A key added to the IMA keyring must be signed by a key contained in either the
built-in trusted or secondary trusted keyring. IMA also requires these keys
to be a CA. The only option for an end-user to add their own CA is to compile
it into the kernel themselves or to use the insert-sys-cert. Many end-users
do not want to compile their own kernels. With the insert-sys-cert option,
there are missing upstream changes.
Currently, all Machine Owner Keys (MOK) load into the machine keyring. Add
a new Kconfig option to only allow CA keys into the machine keyring. When
compiled with the new INTEGRITY_MACHINE_KEYRING_CA_ENFORCED Kconfig, non CA
keys will load into the platform keyring instead. This will allow the end-
user to enroll their own CA key into the machine keyring for use with IMA.
These patches are based on Jarkko's linux-tpmdd tree.
git://git.kernel.org/pub/scm/linux/kernel/git/jarkko/linux-tpmdd.git
Eric Snowberg (4):
KEYS: Create static version of public_key_verify_signature
X.509: Parse Basic Constraints for CA
KEYS: CA link restriction
integrity: restrict INTEGRITY_KEYRING_MACHINE to restrict_link_by_ca
certs/system_keyring.c | 9 ++--
crypto/asymmetric_keys/restrict.c | 43 +++++++++++++++++++
crypto/asymmetric_keys/x509_cert_parser.c | 9 ++++
include/crypto/public_key.h | 25 +++++++++++
include/keys/system_keyring.h | 3 +-
security/integrity/Kconfig | 21 +++++++++
security/integrity/Makefile | 1 +
security/integrity/digsig.c | 14 ++++--
security/integrity/integrity.h | 3 +-
.../platform_certs/keyring_handler.c | 4 +-
10 files changed, 123 insertions(+), 9 deletions(-)
base-commit: c9e54f38976a1c0ec69c0a6208b3fd55fceb01d1
--
2.27.0
Add a new link restriction. Restrict the addition of keys in a keyring
based on the key to be added being a CA.
Signed-off-by: Eric Snowberg <[email protected]>
---
crypto/asymmetric_keys/restrict.c | 43 +++++++++++++++++++++++++++++++
include/crypto/public_key.h | 15 +++++++++++
2 files changed, 58 insertions(+)
diff --git a/crypto/asymmetric_keys/restrict.c b/crypto/asymmetric_keys/restrict.c
index 6b1ac5f5896a..49bb2ea7f609 100644
--- a/crypto/asymmetric_keys/restrict.c
+++ b/crypto/asymmetric_keys/restrict.c
@@ -108,6 +108,49 @@ int restrict_link_by_signature(struct key *dest_keyring,
return ret;
}
+/**
+ * restrict_link_by_ca - Restrict additions to a ring of CA keys
+ * @dest_keyring: Keyring being linked to.
+ * @type: The type of key being added.
+ * @payload: The payload of the new key.
+ * @trust_keyring: Unused.
+ *
+ * Check if the new certificate is a CA. If it is a CA, then mark the new
+ * certificate as being ok to link.
+ *
+ * Returns 0 if the new certificate was accepted, -ENOKEY if the
+ * certificate is not a CA. -ENOPKG if the signature uses unsupported
+ * crypto, or some other error if there is a matching certificate but
+ * the signature check cannot be performed.
