[REVIEW][PATCH 1/2] vfs: Commit to never having exectuables on proc and sysfs.

Greg Kroah-Hartman gregkh at linuxfoundation.org
Fri Jul 10 19:30:52 UTC 2015

On Fri, Jul 10, 2015 at 08:24:41PM +0200, Richard Weinberger wrote:
> Am 10.07.2015 um 18:17 schrieb Eric W. Biederman:
> > 
> > Today proc and sysfs do not contain any executable files.  Several
> > applications today mount proc or sysfs without noexec and nosuid and
> > then depend on there being no exectuables files on proc or sysfs.
> > Having any executable files show on proc or sysfs would cause
> > a user space visible regression, and most likely security problems.
> > 
> > Therefore commit to never allowing executables on proc and sysfs by
> > adding a new flag to mark them as filesystems without executables and
> > enforce that flag.
> > 
> > Test the flag where MNT_NOEXEC is tested today, so that the only user
> > visible effect will be that exectuables will be treated as if the
> > execute bit is cleared.
> > 
> > The filesystems proc and sysfs do not currently incoporate any
> > executable files so this does not result in any user visible effects.
> > 
> > This makes it unnecessary to vet changes to proc and sysfs tightly for
> > adding exectuable files or changes to chattr that would modify
> > existing files, as no matter what the individual file say they will
> > not be treated as exectuable files by the vfs.
> > 
> > Not having to vet changes to closely is important as without this we
> > are only one proc_create call (or another goof up in the
> > implementation of notify_change) from having problematic executables
> > on proc.  Those mistakes are all too easy to make and would create
> > a situation where there are security issues or the assumptions of
> > some program having to be broken (and cause userspace regressions).
> Would it make sense to add SB_I_NOEXEC to more pseudo filesystems?
> Say pstore or devpts?

And configfs and cgroupfs?

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