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

[Chris PeBenito <pebenito@ieee.org>]

On 12/20/20 7:31 AM, Richard Haines wrote:
> 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))

On second thought, isn't another way of doing the check:

selinux.selinux_binary_policy_path() + "." + POLICYVER == $(loadpath)?



-- 
Chris PeBenito