+ */
+int restrict_link_by_ca(struct key *dest_keyring,
+ const struct key_type *type,
+ const union key_payload *payload,
+ struct key *trust_keyring)
+{
+ const struct public_key_signature *sig;
+ const struct public_key *pkey;
+
+ if (type != &key_type_asymmetric)
+ return -EOPNOTSUPP;
+
+ sig = payload->data[asym_auth];
+ if (!sig)
+ return -ENOPKG;
+
+ if (!sig->auth_ids[0] && !sig->auth_ids[1])
+ return -ENOKEY;
+
+ pkey = payload->data[asym_crypto];
+ if (!pkey)
+ return -ENOPKG;
+
+ if (!pkey->key_is_ca)
+ return -ENOKEY;
+
+ return public_key_verify_signature(pkey, sig);
+}
+
static bool match_either_id(const struct asymmetric_key_id **pair,
const struct asymmetric_key_id *single)
{
diff --git a/include/crypto/public_key.h b/include/crypto/public_key.h
index 0521241764b7..5eadb182a400 100644
--- a/include/crypto/public_key.h
+++ b/include/crypto/public_key.h
@@ -72,6 +72,21 @@ extern int restrict_link_by_key_or_keyring_chain(struct key *trust_keyring,
const union key_payload *payload,
struct key *trusted);
+#if IS_REACHABLE(CONFIG_ASYMMETRIC_KEY_TYPE)
+extern int restrict_link_by_ca(struct key *dest_keyring,
+ const struct key_type *type,
+ const union key_payload *payload,
+ struct key *trust_keyring);
+#else
+static inline int restrict_link_by_ca(struct key *dest_keyring,
+ const struct key_type *type,
+ const union key_payload *payload,
+ struct key *trust_keyring)
+{
+ return 0;
+}
+#endif
+
extern int query_asymmetric_key(const struct kernel_pkey_params *,
struct kernel_pkey_query *);
--
2.27.0
Parse the X.509 Basic Constraints. The basic constraints extension
identifies whether the subject of the certificate is a CA.
BasicConstraints ::= SEQUENCE {
cA BOOLEAN DEFAULT FALSE,
pathLenConstraint INTEGER (0..MAX) OPTIONAL }
If the CA is true, store it in a new public_key field call key_is_ca.
This will be used in a follow on patch that requires knowing if the
public key is a CA.
Signed-off-by: Eric Snowberg <[email protected]>
---
crypto/asymmetric_keys/x509_cert_parser.c | 9 +++++++++
include/crypto/public_key.h | 1 +
2 files changed, 10 insertions(+)
diff --git a/crypto/asymmetric_keys/x509_cert_parser.c b/crypto/asymmetric_keys/x509_cert_parser.c
index 2899ed80bb18..38c907f4ce27 100644
--- a/crypto/asymmetric_keys/x509_cert_parser.c
+++ b/crypto/asymmetric_keys/x509_cert_parser.c
@@ -583,6 +583,15 @@ int x509_process_extension(void *context, size_t hdrlen,
return 0;
}
+ if (ctx->last_oid == OID_basicConstraints) {
+ if (v[0] != (ASN1_CONS_BIT | ASN1_SEQ))
+ return -EBADMSG;
+ if (v[1] != vlen - 2)
+ return -EBADMSG;
+ if (v[1] != 0 && v[2] == ASN1_BOOL && v[3] == 1)
+ ctx->cert->pub->key_is_ca = true;
+ }
+
return 0;
}
diff --git a/include/crypto/public_key.h b/include/crypto/public_key.h
index 6d61695e1cde..0521241764b7 100644
--- a/include/crypto/public_key.h
+++ b/include/crypto/public_key.h
@@ -26,6 +26,7 @@ struct public_key {
void *params;
u32 paramlen;
bool key_is_private;
+ bool key_is_ca;
const char *id_type;
const char *pkey_algo;
};
--
2.27.0
On 3/1/22 12:36, Eric Snowberg wrote:
> Add a new link restriction. Restrict the addition of keys in a keyring
> based on the key to be added being a CA.
>
> Signed-off-by: Eric Snowberg <[email protected]>
> ---
> crypto/asymmetric_keys/restrict.c | 43 +++++++++++++++++++++++++++++++
> include/crypto/public_key.h | 15 +++++++++++
> 2 files changed, 58 insertions(+)
>
> diff --git a/crypto/asymmetric_keys/restrict.c b/crypto/asymmetric_keys/restrict.c
> index 6b1ac5f5896a..49bb2ea7f609 100644
> --- a/crypto/asymmetric_keys/restrict.c
> +++ b/crypto/asymmetric_keys/restrict.c
> @@ -108,6 +108,49 @@ int restrict_link_by_signature(struct key *dest_keyring,
> return ret;
> }
>
> +/**
> + * restrict_link_by_ca - Restrict additions to a ring of CA keys
> + * @dest_keyring: Keyring being linked to.
