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Date: Tue, 25 Jan 2022 19:06:57 -0500
From: Mimi Zohar <zohar@...ux.ibm.com>
To: linux-integrity@...r.kernel.org
Cc: Mimi Zohar <zohar@...ux.ibm.com>,
Eric Biggers <ebiggers@...nel.org>,
Stefan Berger <stefanb@...ux.ibm.com>,
linux-fscrypt@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH v3 7/8] ima: support fs-verity file digest based version 3 signatures
Instead of calculating a file hash and verifying the signature stored
in the security.ima xattr against the calculated file hash, verify
fs-verity's signature (version 3).
To differentiate between a regular file hash and an fs-verity file digest
based signature stored as security.ima xattr, define a new signature type
named IMA_VERITY_DIGSIG.
Update the 'ima-sig' template field to display the new fs-verity signature
type as well.
For example:
appraise func=BPRM_CHECK digest_type=hash|verity
Signed-off-by: Mimi Zohar <zohar@...ux.ibm.com>
---
Documentation/ABI/testing/ima_policy | 10 +++++
Documentation/security/IMA-templates.rst | 4 +-
security/integrity/ima/ima_appraise.c | 49 ++++++++++++++++++++++-
security/integrity/ima/ima_template_lib.c | 3 +-
security/integrity/integrity.h | 5 ++-
5 files changed, 65 insertions(+), 6 deletions(-)
diff --git a/Documentation/ABI/testing/ima_policy b/Documentation/ABI/testing/ima_policy
index 444bb7ccbe03..fadf90dde289 100644
--- a/Documentation/ABI/testing/ima_policy
+++ b/Documentation/ABI/testing/ima_policy
@@ -151,6 +151,16 @@ Description:
appraise func=SETXATTR_CHECK appraise_algos=sha256,sha384,sha512
+ Example of measure and appraise rules allowing fs-verity
+ signed digests on a particular filesystem identified by
+ it's fsuuid:
+
+ measure func=BPRM_CHECK digest_type=hash|verity \
+ fsuuid=... template=ima-sig
+ appraise func=BPRM_CHECK digest_type=hash|verity \
+ fsuuid=...
+
+
Example of measure rule allowing fs-verity's digests on a
particular filesystem with indication of type of digest.
diff --git a/Documentation/security/IMA-templates.rst b/Documentation/security/IMA-templates.rst
index 5e31513e8ec4..390936810ebc 100644
--- a/Documentation/security/IMA-templates.rst
+++ b/Documentation/security/IMA-templates.rst
@@ -71,8 +71,8 @@ descriptors by adding their identifier to the format string
- 'd-modsig': the digest of the event without the appended modsig;
- 'd-type': the type of file digest (e.g. hash, verity[1]);
- 'n-ng': the name of the event, without size limitations;
- - 'sig': the file signature, or the EVM portable signature if the file
- signature is not found;
+ - 'sig': the file signature, based on either the file's/fsverity's digest[1],
+ or the EVM portable signature if the file signature is not found;
- 'modsig' the appended file signature;
- 'buf': the buffer data that was used to generate the hash without size limitations;
- 'evmsig': the EVM portable signature;
diff --git a/security/integrity/ima/ima_appraise.c b/security/integrity/ima/ima_appraise.c
index 7bc180bd808e..68376c56feff 100644
--- a/security/integrity/ima/ima_appraise.c
+++ b/security/integrity/ima/ima_appraise.c
@@ -13,7 +13,9 @@
#include <linux/magic.h>
#include <linux/ima.h>
#include <linux/evm.h>
+#include <linux/fsverity.h>
#include <keys/system_keyring.h>
+#include <uapi/linux/fsverity.h>
#include "ima.h"
@@ -183,13 +185,18 @@ enum hash_algo ima_get_hash_algo(const struct evm_ima_xattr_data *xattr_value,
return ima_hash_algo;
switch (xattr_value->type) {
+ case IMA_VERITY_DIGSIG:
+ sig = (typeof(sig))xattr_value;
+ if (sig->version != 3 || xattr_len <= sizeof(*sig) ||
+ sig->hash_algo >= HASH_ALGO__LAST)
+ return ima_hash_algo;
+ return sig->hash_algo;
case EVM_IMA_XATTR_DIGSIG:
sig = (typeof(sig))xattr_value;
if (sig->version != 2 || xattr_len <= sizeof(*sig)
|| sig->hash_algo >= HASH_ALGO__LAST)
return ima_hash_algo;
return sig->hash_algo;
- break;
case IMA_XATTR_DIGEST_NG:
/* first byte contains algorithm id */
ret = xattr_value->data[0];
@@ -235,15 +242,22 @@ int ima_read_xattr(struct dentry *dentry,
* IMA signature version 3 disambiguates the data that is signed by
* indirectly signing the hash of the ima_file_id structure data.
