ima: Move comprehensive rule validation checks out of the token parser

Use ima_validate_rule(), at the end of the token parsing stage, to
verify combinations of actions, hooks, and flags. This is useful to
increase readability by consolidating such checks into a single function
and also because rule conditionals can be specified in arbitrary order
making it difficult to do comprehensive rule validation until the entire
rule has been parsed.

This allows for the check that ties together the "keyrings" conditional
with the KEY_CHECK function hook to be moved into the final rule
validation.

The modsig check no longer needs to compiled conditionally because the
token parser will ensure that modsig support is enabled before accepting
"imasig|modsig" appraise type values. The final rule validation will
ensure that appraise_type and appraise_flag options are only present in
appraise rules.

Finally, this allows for the check that ties together the "pcr"
conditional with the measure action to be moved into the final rule
validation.

Signed-off-by: Tyler Hicks <[e-mail]>
Signed-off-by: Mimi Zohar <[e-mail]>

security/integrity/ima/ima.h

···
 #endif /* CONFIG_IMA_APPRAISE */
 
 #ifdef CONFIG_IMA_APPRAISE_MODSIG
-bool ima_hook_supports_modsig(enum ima_hooks func);
 int ima_read_modsig(enum ima_hooks func, const void *buf, loff_t buf_len,
 		    struct modsig **modsig);
 void ima_collect_modsig(struct modsig *modsig, const void *buf, loff_t size);
···
 		       u32 *data_len);
 void ima_free_modsig(struct modsig *modsig);
 #else
-static inline bool ima_hook_supports_modsig(enum ima_hooks func)
-{
-	return false;
-}
-
 static inline int ima_read_modsig(enum ima_hooks func, const void *buf,
 				  loff_t buf_len, struct modsig **modsig)
 {

security/integrity/ima/ima_modsig.c

···
 	u8 raw_pkcs7[];
 };
 
-/**
- * ima_hook_supports_modsig - can the policy allow modsig for this hook?
- *
- * modsig is only supported by hooks using ima_post_read_file(), because only
- * they preload the contents of the file in a buffer. FILE_CHECK does that in
- * some cases, but not when reached from vfs_open(). POLICY_CHECK can support
- * it, but it's not useful in practice because it's a text file so deny.
- */
-bool ima_hook_supports_modsig(enum ima_hooks func)
-{
-	switch (func) {
-	case KEXEC_KERNEL_CHECK:
-	case KEXEC_INITRAMFS_CHECK:
-	case MODULE_CHECK:
-		return true;
-	default:
-		return false;
-	}
-}
-
 /*
  * ima_read_modsig - Read modsig from buf.
  *

security/integrity/ima/ima_policy.c

···
 
 static bool ima_validate_rule(struct ima_rule_entry *entry)
 {
-	/* Ensure that the action is set */
+	/* Ensure that the action is set and is compatible with the flags */
 	if (entry->action == UNKNOWN)
+		return false;
+
+	if (entry->action != MEASURE && entry->flags & IMA_PCR)
+		return false;
+
+	if (entry->action != APPRAISE &&
+	    entry->flags & (IMA_DIGSIG_REQUIRED | IMA_MODSIG_ALLOWED | IMA_CHECK_BLACKLIST))
+		return false;
+
+	/*
+	 * The IMA_FUNC bit must be set if and only if there's a valid hook
+	 * function specified, and vice versa. Enforcing this property allows
+	 * for the NONE case below to validate a rule without an explicit hook
+	 * function.
+	 */
+	if (((entry->flags & IMA_FUNC) && entry->func == NONE) ||
+	    (!(entry->flags & IMA_FUNC) && entry->func != NONE))
 		return false;
 
 	/*
···
 	case BPRM_CHECK:
 	case CREDS_CHECK:
 	case POST_SETATTR:
-	case MODULE_CHECK:
 	case FIRMWARE_CHECK:
+	case POLICY_CHECK:
+		if (entry->flags & ~(IMA_FUNC | IMA_MASK | IMA_FSMAGIC |
+				     IMA_UID | IMA_FOWNER | IMA_FSUUID |
+				     IMA_INMASK | IMA_EUID | IMA_PCR |
+				     IMA_FSNAME | IMA_DIGSIG_REQUIRED |
+				     IMA_PERMIT_DIRECTIO))
+			return false;
+
+		break;
+	case MODULE_CHECK:
 	case KEXEC_KERNEL_CHECK:
 	case KEXEC_INITRAMFS_CHECK:
-	case POLICY_CHECK:
-		/* Validation of these hook functions is in ima_parse_rule() */
+		if (entry->flags & ~(IMA_FUNC | IMA_MASK | IMA_FSMAGIC |
+				     IMA_UID | IMA_FOWNER | IMA_FSUUID |
+				     IMA_INMASK | IMA_EUID | IMA_PCR |
+				     IMA_FSNAME | IMA_DIGSIG_REQUIRED |
+				     IMA_PERMIT_DIRECTIO | IMA_MODSIG_ALLOWED |
+				     IMA_CHECK_BLACKLIST))
+			return false;
+
 		break;
 	case KEXEC_CMDLINE:
 		if (entry->action & ~(MEASURE | DONT_MEASURE))
···
 			keyrings_len = strlen(args[0].from) + 1;
 
 			if ((entry->keyrings) ||
-			    (entry->func != KEY_CHECK) ||
 			    (keyrings_len < 2)) {
 				result = -EINVAL;
 				break;
···
 						   AUDIT_SUBJ_TYPE);
 			break;
 		case Opt_appraise_type:
-			if (entry->action != APPRAISE) {
-				result = -EINVAL;
-				break;
-			}
-
 			ima_log_string(ab, "appraise_type", args[0].from);
 			if ((strcmp(args[0].from, "imasig")) == 0)
 				entry->flags |= IMA_DIGSIG_REQUIRED;
-			else if (ima_hook_supports_modsig(entry->func) &&
+			else if (IS_ENABLED(CONFIG_IMA_APPRAISE_MODSIG) &&
 				 strcmp(args[0].from, "imasig|modsig") == 0)
 				entry->flags |= IMA_DIGSIG_REQUIRED |
 						IMA_MODSIG_ALLOWED;
···
 				result = -EINVAL;
 			break;
 		case Opt_appraise_flag:
-			if (entry->action != APPRAISE) {
-				result = -EINVAL;
-				break;
-			}
-
 			ima_log_string(ab, "appraise_flag", args[0].from);
 			if (IS_ENABLED(CONFIG_IMA_APPRAISE_MODSIG) &&
 			    strstr(args[0].from, "blacklist"))
···
 			entry->flags |= IMA_PERMIT_DIRECTIO;
 			break;
 		case Opt_pcr:
-			if (entry->action != MEASURE) {
-				result = -EINVAL;
-				break;
-			}
 			ima_log_string(ab, "pcr", args[0].from);
 
 			result = kstrtoint(args[0].from, 10, &entry->pcr);