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[198.145.64.163]) by smtp.gmail.com with ESMTPSA id gm21sm6333686pjb.31.2021.05.14.12.00.19 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 14 May 2021 12:00:20 -0700 (PDT) Date: Fri, 14 May 2021 12:00:19 -0700 From: Kees Cook To: Casey Schaufler Cc: casey.schaufler@intel.com, jmorris@namei.org, linux-security-module@vger.kernel.org, selinux@vger.kernel.org, linux-audit@redhat.com, john.johansen@canonical.com, penguin-kernel@i-love.sakura.ne.jp, paul@paul-moore.com, sds@tycho.nsa.gov, linux-kernel@vger.kernel.org Subject: Re: [PATCH v26 04/25] IMA: avoid label collisions with stacked LSMs Message-ID: <202105141157.DF737E145@keescook> References: <20210513200807.15910-1-casey@schaufler-ca.com> <20210513200807.15910-5-casey@schaufler-ca.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210513200807.15910-5-casey@schaufler-ca.com> Precedence: bulk List-ID: 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 > To: Mimi Zohar > To: linux-integrity@vger.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 -- Kees Cook