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Message-ID: <202105141157.DF737E145@keescook>
Date: Fri, 14 May 2021 12:00:19 -0700
From: Kees Cook <keescook@...omium.org>
To: Casey Schaufler <casey@...aufler-ca.com>
Cc: casey.schaufler@...el.com, jmorris@...ei.org,
linux-security-module@...r.kernel.org, selinux@...r.kernel.org,
linux-audit@...hat.com, john.johansen@...onical.com,
penguin-kernel@...ove.sakura.ne.jp, paul@...l-moore.com,
sds@...ho.nsa.gov, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v26 04/25] IMA: avoid label collisions with stacked LSMs
On Thu, May 13, 2021 at 01:07:46PM -0700, Casey Schaufler wrote:
> Integrity measurement may filter on security module information
> and needs to be clear in the case of multiple active security
> modules which applies. Provide a boot option ima_rules_lsm= to
> allow the user to specify an active securty module to apply
> filters to. If not specified, use the first registered module
> that supports the audit_rule_match() LSM hook. Allow the user
> to specify in the IMA policy an lsm= option to specify the
> security module to use for a particular rule.
>
> Signed-off-by: Casey Schaufler <casey@...aufler-ca.com>
> To: Mimi Zohar <zohar@...ux.ibm.com>
> To: linux-integrity@...r.kernel.org
> ---
> Documentation/ABI/testing/ima_policy | 8 ++-
> security/integrity/ima/ima_policy.c | 77 ++++++++++++++++++++--------
> 2 files changed, 62 insertions(+), 23 deletions(-)
>
> diff --git a/Documentation/ABI/testing/ima_policy b/Documentation/ABI/testing/ima_policy
> index 070779e8d836..84dd19bc4344 100644
> --- a/Documentation/ABI/testing/ima_policy
> +++ b/Documentation/ABI/testing/ima_policy
> @@ -25,7 +25,7 @@ Description:
> base: [[func=] [mask=] [fsmagic=] [fsuuid=] [uid=]
> [euid=] [fowner=] [fsname=]]
> lsm: [[subj_user=] [subj_role=] [subj_type=]
> - [obj_user=] [obj_role=] [obj_type=]]
> + [obj_user=] [obj_role=] [obj_type=] [lsm=]]
> option: [[appraise_type=]] [template=] [permit_directio]
> [appraise_flag=] [keyrings=]
> base:
> @@ -117,6 +117,12 @@ Description:
>
> measure subj_user=_ func=FILE_CHECK mask=MAY_READ
>
> + It is possible to explicitly specify which security
> + module a rule applies to using lsm=. If the security
> + modules specified is not active on the system the rule
> + will be rejected. If lsm= is not specified the first
> + security module registered on the system will be assumed.
> +
> Example of measure rules using alternate PCRs::
>
> measure func=KEXEC_KERNEL_CHECK pcr=4
> diff --git a/security/integrity/ima/ima_policy.c b/security/integrity/ima/ima_policy.c
> index 5c40677e881c..d804b9a0dd95 100644
> --- a/security/integrity/ima/ima_policy.c
> +++ b/security/integrity/ima/ima_policy.c
> @@ -79,8 +79,9 @@ struct ima_rule_entry {
> bool (*uid_op)(kuid_t, kuid_t); /* Handlers for operators */
> bool (*fowner_op)(kuid_t, kuid_t); /* uid_eq(), uid_gt(), uid_lt() */
> int pcr;
> + int which_lsm; /* which of the rules to use */
> struct {
> - void *rules[LSMBLOB_ENTRIES]; /* LSM file metadata specific */
> + void *rule; /* LSM file metadata specific */
> char *args_p; /* audit value */
> int type; /* audit type */
> } lsm[MAX_LSM_RULES];
> @@ -92,17 +93,15 @@ struct ima_rule_entry {
>
> /**
> * ima_lsm_isset - Is a rule set for any of the active security modules
> - * @rules: The set of IMA rules to check
> + * @entry: the rule entry to examine
> + * @lsm_rule: the specific rule type in question
> *
> - * If a rule is set for any LSM return true, otherwise return false.
