Re: [PATCH v35 05/29] IMA: avoid label collisions with stacked LSMs

John Johansen
2022-04-21T16:50:29Z

On 4/18/22 07:59, 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 security 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@schaufler-ca.com>

Reviewed-by: John Johansen <john.johansen@canonical.com>

> To: Mimi Zohar <zohar@linux.ibm.com>
> To: linux-integrity@vger.kernel.org
> ---
> Documentation/ABI/testing/ima_policy | 8 ++++-
> include/linux/security.h | 14 ++++----
> security/integrity/ima/ima_policy.c | 51 ++++++++++++++++++++++++----
> security/security.c | 35 +++++++++++++++----
> 4 files changed, 89 insertions(+), 19 deletions(-)
>
> diff --git a/Documentation/ABI/testing/ima_policy b/Documentation/ABI/testing/ima_policy
> index 839fab811b18..64863e9d87ea 100644
> --- a/Documentation/ABI/testing/ima_policy
> +++ b/Documentation/ABI/testing/ima_policy
> @@ -26,7 +26,7 @@ Description:
> [uid=] [euid=] [gid=] [egid=]
> [fowner=] [fgroup=]]
> 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=] [appraise_algos=] [keyrings=]
> base:
> @@ -126,6 +126,12 @@ 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
> + module 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/include/linux/security.h b/include/linux/security.h
> index d00870d2b416..3666eddad59a 100644
> --- a/include/linux/security.h
> +++ b/include/linux/security.h
> @@ -1985,25 +1985,27 @@ static inline void security_audit_rule_free(struct audit_lsm_rules *lsmrules)
> #endif /* CONFIG_AUDIT */
>
> #if defined(CONFIG_IMA_LSM_RULES) && defined(CONFIG_SECURITY)
> -int ima_filter_rule_init(u32 field, u32 op, char *rulestr, void **lsmrule);
> -int ima_filter_rule_match(u32 secid, u32 field, u32 op, void *lsmrule);
> -void ima_filter_rule_free(void *lsmrule);
> +int ima_filter_rule_init(u32 field, u32 op, char *rulestr, void **lsmrule,
> + int lsmslot);
> +int ima_filter_rule_match(u32 secid, u32 field, u32 op, void *lsmrule,
> + int lsmslot);
> +void ima_filter_rule_free(void *lsmrule, int lsmslot);
>
> #else
>
> static inline int ima_filter_rule_init(u32 field, u32 op, char *rulestr,
> - void **lsmrule)
> + void **lsmrule, int lsmslot)
> {
> return 0;
> }
>
> static inline int ima_filter_rule_match(u32 secid, u32 field, u32 op,
> - void *lsmrule)
> + void *lsmrule, int lsmslot)
> {
> return 0;
> }
>
> -static inline void ima_filter_rule_free(void *lsmrule)
> +static inline void ima_filter_rule_free(void *lsmrule, int lsmslot)
> { }
>
> #endif /* defined(CONFIG_IMA_LSM_RULES) && defined(CONFIG_SECURITY) */
> diff --git a/security/integrity/ima/ima_policy.c b/security/integrity/ima/ima_policy.c
> index eea6e92500b8..97470354c8ae 100644
> --- a/security/integrity/ima/ima_policy.c
> +++ b/security/integrity/ima/ima_policy.c
> @@ -89,6 +89,7 @@ struct ima_rule_entry {
> bool (*fgroup_op)(kgid_t cred_gid, kgid_t rule_gid); /* gid_eq(), gid_gt(), gid_lt() */
> int pcr;
> unsigned int allowed_algos; /* bitfield of allowed hash algorithms */
> + int which; /* which LSM rule applies to */
> struct {
> void *rule; /* LSM file metadata specific */
> char *args_p; /* audit value */
> @@ -285,6 +286,20 @@ 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;
> @@ -356,7 +371,7 @@ static void ima_lsm_free_rule(struct ima_rule_entry *entry)
> int i;
>
> for (i = 0; i < MAX_LSM_RULES; i++) {
> - ima_filter_rule_free(entry->lsm[i].rule);
> + ima_filter_rule_free(entry->lsm[i].rule, entry->which);
> kfree(entry->lsm[i].args_p);
> }