*
+ * Signing the ima_file_id struct is currently only supported for
+ * IMA_VERITY_DIGSIG type xattrs.
+ *
* Return 0 on success, error code otherwise.
*/
static int calc_file_id_hash(enum evm_ima_xattr_type type,
enum hash_algo algo, const u8 *digest,
struct ima_max_digest_data *hash)
{
- struct ima_file_id file_id = {.hash_algorithm = algo};
+ struct ima_file_id file_id = {
+ .hash_type = IMA_VERITY_DIGSIG, .hash_algorithm = algo};
uint unused = HASH_MAX_DIGESTSIZE - hash_digest_size[algo];
+ if (type != IMA_VERITY_DIGSIG)
+ return -EINVAL;
+
memcpy(file_id.hash, digest, hash_digest_size[algo]);
hash->algo = algo;
@@ -264,6 +278,7 @@ static int xattr_verify(enum ima_hooks func, struct integrity_iint_cache *iint,
struct evm_ima_xattr_data *xattr_value, int xattr_len,
enum integrity_status *status, const char **cause)
{
+ struct ima_max_digest_data hash;
struct signature_v2_hdr *sig;
int rc = -EINVAL, hash_start = 0;
@@ -332,6 +347,36 @@ static int xattr_verify(enum ima_hooks func, struct integrity_iint_cache *iint,
} else {
*status = INTEGRITY_PASS;
}
+ break;
+ case IMA_VERITY_DIGSIG:
+ set_bit(IMA_DIGSIG, &iint->atomic_flags);
+
+ sig = (typeof(sig))xattr_value;
+ if (sig->version != 3) {
+ *cause = "invalid-verity-version";
+ *status = INTEGRITY_FAIL;
+ break;
+ }
+
+ rc = calc_file_id_hash(IMA_VERITY_DIGSIG, iint->ima_hash->algo,
+ iint->ima_hash->digest, &hash);
+ if (rc) {
+ *cause = "verity-hashing-error";
+ *status = INTEGRITY_FAIL;
+ break;
+ }
+
+ rc = integrity_digsig_verify(INTEGRITY_KEYRING_IMA,
+ (const char *)xattr_value,
+ xattr_len, hash.digest,
+ hash.length);
+ if (rc) {
+ *cause = "invalid-verity-signature";
+ *status = INTEGRITY_FAIL;
+ } else {
+ *status = INTEGRITY_PASS;
+ }
+
break;
default:
*status = INTEGRITY_UNKNOWN;
diff --git a/security/integrity/ima/ima_template_lib.c b/security/integrity/ima/ima_template_lib.c
index 44e57d7e5fed..0d4bbb4da59a 100644
--- a/security/integrity/ima/ima_template_lib.c
+++ b/security/integrity/ima/ima_template_lib.c
@@ -499,7 +499,8 @@ int ima_eventsig_init(struct ima_event_data *event_data,
{
struct evm_ima_xattr_data *xattr_value = event_data->xattr_value;
- if ((!xattr_value) || (xattr_value->type != EVM_IMA_XATTR_DIGSIG))
+ if (!xattr_value ||
+ !(xattr_value->type & (EVM_IMA_XATTR_DIGSIG | IMA_VERITY_DIGSIG)))
return ima_eventevmsig_init(event_data, field_data);
return ima_write_template_field_data(xattr_value, event_data->xattr_len,
diff --git a/security/integrity/integrity.h b/security/integrity/integrity.h
index ed4966d943e9..5b1aa8b7d61c 100644
--- a/security/integrity/integrity.h
+++ b/security/integrity/integrity.h
@@ -80,6 +80,7 @@ enum evm_ima_xattr_type {
EVM_IMA_XATTR_DIGSIG,
IMA_XATTR_DIGEST_NG,
EVM_XATTR_PORTABLE_DIGSIG,
+ IMA_VERITY_DIGSIG,
IMA_XATTR_LAST
};
@@ -154,7 +155,9 @@ struct signature_v2_hdr {
/*
* IMA signature version 3 disambiguates the data that is signed, by
- * indirectly signing the hash of the ima_file_id structure data.
+ * indirectly signing the hash of the ima_file_id structure data,
+ * containing either the fsverity_descriptor struct digest or, in the
+ * future, the regular IMA file hash.
*
* (The hash of the ima_file_id structure is only of the portion used.)
*/
--
2.27.0
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