[PATCH v4 7/8] ima: support fs-verity file digest based version 3 signatures
From: Mimi Zohar
Date: Mon Feb 07 2022 - 20:50:18 EST
Instead of calculating a regular file hash and verifying the signature
stored in the 'security.ima' xattr against the calculated file hash, get
fs-verity's file digest and verify the signature (version 3) stored in
'security.ima' against the digest.
To differentiate between IMA's and fs-verity's signatures, define a
new signature type named 'IMA_VERITY_DIGSIG'.
Update the 'ima-sig' template field to also display the new fs-verity
signature type.
To prevent abuse of the different signature formats, policy rules must be
limited to a specific signature version. The following 'appraise' policy
rule requires fsverity file digests (signature v3). The policy rule may
be constrained, for example based on a fsuuid or LSM label.
Basic fs-verity policy rule example:
appraise func=BPRM_CHECK digest_type=verity
Signed-off-by: Mimi Zohar <zohar@xxxxxxxxxxxxx>
---
Documentation/ABI/testing/ima_policy | 12 ++++
Documentation/security/IMA-templates.rst | 4 +-
security/integrity/ima/ima_appraise.c | 79 +++++++++++++++++++++--
security/integrity/ima/ima_policy.c | 9 ++-
security/integrity/ima/ima_template_lib.c | 3 +-
security/integrity/integrity.h | 5 +-
6 files changed, 100 insertions(+), 12 deletions(-)
diff --git a/Documentation/ABI/testing/ima_policy b/Documentation/ABI/testing/ima_policy
index ff3c906738cb..aabbb206098d 100644
--- a/Documentation/ABI/testing/ima_policy
+++ b/Documentation/ABI/testing/ima_policy
@@ -159,3 +159,15 @@ Description:
measure func=FILE_CHECK digest_type=verity \
fsuuid=... template=ima-ngv2
+
+ Example of 'measure' and 'appraise' rules requiring fs-verity
+ signatures (version 3) stored in security.ima xattr. The
+ 'ima-sig' template option includes the signature in the
+ measurement list. The 'appraise' rule verifies the signature.
+ These policy rules are limited to a particular filesystem
+ based on its fsuuid.
+
+ measure func=BPRM_CHECK digest_type=verity \
+ fsuuid=... template=ima-sig
+ appraise func=BPRM_CHECK digest_type=verity \
+ fsuuid=...
diff --git a/Documentation/security/IMA-templates.rst b/Documentation/security/IMA-templates.rst
index 1e3fe986764e..fe9bc2595fa2 100644
--- a/Documentation/security/IMA-templates.rst
+++ b/Documentation/security/IMA-templates.rst
@@ -72,8 +72,8 @@ descriptors by adding their identifier to the format string
- 'd-type': differentiate between fs-verity's Merkle tree based file hash
from a regular IMA file hash measurement.
- '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..98f2ef99afc0 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;
@@ -275,7 +290,10 @@ static int xattr_verify(enum ima_hooks func, struct integrity_iint_cache *iint,
case IMA_XATTR_DIGEST:
if (*status != INTEGRITY_PASS_IMMUTABLE) {
if (iint->flags & IMA_DIGSIG_REQUIRED) {
- *cause = "IMA-signature-required";
+ if (iint->flags & IMA_VERITY_REQUIRED)
+ *cause = "verity-signature-required";
+ else
+ *cause = "IMA-signature-required";
*status = INTEGRITY_FAIL;
break;
}
@@ -304,6 +322,12 @@ static int xattr_verify(enum ima_hooks func, struct integrity_iint_cache *iint,
case EVM_IMA_XATTR_DIGSIG:
set_bit(IMA_DIGSIG, &iint->atomic_flags);
+ if (iint->flags & (IMA_DIGSIG_REQUIRED | IMA_VERITY_REQUIRED)) {
+ *cause = "verity-signature-required";
+ *status = INTEGRITY_FAIL;
+ break;
+ }
+
sig = (typeof(sig))xattr_value;
if (sig->version != 2) {
*cause = "invalid-signature-version";
@@ -332,6 +356,44 @@ 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);
+
+ if (iint->flags & IMA_DIGSIG_REQUIRED) {
+ if (!(iint->flags & IMA_VERITY_REQUIRED)) {
+ *cause = "IMA-signature-required";
+ *status = INTEGRITY_FAIL;
+ break;
+ }
+ }
+
+ sig = (typeof(sig))xattr_value;
+ if (sig->version != 3) {
+ *cause = "invalid-signature-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 = "sigv3-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;
@@ -432,8 +494,15 @@ int ima_appraise_measurement(enum ima_hooks func,
if (rc && rc != -ENODATA)
goto out;
- cause = iint->flags & IMA_DIGSIG_REQUIRED ?
- "IMA-signature-required" : "missing-hash";
+ if (iint->flags & IMA_DIGSIG_REQUIRED) {
+ if (iint->flags & IMA_VERITY_REQUIRED)
+ cause = "verity-signature-required";
+ else
+ cause = "IMA-signature-required";
+ } else {
+ cause = "missing-hash";
+ }
+
status = INTEGRITY_NOLABEL;
if (file->f_mode & FMODE_CREATED)
iint->flags |= IMA_NEW_FILE;
diff --git a/security/integrity/ima/ima_policy.c b/security/integrity/ima/ima_policy.c
index 28aca1f9633b..576cbe790e27 100644
--- a/security/integrity/ima/ima_policy.c
+++ b/security/integrity/ima/ima_policy.c
@@ -1728,10 +1728,13 @@ static int ima_parse_rule(char *rule, struct ima_rule_entry *entry)
break;
case Opt_digest_type:
ima_log_string(ab, "digest_type", args[0].from);
- if ((strcmp(args[0].from, "verity")) == 0)
+ if ((strcmp(args[0].from, "verity")) == 0) {
entry->flags |= IMA_VERITY_REQUIRED;
- else
+ if (entry->action == APPRAISE)
+ entry->flags |= IMA_DIGSIG_REQUIRED;
+ } else {
result = -EINVAL;
+ }
break;
case Opt_appraise_type:
ima_log_string(ab, "appraise_type", args[0].from);
@@ -2186,7 +2189,7 @@ int ima_policy_show(struct seq_file *m, void *v)
if (entry->flags & IMA_DIGSIG_REQUIRED) {
if (entry->flags & IMA_MODSIG_ALLOWED)
seq_puts(m, "appraise_type=imasig|modsig ");
- else
+ else if (!(entry->flags & IMA_VERITY_REQUIRED))
seq_puts(m, "appraise_type=imasig ");
}
if (entry->flags & IMA_VERITY_REQUIRED)
diff --git a/security/integrity/ima/ima_template_lib.c b/security/integrity/ima/ima_template_lib.c
index 31573b4c7763..8f789ee4383e 100644
--- a/security/integrity/ima/ima_template_lib.c
+++ b/security/integrity/ima/ima_template_lib.c
@@ -498,7 +498,8 @@ 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 f59f83527c0c..df68f291fbf0 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