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

[Tyler Hicks]

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.
>  However, 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.

>  Both should only be allowed on APPRAISE action rules.

For completeness, it looks like DONT_APPRAISE should not be allowed.

> IMA_PCR should be limited to MEASURE action rules.

It looks like DONT_MEASURE should not be allowed.

> IMA_DIGSIG_REQUIRED should be limited to APPRAISE action rules.

It looks like DONT_APPRAISE should not be allowed.

> 
> > +				return false;
> > +
> >  			break;
> >  		case KEXEC_CMDLINE:
> >  			if (entry->action & ~(MEASURE | DONT_MEASURE))
> > @@ -1027,7 +1036,8 @@ static bool ima_validate_rule(struct ima_rule_entry *entry)
> >  		default:
> >  			return false;
> >  		}
> > -	}
> > +	} else if (entry->flags & IMA_KEYRINGS)
> > +		return false;
> 
> IMA_MODSIG_ALLOWED and IMA_CHECK_BLACKLIST need to be added here as
> well.

That makes sense.

Tyler

> 
> Mimi
> 
> >  
> >  	return true;
> >  }
> > @@ -1209,7 +1219,6 @@ static int ima_parse_rule(char *rule, struct ima_rule_entry *entry)
> >  			keyrings_len = strlen(args[0].from) + 1;
> >  
> >  			if ((entry->keyrings) ||
> > -			    (entry->func != KEY_CHECK) ||
> >  			    (keyrings_len < 2)) {
> >  				result = -EINVAL;
> >  				break;