Re: [PATCH v8 4/8] IMA: add policy rule to measure critical data

[Tushar Sugandhi]

On 2020-12-11 4:25 p.m., Tyler Hicks wrote:
> On 2020-12-11 15:58:03, Tushar Sugandhi wrote:
> > A new IMA policy rule is needed for the IMA hook
> > ima_measure_critical_data() and the corresponding func CRITICAL_DATA for
> > measuring the input buffer. The policy rule should ensure the buffer
> > would get measured only when the policy rule allows the action. The
> > policy rule should also support the necessary constraints (flags etc.)
> > for integrity critical buffer data measurements.
> >
> > Add a policy rule to define the constraints for restricting integrity
> > critical data measurements.
> >
> > Signed-off-by: Tushar Sugandhi <tusharsu@xxxxxxxxxxxxxxxxxxx>
> > ---
> >   Documentation/ABI/testing/ima_policy |  2 +-
> >   security/integrity/ima/ima_policy.c  | 34 ++++++++++++++++++++++++----
> >   2 files changed, 31 insertions(+), 5 deletions(-)
> >
> > diff --git a/Documentation/ABI/testing/ima_policy b/Documentation/ABI/testing/ima_policy
> > index e35263f97fc1..6ec7daa87cba 100644
> > --- a/Documentation/ABI/testing/ima_policy
> > +++ b/Documentation/ABI/testing/ima_policy
> > @@ -32,7 +32,7 @@ Description:
> >   			func:= [BPRM_CHECK][MMAP_CHECK][CREDS_CHECK][FILE_CHECK]MODULE_CHECK]
> >   			        [FIRMWARE_CHECK]
> >   				[KEXEC_KERNEL_CHECK] [KEXEC_INITRAMFS_CHECK]
> > -				[KEXEC_CMDLINE] [KEY_CHECK]
> > +				[KEXEC_CMDLINE] [KEY_CHECK] [CRITICAL_DATA]
> >   			mask:= [[^]MAY_READ] [[^]MAY_WRITE] [[^]MAY_APPEND]
> >   			       [[^]MAY_EXEC]
> >   			fsmagic:= hex value
> > diff --git a/security/integrity/ima/ima_policy.c b/security/integrity/ima/ima_policy.c
> > index a09d1a41a290..07116ff35c25 100644
> > --- a/security/integrity/ima/ima_policy.c
> > +++ b/security/integrity/ima/ima_policy.c
> > @@ -85,6 +85,7 @@ struct ima_rule_entry {
> >   	} lsm[MAX_LSM_RULES];
> >   	char *fsname;
> >   	struct ima_rule_opt_list *keyrings; /* Measure keys added to these keyrings */
> > +	struct ima_rule_opt_list *data_source; /* Measure data from this source */
>
> Argh, there are still some more instances of data_source sneaking into
> this patch too early instead of waiting until the next patch.
I kept it purposefully in this patch so that the
"case CRITICAL_DATA:" could be properly defined.

Also, my impression was rule->data_source is not part of the user facing
policy.

Whereas IMA_DATA_SOURCE, Opt_data_source, data_source=%s are.
That's why they are part of Patch #5.

Patch #5 IMA: limit critical data measurement based on a label

> >   	struct ima_template_desc *template;
> >   };
> >   
> > @@ -479,6 +480,12 @@ static bool ima_match_rule_data(struct ima_rule_entry *rule,
> >   
> >   		opt_list = rule->keyrings;
> >   		break;
> > +	case CRITICAL_DATA:
> > +		if (!rule->data_source)
> > +			return true;
> > +
> > +		opt_list = rule->data_source;
> > +		break;
>
> I guess this case should unconditionally return true in this patch and
> then the include this additional logic in the next patch.
>
> Sorry, I missed these on my last review.
No worries.

As I mentioned above, I kept it purposefully in this patch since
my impression was rule->data_source is not part of the user facing
policy.

But I can simply return true here as you suggested, and move the logic 
to the next patch.

+	case CRITICAL_DATA:
+		if (!rule->data_source)
+			return true;
+
+		opt_list = rule->data_source;
+		break;


~Tushar