> + * @type: The type of key being added.
> + * @payload: The payload of the new key.
> + * @trust_keyring: Unused.
> + *
> + * Check if the new certificate is a CA. If it is a CA, then mark the new
> + * certificate as being ok to link.
CA = root CA here, right?
> + *
> + * Returns 0 if the new certificate was accepted, -ENOKEY if the
> + * certificate is not a CA. -ENOPKG if the signature uses unsupported
> + * crypto, or some other error if there is a matching certificate but
> + * the signature check cannot be performed.
> + */
> +int restrict_link_by_ca(struct key *dest_keyring,
> + const struct key_type *type,
> + const union key_payload *payload,
> + struct key *trust_keyring)
This function needs to correspond to the key_restrict_link_func_t and
therefore has 4 parameter. Call the unused 'trust_keyring' 'unused' instead?
> +{
> + const struct public_key_signature *sig;
> + const struct public_key *pkey;
> +
> + if (type != &key_type_asymmetric)
> + return -EOPNOTSUPP;
> +
> + sig = payload->data[asym_auth];
> + if (!sig)
> + return -ENOPKG;
> +
> + if (!sig->auth_ids[0] && !sig->auth_ids[1])
> + return -ENOKEY;
> +
> + pkey = payload->data[asym_crypto];
> + if (!pkey)
> + return -ENOPKG;
> +
> + if (!pkey->key_is_ca)
> + return -ENOKEY;
> +
> + return public_key_verify_signature(pkey, sig);
> +}
> +
Comparing this to 'restrict_link_by_signature'... looks good.
> static bool match_either_id(const struct asymmetric_key_id **pair,
> const struct asymmetric_key_id *single)
> {
> diff --git a/include/crypto/public_key.h b/include/crypto/public_key.h
> index 0521241764b7..5eadb182a400 100644
> --- a/include/crypto/public_key.h
> +++ b/include/crypto/public_key.h
> @@ -72,6 +72,21 @@ extern int restrict_link_by_key_or_keyring_chain(struct key *trust_keyring,
> const union key_payload *payload,
> struct key *trusted);
>
> +#if IS_REACHABLE(CONFIG_ASYMMETRIC_KEY_TYPE)
> +extern int restrict_link_by_ca(struct key *dest_keyring,
> + const struct key_type *type,
> + const union key_payload *payload,
> + struct key *trust_keyring);
> +#else
> +static inline int restrict_link_by_ca(struct key *dest_keyring,
> + const struct key_type *type,
> + const union key_payload *payload,
> + struct key *trust_keyring)
> +{
> + return 0;
> +}
> +#endif
> +
> extern int query_asymmetric_key(const struct kernel_pkey_params *,
> struct kernel_pkey_query *);
>
> On Mar 4, 2022, at 8:28 AM, Stefan Berger <[email protected]> wrote:
>
>
> On 3/1/22 12:36, Eric Snowberg wrote:
>> Add a new link restriction. Restrict the addition of keys in a keyring
>> based on the key to be added being a CA.
>>
>> Signed-off-by: Eric Snowberg <[email protected]>
>> ---
>> crypto/asymmetric_keys/restrict.c | 43 +++++++++++++++++++++++++++++++
>> include/crypto/public_key.h | 15 +++++++++++
>> 2 files changed, 58 insertions(+)
>>
>> diff --git a/crypto/asymmetric_keys/restrict.c b/crypto/asymmetric_keys/restrict.c
>> index 6b1ac5f5896a..49bb2ea7f609 100644
>> --- a/crypto/asymmetric_keys/restrict.c
>> +++ b/crypto/asymmetric_keys/restrict.c
>> @@ -108,6 +108,49 @@ int restrict_link_by_signature(struct key *dest_keyring,
>> return ret;
>> }
>> +/**
>> + * restrict_link_by_ca - Restrict additions to a ring of CA keys
>> + * @dest_keyring: Keyring being linked to.