> }
> @@ -407,7 +422,8 @@ 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].rule);
> + &nentry->lsm[i].rule,
> + entry->which);
> if (!nentry->lsm[i].rule)
> pr_warn("rule for LSM \'%s\' is undefined\n",
> nentry->lsm[i].args_p);
> @@ -623,14 +639,16 @@ 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].rule);
> + rule->lsm[i].rule,
> + rule->which);
> 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].rule);
> + rule->lsm[i].rule,
> + rule->which);
> break;
> default:
> break;
> @@ -1025,7 +1043,7 @@ enum policy_opt {
> Opt_fowner_lt, Opt_fgroup_lt,
> Opt_appraise_type, Opt_appraise_flag, Opt_appraise_algos,
> 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 = {
> @@ -1073,6 +1091,7 @@ 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}
> };
>
> @@ -1091,7 +1110,8 @@ 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].rule);
> + &entry->lsm[lsm_rule].rule,
> + entry->which);
> if (!entry->lsm[lsm_rule].rule) {
> pr_warn("rule for LSM \'%s\' is undefined\n",
> entry->lsm[lsm_rule].args_p);
> @@ -1780,6 +1800,19 @@ 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 = result;
> + result = 0;
> + break;
> case Opt_err:
> ima_log_string(ab, "UNKNOWN", p);
> result = -EINVAL;
> @@ -1816,6 +1849,7 @@ 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;
> @@ -1833,6 +1867,9 @@ ssize_t ima_parse_add_rule(char *rule)
>
> INIT_LIST_HEAD(&entry->list);
>
> + for (i = 0; i < MAX_LSM_RULES; i++)
> + entry->which = ima_rules_lsm;
> +
> result = ima_parse_rule(p, entry);
> if (result) {
> ima_free_rule(entry);
> @@ -2158,6 +2195,8 @@ 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 >= 0)
> + seq_printf(m, pt(Opt_lsm), lsm_slot_to_name(entry->which));
> rcu_read_unlock();
> seq_puts(m, "\n");
> return 0;
> diff --git a/security/security.c b/security/security.c
> index d1ddbb857af1..9e0139b0d346 100644
> --- a/security/security.c
> +++ b/security/security.c
> @@ -2728,19 +2728,42 @@ int security_audit_rule_match(u32 secid, u32 field, u32 op,
> * The integrity subsystem uses the same hooks as
> * the audit subsystem.
> */
> -int ima_filter_rule_init(u32 field, u32 op, char *rulestr, void **lsmrule)
> +int ima_filter_rule_init(u32 field, u32 op, char *rulestr, void **lsmrule,
> + int lsmslot)
> {
> - return call_int_hook(audit_rule_init, 0, field, op, rulestr, lsmrule);
> + struct security_hook_list *hp;
> +
> + hlist_for_each_entry(hp, &security_hook_heads.audit_rule_init, list)
> + if (hp->lsmid->slot == lsmslot)
> + return hp->hook.audit_rule_init(field, op, rulestr,
> + lsmrule);
> +
> + return 0;
> }
>
> -void ima_filter_rule_free(void *lsmrule)
> +void ima_filter_rule_free(void *lsmrule, int lsmslot)
> {
> - call_void_hook(audit_rule_free, lsmrule);
> + struct security_hook_list *hp;
> +
> + hlist_for_each_entry(hp, &security_hook_heads.audit_rule_free, list) {
> + if (hp->lsmid->slot == lsmslot) {
> + hp->hook.audit_rule_free(lsmrule);
> + return;
> + }
> + }
> }
>
> -int ima_filter_rule_match(u32 secid, u32 field, u32 op, void *lsmrule)
> +int ima_filter_rule_match(u32 secid, u32 field, u32 op, void *lsmrule,
> + int lsmslot)
> {
> - return call_int_hook(audit_rule_match, 0, secid, field, op, lsmrule);
> + struct security_hook_list *hp;
> +
> + hlist_for_each_entry(hp, &security_hook_heads.audit_rule_match, list)
> + if (hp->lsmid->slot == lsmslot)
> + return hp->hook.audit_rule_match(secid, field, op,
> + lsmrule);
> +
> + return 0;
> }
> #endif /* CONFIG_IMA_LSM_RULES */
>