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Subject[PATCH v5 18/21] evm: evm_verify_hmac must not return INTEGRITY_UNKNOWN
Date
From: Dmitry Kasatkin <dmitry.kasatkin@nokia.com>

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>
---
security/integrity/evm/evm_main.c | 11 +++++------
1 files changed, 5 insertions(+), 6 deletions(-)
diff --git a/security/integrity/evm/evm_main.c b/security/integrity/evm/evm_main.c
index 944783c..245ef23 100644
--- a/security/integrity/evm/evm_main.c
+++ b/security/integrity/evm/evm_main.c
@@ -57,14 +57,16 @@ static enum integrity_status evm_verify_hmac(struct dentry *dentry,
char hmac_val[MAX_DIGEST_SIZE + 1];
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 */
+
memset(hmac_val, 0, sizeof hmac_val);
rc = evm_calc_hmac(dentry, xattr_name, xattr_value,
xattr_value_len, hmac_val + 1);
if (rc < 0)
- return INTEGRITY_UNKNOWN;
+ goto err_out;

hmac_val[0] = EVM_XATTR_HMAC;
rc = vfs_xattr_cmp(dentry, XATTR_NAME_EVM, hmac_val, sizeof hmac_val,
@@ -79,11 +81,8 @@ err_out:
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;
}
--
1.7.3.4


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