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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>
This commit is contained in:
Dmitry Kasatkin 2011-05-06 11:34:14 +03:00 committed by Mimi Zohar
parent 2960e6cb5f
commit 6d38ca01c0
1 changed files with 5 additions and 6 deletions
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11
security/integrity/evm/evm_main.c
View File

@ -56,13 +56,15 @@ static enum integrity_status evm_verify_hmac(struct dentry *dentry,
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 @@ 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;
}