>> + * @type: The type of key being added.
>> + * @payload: The payload of the new key.
>> + * @trust_keyring: Unused.
>> + *
>> + * Check if the new certificate is a CA. If it is a CA, then mark the new
>> + * certificate as being ok to link.
>
> CA = root CA here, right?
Yes, I’ll update the comment
>> + *
>> + * Returns 0 if the new certificate was accepted, -ENOKEY if the
>> + * certificate is not a CA. -ENOPKG if the signature uses unsupported
>> + * crypto, or some other error if there is a matching certificate but
>> + * the signature check cannot be performed.
>> + */
>> +int restrict_link_by_ca(struct key *dest_keyring,
>> + const struct key_type *type,
>> + const union key_payload *payload,
>> + struct key *trust_keyring)
> This function needs to correspond to the key_restrict_link_func_t and therefore has 4 parameter. Call the unused 'trust_keyring' 'unused' instead?
and I’ll change the name in the next round.
> On Mar 4, 2022, at 8:10 AM, Stefan Berger <[email protected]> wrote:
>
>
> On 3/1/22 12:36, Eric Snowberg wrote:
>> Parse the X.509 Basic Constraints. The basic constraints extension
>> identifies whether the subject of the certificate is a CA.
>>
>> BasicConstraints ::= SEQUENCE {
>> cA BOOLEAN DEFAULT FALSE,
>> pathLenConstraint INTEGER (0..MAX) OPTIONAL }
>>
>> If the CA is true, store it in a new public_key field call key_is_ca.
>> This will be used in a follow on patch that requires knowing if the
>> public key is a CA.
>>
>> Signed-off-by: Eric Snowberg <[email protected]>
>> ---
>> crypto/asymmetric_keys/x509_cert_parser.c | 9 +++++++++
>> include/crypto/public_key.h | 1 +
>> 2 files changed, 10 insertions(+)
>>
>> diff --git a/crypto/asymmetric_keys/x509_cert_parser.c b/crypto/asymmetric_keys/x509_cert_parser.c
>> index 2899ed80bb18..38c907f4ce27 100644
>> --- a/crypto/asymmetric_keys/x509_cert_parser.c
>> +++ b/crypto/asymmetric_keys/x509_cert_parser.c
>> @@ -583,6 +583,15 @@ int x509_process_extension(void *context, size_t hdrlen,
>> return 0;
>> }
>> + if (ctx->last_oid == OID_basicConstraints) {
>
> Don't you have to check whether you can access v[0] and v[1]?
Good catch, I’ll add the check
> if (vlen < 3)
>
> return -EBADMSG;
I think this would be best
> or should it even be
>
> if (vlen != 3)
>
> return -EBADMSG;
since the length could be larger than 3 if the optional pathLenConstraint
is supplied.
> On Mar 7, 2022, at 4:01 PM, Mimi Zohar <[email protected]> wrote:
>
> On Mon, 2022-03-07 at 18:06 +0000, Eric Snowberg wrote:
>>
>>>> diff --git a/crypto/asymmetric_keys/restrict.c b/crypto/asymmetric_keys/restrict.c
>>>> index 6b1ac5f5896a..49bb2ea7f609 100644
>>>> --- a/crypto/asymmetric_keys/restrict.c
>>>> +++ b/crypto/asymmetric_keys/restrict.c
>>>> @@ -108,6 +108,49 @@ int restrict_link_by_signature(struct key *dest_keyring,
>>>> return ret;
>>>> }
>>>> +/**
>>>> + * restrict_link_by_ca - Restrict additions to a ring of CA keys
>>>> + * @dest_keyring: Keyring being linked to.
>>>> + * @type: The type of key being added.
>>>> + * @payload: The payload of the new key.
>>>> + * @trust_keyring: Unused.
>>>> + *
>>>> + * Check if the new certificate is a CA. If it is a CA, then mark the new
>>>> + * certificate as being ok to link.
