Re: [PATCH v2 09/11] ima: Move validation of the keyrings conditional into ima_validate_rule()

[Mimi Zohar]

On Thu, 2020-07-02 at 17:16 -0500, Tyler Hicks wrote:
> On 2020-06-30 19:07:29, Mimi Zohar wrote:
> > On Fri, 2020-06-26 at 17:38 -0500, Tyler Hicks wrote:
> > > Use ima_validate_rule() to ensure that the combination of a hook
> > > function and the keyrings conditional is valid and that the keyrings
> > > conditional is not specified without an explicit KEY_CHECK func
> > > conditional. This is a code cleanup and has no user-facing change.
> > > 
> > > Signed-off-by: Tyler Hicks <tyhicks@xxxxxxxxxxxxxxxxxxx>
> > > ---
> > > 
> > > * v2
> > >   - Allowed IMA_DIGSIG_REQUIRED, IMA_PERMIT_DIRECTIO,
> > >     IMA_MODSIG_ALLOWED, and IMA_CHECK_BLACKLIST conditionals to be
> > >     present in the rule entry flags for non-buffer hook functions.
> > > 
> > >  security/integrity/ima/ima_policy.c | 13 +++++++++++--
> > >  1 file changed, 11 insertions(+), 2 deletions(-)
> > > 
> > > diff --git a/security/integrity/ima/ima_policy.c b/security/integrity/ima/ima_policy.c
> > > index 8cdca2399d59..43d49ad958fb 100644
> > > --- a/security/integrity/ima/ima_policy.c
> > > +++ b/security/integrity/ima/ima_policy.c
> > > @@ -1000,6 +1000,15 @@ static bool ima_validate_rule(struct ima_rule_entry *entry)
> > >  		case KEXEC_KERNEL_CHECK:
> > >  		case KEXEC_INITRAMFS_CHECK:
> > >  		case POLICY_CHECK:
> > > +			if (entry->flags & ~(IMA_FUNC | IMA_MASK | IMA_FSMAGIC |
> > > +					     IMA_UID | IMA_FOWNER | IMA_FSUUID |
> > > +					     IMA_INMASK | IMA_EUID | IMA_PCR |
> > > +					     IMA_FSNAME | IMA_DIGSIG_REQUIRED |
> > > +					     IMA_PERMIT_DIRECTIO |
> > > +					     IMA_MODSIG_ALLOWED |
> > > +					     IMA_CHECK_BLACKLIST))
> > 
> > Other than KEYRINGS, this patch should continue to behave the same.
> > ÂHowever, this list gives the impressions that all of these flags are
> > permitted on all of the above flags, which isn't true.
> > 
> > For example, both IMA_MODSIG_ALLOWED & IMA_CHECK_BLACKLIST are limited
> > to appended signatures, meaning KERNEL_CHECK and KEXEC_KERNEL_CHECK.
> 
> Just to clarify, are both IMA_MODSIG_ALLOWED and IMA_CHECK_BLACKLIST
> limited to KEXEC_KERNEL_CHECK, KEXEC_INITRAMFS_CHECK, and MODULE_CHECK?
> That's what ima_hook_supports_modsig() suggests.

Theoretically that is true, but I have no idea how you would append a
signature to the kexec boot command line. ÂThe only users of appended
signatures are currently kernel modules and the kexec'ed kernel image.

> 
> > ÂBoth should only be allowed on APPRAISE action rules.
> 
> For completeness, it looks like DONT_APPRAISE should not be allowed.

Good point. Â

> 
> > IMA_PCR should be limited to MEASURE action rules.
> 
> It looks like DONT_MEASURE should not be allowed.

The TPM PCR isn't a file attribute.

> 
> > IMA_DIGSIG_REQUIRED should be limited to APPRAISE action rules.
> 
> It looks like DONT_APPRAISE should not be allowed.

Right, in all of these cases the DONT_XXXX isn't applicable.

Mimi