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

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 <[email protected]>
> ---
> 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.


-- 
Chris PeBenito