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

On 12/17/20 11:42 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/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/refpolicy/policy/policy.<ver> that the developer
> thought would be loaded).
> 
> Resolve these issues by using sestatus(8) 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 <[email protected]>
> ---
>   Makefile         |  1 +
>   Rules.monolithic | 31 ++++++++++++++++++++++++++++---
>   2 files changed, 29 insertions(+), 3 deletions(-)
> 
> diff --git a/Makefile b/Makefile
> index 6ba215f1..88a5e78f 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -64,6 +64,7 @@ SEMOD_EXP ?= $(tc_usrbindir)/semodule_expand
>   LOADPOLICY ?= $(tc_usrsbindir)/load_policy
>   SEPOLGEN_IFGEN ?= $(tc_usrbindir)/sepolgen-ifgen
>   SETFILES ?= $(tc_sbindir)/setfiles
> +SESTATUS ?= $(tc_sbindir)/sestatus
>   XMLLINT ?= $(BINDIR)/xmllint
>   SECHECK ?= $(BINDIR)/sechecker
>   
> diff --git a/Rules.monolithic b/Rules.monolithic
> index a8ae98d1..01e445ca 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 <SELINUXDIR>/<SELINUXTYPE>/policy/policy.<ver>
> +# Therefore need to determine if policy to load is in the right place,
> +SELINUXDIR ?= $(strip $(shell $(SESTATUS) | $(AWK) '/^SELinux root directory:/{ print $$4 }'))
> +# and that <SELINUXDIR>/config contains the correct SELINUXTYPE entry.
> +SELINUXTYPE ?= $(strip $(shell $(AWK) -F= '/^SELINUXTYPE/{ print $$2 }' $(SELINUXDIR)/config))

Rather than parsing sestatus output, I'd prefer do a tiny Python script that 
gets the policy path, e.g.:

python -c 'import selinux; print(selinux.selinux_binary_policy_path())'

See support/policyvers.py too.

>   ########################################
>   #
>   # default action: build policy locally
> @@ -91,9 +97,28 @@ endif
>   # Load the binary policy
>   #
>   reload $(tmpdir)/load: $(loadpath) $(fcpath) $(appfiles)
> -	@echo "Loading $(NAME) $(loadpath)"
> -	$(verbose) $(LOADPOLICY) -q $(loadpath)
> -	@touch $(tmpdir)/load
> +ifneq ($(SELINUXTYPE),$(NAME))
> +	$(eval NO_LOAD := $(shell echo 1))

I think it would be cleaner to use the $(error msg_text) function to terminate 
make rather than the NO_LOAD logic.

See https://www.gnu.org/software/make/manual/make.html#Make-Control-Functions

> +	@echo
> +	@echo "Warning: Cannot load policy as $(SELINUXDIR)/config file contains:"
> +	@echo -e "\tSELINUXTYPE=$(SELINUXTYPE)"
> +	@echo "Edit $(SELINUXDIR)/config and set \"SELINUXTYPE=$(NAME)\"."
> +	@echo
> +endif
> +
> +ifneq ($(topdir),$(SELINUXDIR))
> +	$(eval NO_LOAD := $(shell echo 1))
> +	@echo
> +	@echo "Warning: Cannot load policy as policy root MUST be $(SELINUXDIR)/$(NAME)"
> +	@echo
> +endif
> +
> +	@if test -z $(NO_LOAD); then \
> +		echo "Loading $(NAME) $(loadpath)" ;\
> +		$(verbose) $(LOADPOLICY) -q $(loadpath) ;\
> +	else \
> +		echo "Resolve binary policy configuration" ;\
> +	fi
>   
>   ########################################
>   #
> 


-- 
Chris PeBenito