Re: [Linux-ima-devel] [PATCH v4 3/5] ima: define "dont_failsafe" policy action rule

[Dmitry Kasatkin <dmitry.kasatkin@gmail.com>]

On Wed, Jul 26, 2017 at 4:22 PM, Mimi Zohar <zohar@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.
>
> Mimi Zohar <zohar@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    | 11 ++++++++++-
>  security/integrity/ima/ima_policy.c  | 29 ++++++++++++++++++++++++++++-
>  4 files changed, 41 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 3941371402ff..664edab0f758 100644
> --- a/security/integrity/ima/ima_main.c
> +++ b/security/integrity/ima/ima_main.c
> @@ -38,6 +38,11 @@ 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();
> @@ -263,8 +268,12 @@ 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 failsaif. 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?


>                 return -EACCES;
> +       }
>         return 0;
>  }
>
> diff --git a/security/integrity/ima/ima_policy.c b/security/integrity/ima/ima_policy.c
> index 95209a5f8595..43b85a4fb8e8 100644
> --- a/security/integrity/ima/ima_policy.c
> +++ b/security/integrity/ima/ima_policy.c
> @@ -40,12 +40,14 @@
>  #define APPRAISE       0x0004  /* same as IMA_APPRAISE */
>  #define DONT_APPRAISE  0x0008
>  #define AUDIT          0x0040
> +#define DONT_FAILSAFE  0x0400
>
>  #define INVALID_PCR(a) (((a) < 0) || \
>         (a) >= (FIELD_SIZEOF(struct integrity_iint_cache, measured_pcrs) * 8))
>
>  int ima_policy_flag;
>  static int temp_ima_appraise;
> +static bool temp_failsafe = 1;
>
>  #define MAX_LSM_RULES 6
>  enum lsm_rule_types { LSM_OBJ_USER, LSM_OBJ_ROLE, LSM_OBJ_TYPE,
> @@ -513,6 +515,9 @@ void ima_update_policy(void)
>         if (ima_rules != policy) {
>                 ima_policy_flag = 0;
>                 ima_rules = policy;
> +
> +               /* Only update on initial policy replacement, not append */
> +               set_failsafe(temp_failsafe);
>         }
>         ima_update_policy_flag();
>  }
> @@ -529,7 +534,7 @@ enum {
>         Opt_uid_gt, Opt_euid_gt, Opt_fowner_gt,
>         Opt_uid_lt, Opt_euid_lt, Opt_fowner_lt,
>         Opt_appraise_type, Opt_permit_directio,
> -       Opt_pcr
> +       Opt_pcr, Opt_dont_failsafe
>  };
>
>  static match_table_t policy_tokens = {
> @@ -560,6 +565,7 @@ static match_table_t policy_tokens = {
>         {Opt_appraise_type, "appraise_type=%s"},
>         {Opt_permit_directio, "permit_directio"},
>         {Opt_pcr, "pcr=%s"},
> +       {Opt_dont_failsafe, "dont_failsafe"},
>         {Opt_err, NULL}
>  };
>
> @@ -630,6 +636,11 @@ static int ima_parse_rule(char *rule, struct ima_rule_entry *entry)
>                 if ((*p == '\0') || (*p == ' ') || (*p == '\t'))
>                         continue;
>                 token = match_token(p, policy_tokens, args);
> +               if (entry->action == DONT_FAILSAFE) {
> +                       /* no args permitted, force invalid rule */
> +                       token = Opt_dont_failsafe;
> +               }
> +
>                 switch (token) {
>                 case Opt_measure:
>                         ima_log_string(ab, "action", "measure");
> @@ -671,6 +682,19 @@ static int ima_parse_rule(char *rule, struct ima_rule_entry *entry)
>
>                         entry->action = AUDIT;
>                         break;
> +               case Opt_dont_failsafe:
> +                       ima_log_string(ab, "action", "dont_failsafe");
> +
> +                       if (entry->action != UNKNOWN)
> +                               result = -EINVAL;
> +
> +                       /* Permit on initial policy replacement only */
> +                       if (ima_rules != &ima_policy_rules)
> +                               temp_failsafe = 0;
> +                       else
> +                               result = -EINVAL;
> +                       entry->action = DONT_FAILSAFE;
> +                       break;
>                 case Opt_func:
>                         ima_log_string(ab, "func", args[0].from);
>
> @@ -949,6 +973,7 @@ void ima_delete_rules(void)
>         int i;
>
>         temp_ima_appraise = 0;
> +       temp_failsafe = 1;
>         list_for_each_entry_safe(entry, tmp, &ima_temp_rules, list) {
>                 for (i = 0; i < MAX_LSM_RULES; i++)
>                         kfree(entry->lsm[i].args_p);
> @@ -1040,6 +1065,8 @@ int ima_policy_show(struct seq_file *m, void *v)
>                 seq_puts(m, pt(Opt_dont_appraise));
>         if (entry->action & AUDIT)
>                 seq_puts(m, pt(Opt_audit));
> +       if (entry->action & DONT_FAILSAFE)
> +               seq_puts(m, pt(Opt_dont_failsafe));
>
>         seq_puts(m, " ");
>
> --
> 2.7.4
>
>
> ------------------------------------------------------------------------------
> Check out the vibrant tech community on one of the world's most
> engaging tech sites, Slashdot.org! http://sdm.link/slashdot
> _______________________________________________
> Linux-ima-devel mailing list
> Linux-ima-devel@lists.sourceforge.net
> https://lists.sourceforge.net/lists/listinfo/linux-ima-devel



-- 
Thanks,
Dmitry