Re: [PATCH V2] Ensure correct monolithic binary policy is loaded

[Richard Haines <richard_c_haines@btinternet.com>]

On Sat, 2020-12-19 at 15:49 -0500, Chris PeBenito wrote:
> On 12/18/20 10:03 AM, Richard Haines wrote:
> > When building a monolithic policy with 'make load', the
> > selinux_config(5) file 'SELINUXTYPE' entry determines what policy
> > is loaded as load_policy(8) does not take a path value (it always
> > loads
> > the active system policy as defined by /etc/selinux/config).
> > 
> > Currently it is possible to load the wrong binary policy, for
> > example if
> > the Reference Policy source is located at:
> > /etc/selinux/refpolicy
> > and the /etc/selinux/config file has the following entry:
> > SELINUXTYPE=targeted
> > Then the /etc/selinux/targeted/policy/policy.<ver> is loaded when
> > 'make load' is executed.
> > 
> > Another example is that if the Reference Policy source is located
> > at:
> > /tmp/custom-rootfs/etc/selinux/refpolicy
> > and the /etc/selinux/config file has the following entry:
> > SELINUXTYPE=refpolicy
> > Then the /etc/selinux/refpolicy/policy/policy.<ver> is loaded when
> > 'make DESTDIR=/tmp/custom-rootfs load' is executed (not the
> > /tmp/custom-rootfs/etc/selinux/refpolicy/policy/policy.<ver> that
> > the
> > developer thought would be loaded).
> > 
> > Resolve these issues by using selinux_path(3) to resolve the policy
> > root,
> > then checking the selinux_config(5) file for the appropriate
> > SELINUXTYPE
> > entry.
> > 
> > Remove the '@touch $(tmpdir)/load' line as the file is never
> > referenced.
> > 
> > Signed-off-by: Richard Haines <richard_c_haines@btinternet.com>
> > ---
> > V2 Changes: Use $(error .. instead of NO_LOAD logic. Use python
> > script to
> > find selinux path not sestatus. Reword error messages.
> > 
> >   Makefile                |  1 +
> >   Rules.monolithic        | 15 ++++++++++++++-
> >   support/selinux_path.py | 13 +++++++++++++
> >   3 files changed, 28 insertions(+), 1 deletion(-)
> >   create mode 100644 support/selinux_path.py
> > 
> > diff --git a/Makefile b/Makefile
> > index 6ba215f1..e49d43d0 100644
> > --- a/Makefile
> > +++ b/Makefile
> > @@ -97,6 +97,7 @@ genxml := $(PYTHON) $(support)/segenxml.py
> >   gendoc := $(PYTHON) $(support)/sedoctool.py
> >   genperm := $(PYTHON) $(support)/genclassperms.py
> >   policyvers := $(PYTHON) $(support)/policyvers.py
> > +selinux_path := $(PYTHON) $(support)/selinux_path.py
> >   fcsort := $(PYTHON) $(support)/fc_sort.py
> >   setbools := $(AWK) -f $(support)/set_bools_tuns.awk
> >   get_type_attr_decl := $(SED) -r -f
> > $(support)/get_type_attr_decl.sed
> > diff --git a/Rules.monolithic b/Rules.monolithic
> > index a8ae98d1..cd065362 100644
> > --- a/Rules.monolithic
> > +++ b/Rules.monolithic
> > @@ -42,6 +42,12 @@ vpath %.te $(all_layers)
> >   vpath %.if $(all_layers)
> >   vpath %.fc $(all_layers)
> >   
> > +# load_policy(8) loads policy from
> > <SELINUX_PATH>/<SELINUXTYPE>/policy/policy.<ver>
> > +# It does this by reading the <SELINUX_PATH>/config file and using
> > the
> > +# SELINUX_PATH/SELINUXTYPE entries to form the initial path.
> > +SELINUX_PATH := $(shell $(selinux_path))
> > +SELINUXTYPE := $(strip $(shell $(AWK) -F= '/^SELINUXTYPE/{ print
> > $$2 }' $(SELINUX_PATH)/config))
> > +
> >   ########################################
> >   #
> >   # default action: build policy locally
> > @@ -91,9 +97,16 @@ endif
> >   # Load the binary policy
> >   #
> >   reload $(tmpdir)/load: $(loadpath) $(fcpath) $(appfiles)
> > +ifneq ($(SELINUXTYPE),$(NAME))
> > +       $(error Cannot load policy as $(SELINUX_PATH)/config file
> > contains SELINUXTYPE=$(SELINUXTYPE) - \
> > +               Edit $(SELINUX_PATH)/config and set
> > "SELINUXTYPE=$(NAME)")
> > +endif
> > +ifneq ($(topdir),$(SELINUX_PATH))
> > +       $(error Cannot load policy as policy root MUST be
> > $(SELINUX_PATH)/$(NAME) - \
> > +               Current policy root is: $(topdir)/$(NAME))
> > +endif
> >         @echo "Loading $(NAME) $(loadpath)"
> >         $(verbose) $(LOADPOLICY) -q $(loadpath)
> > -       @touch $(tmpdir)/load
> >   
> >   ########################################
> >   #
> > diff --git a/support/selinux_path.py b/support/selinux_path.py
> > new file mode 100644
> > index 00000000..b663ff09
> > --- /dev/null
> > +++ b/support/selinux_path.py
> > @@ -0,0 +1,13 @@
> > +#!/usr/bin/env python3
> > +
> > +try:
> > +    import warnings
> > +    with warnings.catch_warnings():
> > +        warnings.filterwarnings("ignore",
> > category=PendingDeprecationWarning)
> > +        import selinux
> > +
> > +    if selinux.is_selinux_enabled():
> > +        # Strip the trailing '/'
> > +        print(selinux.selinux_path()[:-1])
> 
> Why not use selinux.selinux_binary_policy_path()? Then you don't need
> to parse 
> for SELINUXTYPE above.

Because it has more information than needed. How about using
selinux.selinux_policy_root() to give:

# load_policy(8) loads policy from <POLICY_ROOT>/policy/policy.<ver>
# It does this by reading the <SELINUX_PATH>/config file and using the
# SELINUX_PATH/SELINUXTYPE entry to form the <POLICY_ROOT>.
POLICY_ROOT := $(shell $(selinux_policy_root))
SELINUXTYPE := $(shell basename $(POLICY_ROOT))
SELINUX_PATH := $(shell dirname $(POLICY_ROOT))


> 
>