>>>
>>> CA = root CA here, right?
>>
>> Yes, I’ll update the comment
>
> Updating the comment is not enough. There's an existing function named
> "x509_check_for_self_signed()" which determines whether the certificate
> is self-signed.
Originally I tried using that function. However when the restrict link code is called,
all the necessary x509 information is no longer available. The code in
restrict_link_by_ca is basically doing the equivalent to x509_check_for_self_signed.
After verifying the cert has the CA flag set, the call to public_key_verify_signature
validates the cert is self signed.
On 3/9/22 12:12, Stefan Berger wrote:
>
>
> On 3/8/22 13:02, Eric Snowberg wrote:
>>
>>
>>> On Mar 8, 2022, at 5:45 AM, Mimi Zohar <[email protected]> wrote:
>>>
>>> On Mon, 2022-03-07 at 21:31 -0500, Stefan Berger wrote:
>>>>
>>>> On 3/7/22 18:38, Eric Snowberg wrote:
>>>>>
>>>>>
>>>>>> On Mar 7, 2022, at 4:01 PM, Mimi Zohar <[email protected]> wrote:
>>>>>>
>>>>>> On Mon, 2022-03-07 at 18:06 +0000, Eric Snowberg wrote:
>>>>>>>
>>>>>>>>> diff --git a/crypto/asymmetric_keys/restrict.c
>>>>>>>>> b/crypto/asymmetric_keys/restrict.c
>>>>>>>>> index 6b1ac5f5896a..49bb2ea7f609 100644
>>>>>>>>> --- a/crypto/asymmetric_keys/restrict.c
>>>>>>>>> +++ b/crypto/asymmetric_keys/restrict.c
>>>>>>>>> @@ -108,6 +108,49 @@ int restrict_link_by_signature(struct key
>>>>>>>>> *dest_keyring,
>>>>>>>>> return ret;
>>>>>>>>> }
>>>>>>>>> +/**
>>>>>>>>> + * restrict_link_by_ca - Restrict additions to a ring of CA keys
>>>>>>>>> + * @dest_keyring: Keyring being linked to.
>>>>>>>>> + * @type: The type of key being added.
>>>>>>>>> + * @payload: The payload of the new key.
>>>>>>>>> + * @trust_keyring: Unused.
>>>>>>>>> + *
>>>>>>>>> + * Check if the new certificate is a CA. If it is a CA, then
>>>>>>>>> mark the new
>>>>>>>>> + * certificate as being ok to link.
>>>>>>>>
>>>>>>>> CA = root CA here, right?
>>>>>>>
>>>>>>> Yes, I’ll update the comment
>>>>>>
>>>>>> Updating the comment is not enough. There's an existing function
>>>>>> named
>>>>>> "x509_check_for_self_signed()" which determines whether the
>>>>>> certificate
>>>>>> is self-signed.
>>>>>
>>>>> Originally I tried using that function. However when the restrict
>>>>> link code is called,
>>>>> all the necessary x509 information is no longer available. The
>>>>> code in
>>>>> restrict_link_by_ca is basically doing the equivalent to
>>>>> x509_check_for_self_signed.
>>>>> After verifying the cert has the CA flag set, the call to
>>>>> public_key_verify_signature
>>>>> validates the cert is self signed.
>>>>>
>>>> Isn't x509_cert_parse() being called as part of parsing the
>>>> certificate?
>>>> If so, it seems to check for a self-signed certificate every time. You
>>>> could add something like the following to
>>>> x509_check_for_self_signed(cert):
>>>> pub->x509_self_signed = cert->self_signed = true;
>>>>
>>>> This could then reduce the function in 3/4 to something like:
>>>>
>>>> return payload->data[asym_crypto]->x509_self_signed;
>>
>> When I was studying the restriction code, before writing this patch,
>> it looked like
>> it was written from the standpoint to be as generic as possible. All
>> code contained
>> within it works on either a public_key_signature or a public_key. I
>> had assumed it
>> was written this way to be used with different asymmetrical key types
>> now and in
>> the future. I called the public_key_verify_signature function instead
>> of interrogating
>> the x509 payload to keep in line with what I thought was the original
>> design. Let me
>> know if I should be carrying x509 code in here to make the change above.
