[PATCH v6 5/6] ima: define "dont_failsafe" policy action rule

[Dmitry Kasatkin]

On Tue, Aug 22, 2017 at 3:54 PM, Mimi Zohar <zohar at linux.vnet.ibm.com> wrote:
> On Tue, 2017-08-22 at 13:07 +0300, Dmitry Kasatkin wrote:
>> On Tue, Aug 15, 2017 at 5:43 PM, Mimi Zohar <zohar at linux.vnet.ibm.com> wrote:
>> > Permit normally denied access/execute permission for files in policy
>> > on IMA unsupported filesystems.  This patch defines the "dont_failsafe"
>> > policy action rule.
>> >
>> > Signed-off-by: Mimi Zohar <zohar at linux.vnet.ibm.com>
>> >
>> > ---
>> > Changelog v3:
>> > - include dont_failsafe rule when displaying policy
>> > - fail attempt to add dont_failsafe rule when appending to the policy
>> >
>> >  Documentation/ABI/testing/ima_policy |  3 ++-
>> >  security/integrity/ima/ima.h         |  1 +
>> >  security/integrity/ima/ima_main.c    | 12 +++++++++++-
>> >  security/integrity/ima/ima_policy.c  | 29 ++++++++++++++++++++++++++++-
>> >  4 files changed, 42 insertions(+), 3 deletions(-)
>> >
>> > diff --git a/Documentation/ABI/testing/ima_policy b/Documentation/ABI/testing/ima_policy
>> > index e76432b9954d..f271207743e5 100644
>> > --- a/Documentation/ABI/testing/ima_policy
>> > +++ b/Documentation/ABI/testing/ima_policy
>> > @@ -17,7 +17,8 @@ Description:
>> >
>> >                 rule format: action [condition ...]
>> >
>> > -               action: measure | dont_measure | appraise | dont_appraise | audit
>> > +               action: measure | dont_meaure | appraise | dont_appraise |
>> > +                       audit | dont_failsafe
>> >                 condition:= base | lsm  [option]
>> >                         base:   [[func=] [mask=] [fsmagic=] [fsuuid=] [uid=]
>> >                                 [euid=] [fowner=]]
>> > diff --git a/security/integrity/ima/ima.h b/security/integrity/ima/ima.h
>> > index d52b487ad259..c5f34f7c5b0f 100644
>> > --- a/security/integrity/ima/ima.h
>> > +++ b/security/integrity/ima/ima.h
>> > @@ -224,6 +224,7 @@ void *ima_policy_start(struct seq_file *m, loff_t *pos);
>> >  void *ima_policy_next(struct seq_file *m, void *v, loff_t *pos);
>> >  void ima_policy_stop(struct seq_file *m, void *v);
>> >  int ima_policy_show(struct seq_file *m, void *v);
>> > +void set_failsafe(bool flag);
>> >
>> >  /* Appraise integrity measurements */
>> >  #define IMA_APPRAISE_ENFORCE   0x01
>> > diff --git a/security/integrity/ima/ima_main.c b/security/integrity/ima/ima_main.c
>> > index d23dfe6ede18..b00186914df8 100644
>> > --- a/security/integrity/ima/ima_main.c
>> > +++ b/security/integrity/ima/ima_main.c
>> > @@ -38,6 +38,12 @@ int ima_appraise;
>> >  int ima_hash_algo = HASH_ALGO_SHA1;
>> >  static int hash_setup_done;
>> >
>> > +static bool ima_failsafe = 1;
>> > +void set_failsafe(bool flag)
>> > +{
>> > +       ima_failsafe = flag;
>> > +}
>> > +
>> >  static int __init hash_setup(char *str)
>> >  {
>> >         struct ima_template_desc *template_desc = ima_template_desc_current();
>> > @@ -260,8 +266,12 @@ static int process_measurement(struct file *file, char *buf, loff_t size,
>> >                 __putname(pathbuf);
>> >  out:
>> >         inode_unlock(inode);
>> > -       if ((rc && must_appraise) && (ima_appraise & IMA_APPRAISE_ENFORCE))
>> > +       if ((rc && must_appraise) && (ima_appraise & IMA_APPRAISE_ENFORCE)) {
>> > +               if (!ima_failsafe && rc == -EBADF)
>> > +                       return 0;
>> > +
>>
>> By default IMA is failsafe. ima_failsafe is true.
>> Return 0 is needed in failsafe mode. right?
>> But in this logic it will happen if ima_failsafe is false. meaning it
>> is not failsafe.
>>
>> Is it a typo?
>
> No, the default, as you pointed out above, is failsafe mode.  Only when we are not in failsafe mode, do we allow the file access/execute for file's that we could not appraise.
>
> Mimi
>

So in your language "failsafe" means IMA must fail/return with error
on failure..

Ok. then logic is correct and OK with me.


-- 
Thanks,
Dmitry
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