security/integrity: Harden against malformed xattrs

In general the handling of IMA/EVM xattrs is good, but I found
a few locations where either the xattr size or the value of the
type field in the xattr are not checked. Add a few simple checks
to these locations to prevent malformed or malicious xattrs from
causing problems.
Signed-off-by: Seth Forshee <seth.forshee@canonical.com>
Signed-off-by: Mimi Zohar <zohar@linux.vnet.ibm.com>

security/integrity/digsig.c

@@ -51,7 +51,7 @@ static bool init_keyring __initdata;
 int integrity_digsig_verify(const unsigned int id, const char *sig, int siglen,
 			    const char *digest, int digestlen)
 {
-	if (id >= INTEGRITY_KEYRING_MAX)
+	if (id >= INTEGRITY_KEYRING_MAX || siglen < 2)
 		return -EINVAL;
 
 	if (!keyring[id]) {

security/integrity/evm/evm_main.c

@@ -145,6 +145,10 @@ static enum integrity_status evm_verify_hmac(struct dentry *dentry,
 	/* check value type */
 	switch (xattr_data->type) {
 	case EVM_XATTR_HMAC:
+		if (xattr_len != sizeof(struct evm_ima_xattr_data)) {
+			evm_status = INTEGRITY_FAIL;
+			goto out;
+		}
 		rc = evm_calc_hmac(dentry, xattr_name, xattr_value,
 				   xattr_value_len, calc.digest);
 		if (rc)

security/integrity/ima/ima_appraise.c

@@ -130,6 +130,7 @@ enum hash_algo ima_get_hash_algo(struct evm_ima_xattr_data *xattr_value,
 				 int xattr_len)
 {
 	struct signature_v2_hdr *sig;
+	enum hash_algo ret;
 
 	if (!xattr_value || xattr_len < 2)
 		/* return default hash algo */
@@ -143,7 +144,9 @@ enum hash_algo ima_get_hash_algo(struct evm_ima_xattr_data *xattr_value,
 		return sig->hash_algo;
 		break;
 	case IMA_XATTR_DIGEST_NG:
-		return xattr_value->digest[0];
+		ret = xattr_value->digest[0];
+		if (ret < HASH_ALGO__LAST)
+			return ret;
 		break;
 	case IMA_XATTR_DIGEST:
 		/* this is for backward compatibility */