> + * If a rule is set return true, otherwise return false.
> */
> -static inline bool ima_lsm_isset(void *rules[])
> +static inline bool ima_lsm_isset(struct ima_rule_entry *entry, int lsm_rule)
> {
> - int i;
> -
> - for (i = 0; i < LSMBLOB_ENTRIES; i++)
> - if (rules[i])
> - return true;
> + if (entry->lsm[lsm_rule].rule)
> + return true;
I'd be happier if this retained the MAX_LSM_RULES bounds-check.
> return false;
> }
>
> @@ -282,6 +281,20 @@ static int __init default_appraise_policy_setup(char *str)
> }
> __setup("ima_appraise_tcb", default_appraise_policy_setup);
>
> +static int ima_rules_lsm __ro_after_init;
> +
> +static int __init ima_rules_lsm_init(char *str)
> +{
> + ima_rules_lsm = lsm_name_to_slot(str);
> + if (ima_rules_lsm < 0) {
> + ima_rules_lsm = 0;
> + pr_err("rule lsm \"%s\" not registered", str);
> + }
> +
> + return 1;
> +}
> +__setup("ima_rules_lsm=", ima_rules_lsm_init);
> +
> static struct ima_rule_opt_list *ima_alloc_rule_opt_list(const substring_t *src)
> {
> struct ima_rule_opt_list *opt_list;
> @@ -351,11 +364,10 @@ static void ima_free_rule_opt_list(struct ima_rule_opt_list *opt_list)
> static void ima_lsm_free_rule(struct ima_rule_entry *entry)
> {
> int i;
> - int r;
>
> for (i = 0; i < MAX_LSM_RULES; i++) {
> - for (r = 0; r < LSMBLOB_ENTRIES; r++)
> - ima_filter_rule_free(entry->lsm[i].rules[r]);
> + if (entry->lsm[i].rule)
> + ima_filter_rule_free(entry->lsm[i].rule);
> kfree(entry->lsm[i].args_p);
> }
> }
> @@ -406,8 +418,8 @@ static struct ima_rule_entry *ima_lsm_copy_rule(struct ima_rule_entry *entry)
>
> ima_filter_rule_init(nentry->lsm[i].type, Audit_equal,
> nentry->lsm[i].args_p,
> - &nentry->lsm[i].rules[0]);
> - if (!ima_lsm_isset(nentry->lsm[i].rules))
> + &nentry->lsm[i].rule);
> + if (!ima_lsm_isset(nentry, i))
> pr_warn("rule for LSM \'%s\' is undefined\n",
> nentry->lsm[i].args_p);
> }
> @@ -596,7 +608,7 @@ static bool ima_match_rules(struct ima_rule_entry *rule,
> int rc = 0;
> u32 osid;
>
> - if (!ima_lsm_isset(rule->lsm[i].rules)) {
> + if (!ima_lsm_isset(rule, i)) {
> if (!rule->lsm[i].args_p)
> continue;
> else
> @@ -609,14 +621,14 @@ static bool ima_match_rules(struct ima_rule_entry *rule,
> security_inode_getsecid(inode, &osid);
> rc = ima_filter_rule_match(osid, rule->lsm[i].type,
> Audit_equal,
> - rule->lsm[i].rules);
> + rule->lsm[i].rule);
> break;
> case LSM_SUBJ_USER:
> case LSM_SUBJ_ROLE:
> case LSM_SUBJ_TYPE:
> rc = ima_filter_rule_match(secid, rule->lsm[i].type,
> Audit_equal,
> - rule->lsm[i].rules);
> + rule->lsm[i].rule);
> break;
> default:
> break;
> @@ -966,7 +978,7 @@ enum {
> Opt_uid_lt, Opt_euid_lt, Opt_fowner_lt,
> Opt_appraise_type, Opt_appraise_flag,
> Opt_permit_directio, Opt_pcr, Opt_template, Opt_keyrings,
> - Opt_label, Opt_err
> + Opt_lsm, Opt_label, Opt_err
> };
>