>
> It does not seem right if there were two functions trying to determine
> whether an x509 cert is self-signed. The existing is invoked as part of
> loading a key onto the machine keyring from what I can see. It has
> access to more data about the cert and therefore can do stronger tests,
> yours doesn't have access to the data. So I guess I would remember in a
> boolean in the public key structure that the x509 cert it comes from was
> self signed following the existing test. Key in your function may be
> that that payload->data[] array is guaranteed to be from the x509 cert
> as set in x509_key_preparse().
>
> https://elixir.bootlin.com/linux/v5.17-rc7/source/crypto/asymmetric_keys/x509_public_key.c#L236
>
>
> Stefan
Sorry for the mess in the response. The first version is the good one :-)
On Tue, 2022-03-08 at 18:02 +0000, Eric Snowberg wrote:
> > On Mar 8, 2022, at 5:45 AM, Mimi Zohar <[email protected]> wrote:
> > Agreed, as long as the other two criteria are also met: CA and keyUsage
> > should be required and limited to keyCertSign.
>
> I have added the key_is_ca in the public_key header. I can look at adding the usage
> too. Before doing this I would like to understand the "limited to" above. Many CA keys
> that have keyCertSign set, also have digitalSignature set for key usage. For
> example:
>
> http://cacerts.digicert.com/DigiCertEVCodeSigningCA-SHA2.crt
>
> Are you saying we would want to exclude a CA like the one above, since it as the
> digitalSignature usage set too?
Yes, the "machine" keyring is defining a new root of trust to support
allowing end-users the ability "to add their own keys and sign modules
they trust". There should be a clear distinction between keys used
for certificate signing from those used for code signing. Certificate
signing keys should be added to the .machine keyring. Code signing
keys should be added to the IMA keyring.
thanks,
Mimi
On 3/9/22 13:13, Eric Snowberg wrote:
>
>
>> On Mar 9, 2022, at 10:12 AM, Stefan Berger <[email protected]> wrote:
>>
>>
>>
>> On 3/8/22 13:02, Eric Snowberg wrote:
>>>> On Mar 8, 2022, at 5:45 AM, Mimi Zohar <[email protected]> wrote:
>>>>
>>>> On Mon, 2022-03-07 at 21:31 -0500, Stefan Berger wrote:
>>>>>
>>>>> On 3/7/22 18:38, Eric Snowberg wrote:
>>>>>>
>>>>>>
>>>>>>> On Mar 7, 2022, at 4:01 PM, Mimi Zohar <[email protected]> wrote:
>>>>>>>
>>>>>>> On Mon, 2022-03-07 at 18:06 +0000, Eric Snowberg wrote:
>>>>>>>>
>>>>>>>>>> diff --git a/crypto/asymmetric_keys/restrict.c b/crypto/asymmetric_keys/restrict.c
>>>>>>>>>> index 6b1ac5f5896a..49bb2ea7f609 100644
>>>>>>>>>> --- a/crypto/asymmetric_keys/restrict.c
>>>>>>>>>> +++ b/crypto/asymmetric_keys/restrict.c
>>>>>>>>>> @@ -108,6 +108,49 @@ int restrict_link_by_signature(struct key *dest_keyring,
>>>>>>>>>> return ret;
>>>>>>>>>> }
>>>>>>>>>> +/**
>>>>>>>>>> + * restrict_link_by_ca - Restrict additions to a ring of CA keys
>>>>>>>>>> + * @dest_keyring: Keyring being linked to.
>>>>>>>>>> + * @type: The type of key being added.
>>>>>>>>>> + * @payload: The payload of the new key.
>>>>>>>>>> + * @trust_keyring: Unused.
