[PATCH v5 7/8] ima: support fs-verity file digest based version 3 signatures
From: Mimi Zohar
Date: Fri Feb 11 2022 - 16:43:56 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.
The policy rule 'appraise_type=' option is extended to support 'sigv3',
which is initiality limited to fs-verity.
The fs-verity 'appraise' rules are identified by the 'digest-type=verity'
option and require the 'appraise_type=sigv3' option. The following
'appraise' policy rule requires fsverity file digests. (The 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 appraise_type=sigv3
Lastly, for IMA to differentiate between the original IMA signature
from an fs-verity signature a new 'xattr_type' named IMA_VERITY_DIGSIG
is defined.
Signed-off-by: Mimi Zohar <zohar@xxxxxxxxxxxxx>
---
Documentation/ABI/testing/ima_policy | 28 ++++++--
Documentation/security/IMA-templates.rst | 4 +-
security/integrity/ima/ima_appraise.c | 79 +++++++++++++++++++++--
security/integrity/ima/ima_policy.c | 26 ++++++--
security/integrity/ima/ima_template_lib.c | 3 +-
security/integrity/integrity.h | 5 +-
6 files changed, 127 insertions(+), 18 deletions(-)
diff --git a/Documentation/ABI/testing/ima_policy b/Documentation/ABI/testing/ima_policy
index ff3c906738cb..508053b8dd0a 100644
--- a/Documentation/ABI/testing/ima_policy
+++ b/Documentation/ABI/testing/ima_policy
@@ -47,7 +47,7 @@ Description:
fgroup:= decimal value
lsm: are LSM specific
option:
- appraise_type:= [imasig] [imasig|modsig]
+ appraise_type:= [imasig] | [imasig|modsig] | [sigv3]
appraise_flag:= [check_blacklist]
Currently, blacklist check is only for files signed with appended
signature.
@@ -153,9 +153,27 @@ Description:
appraise func=SETXATTR_CHECK appraise_algos=sha256,sha384,sha512
- Example of 'measure' rule requiring fs-verity's digests on a
- particular filesystem with indication of type of digest in
- the measurement list.
+ Example of a 'measure' rule requiring fs-verity's digests
+ with indication of type of digest in the measurement list.
measure func=FILE_CHECK digest_type=verity \
- fsuuid=... template=ima-ngv2
+ template=ima-ngv2
+
+ Example of 'measure' and 'appraise' rules requiring fs-verity
+ signatures (version 3) stored in security.ima xattr.
+
+ The 'measure' rule specifies the 'ima-sig' template option,
+ which includes the file signature in the measurement list.
+
+ measure func=BPRM_CHECK digest_type=verity \
+ template=ima-sig
+
+ The 'appraise' rule specifies the type and signature version
+ (sigv3) required.
+
+ appraise func=BPRM_CHECK digest_type=verity \
+ appraise_type=sigv3
+
+ All of these policy rules could, for example, be constrained
+ either based on a filesystem's UUID (fsuuid) or based on LSM
+ labels.
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 c2b429c141a7..71e27dba01ab 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_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;
@@ -263,6 +277,7 @@ 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;
@@ -274,7 +289,10 @@ 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;
}
@@ -303,6 +321,12 @@ 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";
@@ -331,6 +355,44 @@ 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.hdr);
+ 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.hdr.length);
+ if (rc) {
+ *cause = "invalid-verity-signature";
+ *status = INTEGRITY_FAIL;
+ } else {
+ *status = INTEGRITY_PASS;
+ }
+
break;
default:
*status = INTEGRITY_UNKNOWN;
@@ -431,8 +493,15 @@ 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..d3006cc22ab1 100644
--- a/security/integrity/ima/ima_policy.c
+++ b/security/integrity/ima/ima_policy.c
@@ -1311,6 +1311,12 @@ static bool ima_validate_rule(struct ima_rule_entry *entry)
!(entry->flags & IMA_MODSIG_ALLOWED))
return false;
+ /* Ensure APPRAISE verity file implies a v3 signature */
+ if (entry->action == APPRAISE &&
+ (entry->flags & IMA_VERITY_REQUIRED) &&
+ !(entry->flags & IMA_DIGSIG_REQUIRED))
+ return false;
+
return true;
}
@@ -1735,14 +1741,24 @@ static int ima_parse_rule(char *rule, struct ima_rule_entry *entry)
break;
case Opt_appraise_type:
ima_log_string(ab, "appraise_type", args[0].from);
- if ((strcmp(args[0].from, "imasig")) == 0)
+ if ((strcmp(args[0].from, "imasig")) == 0) {
entry->flags |= IMA_DIGSIG_REQUIRED;
- else if (IS_ENABLED(CONFIG_IMA_APPRAISE_MODSIG) &&
- strcmp(args[0].from, "imasig|modsig") == 0)
+ } else if (strcmp(args[0].from, "sigv3") == 0) {
+ /*
+ * Only fsverity supports sigv3 for now.
+ * No need to define a new flag.
+ */
+ if (entry->flags & IMA_VERITY_REQUIRED)
+ entry->flags |= IMA_DIGSIG_REQUIRED;
+ else
+ result = -EINVAL;
+ } else if (IS_ENABLED(CONFIG_IMA_APPRAISE_MODSIG) &&
+ strcmp(args[0].from, "imasig|modsig") == 0) {
entry->flags |= IMA_DIGSIG_REQUIRED |
IMA_MODSIG_ALLOWED;
- else
+ } else {
result = -EINVAL;
+ }
break;
case Opt_appraise_flag:
ima_log_string(ab, "appraise_flag", args[0].from);
@@ -2186,6 +2202,8 @@ 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 if (entry->flags & IMA_VERITY_REQUIRED)
+ seq_puts(m, "appraise_type=sigv3 ");
else
seq_puts(m, "appraise_type=imasig ");
}
diff --git a/security/integrity/ima/ima_template_lib.c b/security/integrity/ima/ima_template_lib.c
index d370fca04de4..ecbe61c53d40 100644
--- a/security/integrity/ima/ima_template_lib.c
+++ b/security/integrity/ima/ima_template_lib.c
@@ -495,7 +495,8 @@ 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 bd38bd451b19..b3267384c028 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
};
@@ -140,7 +141,9 @@ 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