sat, May 20, 2023 at 10:11:36PM +0800, kernel test robot wrote:
> > Hi Alexander,
> > 
> > kernel test robot noticed the following build errors:
> > 
> > [auto build test ERROR on net-next/main]
> > 
> > url:    https://github.com/intel-lab-lkp/linux/commits/Alexander-Mikhalitsyn/scm-add-SO_PASSPIDFD-and-SCM_PIDFD/20230517-193620
> > base:   net-next/main
> > patch link:    https://lore.kernel.org/r/20230517113351.308771-2-aleksandr.mikhalitsyn%40canonical.com
> > patch subject: [PATCH net-next v5 1/3] scm: add SO_PASSPIDFD and SCM_PIDFD
> > config: powerpc-randconfig-s043-20230517
> > compiler: powerpc-linux-gcc (GCC) 12.1.0
> > reproduce:
> >         wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
> >         chmod +x ~/bin/make.cross
> >         # apt-get install sparse
> >         # sparse version: v0.6.4-39-gce1a6720-dirty
> >         # https://github.com/intel-lab-lkp/linux/commit/969a57c99c9d50bfebd0908f5157870b36c271c7
> >         git remote add linux-review https://github.com/intel-lab-lkp/linux
> >         git fetch --no-tags linux-review Alexander-Mikhalitsyn/scm-add-SO_PASSPIDFD-and-SCM_PIDFD/20230517-193620
> >         git checkout 969a57c99c9d50bfebd0908f5157870b36c271c7
> >         # save the config file
> >         mkdir build_dir && cp config build_dir/.config
> >         COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-12.1.0 make.cross C=1 CF='-fdiagnostic-prefix -D__CHECK_ENDIAN__' O=build_dir ARCH=powerpc olddefconfig
> >         COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-12.1.0 make.cross C=1 CF='-fdiagnostic-prefix -D__CHECK_ENDIAN__' O=build_dir ARCH=powerpc SHELL=/bin/bash
> > 
> > If you fix the issue, kindly add following tag where applicable
> > | Reported-by: kernel test robot <lkp@intel.com>
> > | Closes: https://lore.kernel.org/oe-kbuild-all/202305202107.BQoPnLYP-lkp@intel.com/
> > 
> > All errors (new ones prefixed by >>, old ones prefixed by <<):
> > 
> > >> ERROR: modpost: "pidfd_prepare" [net/unix/unix.ko] undefined!
> 
> TLI, that AF_UNIX can be a kernel module...
> I'm really not excited in exposing pidfd_prepare() to non-core kernel
> code. Would it be possible to please simply refuse SO_PEERPIDFD and
> SCM_PIDFD if AF_UNIX is compiled as a module? I feel that this must be
> super rare because it risks breaking even simplistic userspace.

It occurs to me that it may be simpler to not allow AF_UNIX to be a module.
But perhaps that breaks something for someone...