> static const match_table_t policy_tokens = {
> @@ -1004,6 +1016,7 @@ static const match_table_t policy_tokens = {
> {Opt_template, "template=%s"},
> {Opt_keyrings, "keyrings=%s"},
> {Opt_label, "label=%s"},
> + {Opt_lsm, "lsm=%s"},
> {Opt_err, NULL}
> };
>
> @@ -1012,7 +1025,7 @@ static int ima_lsm_rule_init(struct ima_rule_entry *entry,
> {
> int result;
>
> - if (ima_lsm_isset(entry->lsm[lsm_rule].rules))
> + if (ima_lsm_isset(entry, lsm_rule))
> return -EINVAL;
>
> entry->lsm[lsm_rule].args_p = match_strdup(args);
> @@ -1022,8 +1035,8 @@ static int ima_lsm_rule_init(struct ima_rule_entry *entry,
> entry->lsm[lsm_rule].type = audit_type;
> result = ima_filter_rule_init(entry->lsm[lsm_rule].type, Audit_equal,
> entry->lsm[lsm_rule].args_p,
> - &entry->lsm[lsm_rule].rules[0]);
> - if (!ima_lsm_isset(entry->lsm[lsm_rule].rules)) {
> + &entry->lsm[lsm_rule].rule);
> + if (!ima_lsm_isset(entry, lsm_rule)) {
> pr_warn("rule for LSM \'%s\' is undefined\n",
> entry->lsm[lsm_rule].args_p);
>
> @@ -1561,6 +1574,19 @@ static int ima_parse_rule(char *rule, struct ima_rule_entry *entry)
> &(template_desc->num_fields));
> entry->template = template_desc;
> break;
> + case Opt_lsm:
> + result = lsm_name_to_slot(args[0].from);
> + if (result == LSMBLOB_INVALID) {
> + int i;
> +
> + for (i = 0; i < MAX_LSM_RULES; i++)
> + entry->lsm[i].args_p = NULL;
> + result = -EINVAL;
> + break;
> + }
> + entry->which_lsm = result;
> + result = 0;
> + break;
> case Opt_err:
> ima_log_string(ab, "UNKNOWN", p);
> result = -EINVAL;
> @@ -1597,6 +1623,7 @@ ssize_t ima_parse_add_rule(char *rule)
> struct ima_rule_entry *entry;
> ssize_t result, len;
> int audit_info = 0;
> + int i;
>
> p = strsep(&rule, "\n");
> len = strlen(p) + 1;
> @@ -1614,6 +1641,9 @@ ssize_t ima_parse_add_rule(char *rule)
>
> INIT_LIST_HEAD(&entry->list);
>
> + for (i = 0; i < MAX_LSM_RULES; i++)
> + entry->which_lsm = ima_rules_lsm;
> +
> result = ima_parse_rule(p, entry);
> if (result) {
> ima_free_rule(entry);
> @@ -1830,7 +1860,7 @@ int ima_policy_show(struct seq_file *m, void *v)
> }
>
> for (i = 0; i < MAX_LSM_RULES; i++) {
> - if (ima_lsm_isset(entry->lsm[i].rules)) {
> + if (ima_lsm_isset(entry, i)) {
> switch (i) {
> case LSM_OBJ_USER:
> seq_printf(m, pt(Opt_obj_user),
> @@ -1872,6 +1902,9 @@ int ima_policy_show(struct seq_file *m, void *v)
> seq_puts(m, "appraise_flag=check_blacklist ");
> if (entry->flags & IMA_PERMIT_DIRECTIO)
> seq_puts(m, "permit_directio ");
> + if (entry->which_lsm >= 0)
> + seq_printf(m, pt(Opt_lsm),
> + lsm_slot_to_name(entry->which_lsm));
> rcu_read_unlock();
> seq_puts(m, "\n");
> return 0;
> --
> 2.29.2
>
Otherwise, this looks correct. With bounds checking:
Reviewed-by: Kees Cook <keescook@...omium.org>
--
Kees Cook
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