evm: evm_verify_hmac must not return INTEGRITY_UNKNOWN
If EVM is not supported or enabled, evm_verify_hmac() returns
INTEGRITY_UNKNOWN, which ima_appraise_measurement() ignores and sets
the appraisal status based solely on the security.ima verification.
evm_verify_hmac() also returns INTEGRITY_UNKNOWN for other failures, such
as temporary failures like -ENOMEM, resulting in possible attack vectors.
This patch changes the default return code for temporary/unexpected
failures, like -ENOMEM, from INTEGRITY_UNKNOWN to INTEGRITY_FAIL, making
evm_verify_hmac() fail safe.
As a result, failures need to be re-evaluated in order to catch both
temporary errors, such as the -ENOMEM, as well as errors that have been
resolved in fix mode.
Signed-off-by: Dmitry Kasatkin <dmitry.kasatkin@nokia.com>
Signed-off-by: Mimi Zohar <zohar@us.ibm.com>
diff --git a/security/integrity/evm/evm_main.c b/security/integrity/evm/evm_main.c
index 0fa8261..bfe44df 100644
--- a/security/integrity/evm/evm_main.c
+++ b/security/integrity/evm/evm_main.c
@@ -56,13 +56,15 @@
struct evm_ima_xattr_data xattr_data;
int rc;
- if (iint->hmac_status != INTEGRITY_UNKNOWN)
+ if (iint->hmac_status == INTEGRITY_PASS)
return iint->hmac_status;
+ /* if status is not PASS, try to check again - against -ENOMEM */
+
rc = evm_calc_hmac(dentry, xattr_name, xattr_value,
xattr_value_len, xattr_data.digest);
if (rc < 0)
- return INTEGRITY_UNKNOWN;
+ goto err_out;
xattr_data.type = EVM_XATTR_HMAC;
rc = vfs_xattr_cmp(dentry, XATTR_NAME_EVM, (u8 *)&xattr_data,
@@ -77,11 +79,8 @@
case -ENODATA: /* file not labelled */
iint->hmac_status = INTEGRITY_NOLABEL;
break;
- case -EINVAL:
- iint->hmac_status = INTEGRITY_FAIL;
- break;
default:
- iint->hmac_status = INTEGRITY_UNKNOWN;
+ iint->hmac_status = INTEGRITY_FAIL;
}
return iint->hmac_status;
}