>>>>>>>>>> + *
>>>>>>>>>> + * Check if the new certificate is a CA. If it is a CA, then mark the new
>>>>>>>>>> + * certificate as being ok to link.
>>>>>>>>>
>>>>>>>>> CA = root CA here, right?
>>>>>>>>
>>>>>>>> Yes, I’ll update the comment
>>>>>>>
>>>>>>> Updating the comment is not enough. There's an existing function named
>>>>>>> "x509_check_for_self_signed()" which determines whether the certificate
>>>>>>> is self-signed.
>>>>>>
>>>>>> Originally I tried using that function. However when the restrict link code is called,
>>>>>> all the necessary x509 information is no longer available. The code in
>>>>>> restrict_link_by_ca is basically doing the equivalent to x509_check_for_self_signed.
>>>>>> After verifying the cert has the CA flag set, the call to public_key_verify_signature
>>>>>> validates the cert is self signed.
>>>>>>
>>>>> Isn't x509_cert_parse() being called as part of parsing the certificate?
>>>>> If so, it seems to check for a self-signed certificate every time. You
>>>>> could add something like the following to x509_check_for_self_signed(cert):
>>>>> pub->x509_self_signed = cert->self_signed = true;
>>>>>
>>>>> This could then reduce the function in 3/4 to something like:
>>>>>
>>>>> return payload->data[asym_crypto]->x509_self_signed;
>>> When I was studying the restriction code, before writing this patch, it looked like
>>> it was written from the standpoint to be as generic as possible. All code contained
>>> within it works on either a public_key_signature or a public_key. I had assumed it
>>> was written this way to be used with different asymmetrical key types now and in
>>> the future. I called the public_key_verify_signature function instead of interrogating
>>> the x509 payload to keep in line with what I thought was the original design. Let me
>>> know if I should be carrying x509 code in here to make the change above.
>>
>> It does not seem right if there were two functions trying to determine whether an x509 cert is self-signed. The existing is invoked as part of loading a key onto the machine keyring from what I can see. It has access to more data about the cert and therefore can do stronger tests, yours doesn't have access to the data. So I guess I would remember in a boolean in the public key structure that the x509 cert it comes from was self signed following the existing test. Key in your function may be that that payload->data[] array is guaranteed to be from the x509 cert as set in x509_key_preparse().
>>
>> https://elixir.bootlin.com/linux/v5.17-rc7/source/crypto/asymmetric_keys/x509_public_key.c#L236
>
> I could add another bool to the public key structure to designate if the key was self signed,
> but this seems to go against what the kernel document states. "Asymmetric / Public-key
> Cryptography Key Type” [1] states:
>
> "The “asymmetric” key type is designed to be a container for the keys used in public-key
> cryptography, without imposing any particular restrictions on the form or mechanism of
> the cryptography or form of the key.
>
> The asymmetric key is given a subtype that defines what sort of data is associated with
> the key and provides operations to describe and destroy it. However, no requirement is
> made that the key data actually be stored in the key."
>
> Now every public key type would need to fill in the information on whether the key is self
> signed or not. Instead of going through the public_key_verify_signature function currently
> used in this patch.
Every public key extracted from a x509 certificate would have to set
this field to true if the public key originates from a self-signed x509
cert. Is this different from this code here where now every public key
would have to set the key_is_ca field?
+ if (v[1] != 0 && v[2] == ASN1_BOOL && v[3] == 1)
+ ctx->cert->pub->key_is_ca = true;
The extension I would have suggested looked similar:
cert->pub->x509_self_sign = cert->self_signed = true
[ to be put here:
https://elixir.bootlin.com/linux/v5.17-rc7/source/crypto/asymmetric_keys/x509_public_key.c#L147
]
>
> https://docs.kernel.org/crypto/asymmetric-keys.html
>
On 3/11/22 15:23, Stefan Berger wrote:
>
>
> On 3/11/22 13:44, Eric Snowberg wrote:
>>
>>
>>> On Mar 9, 2022, at 12:02 PM, Stefan Berger <[email protected]>
>>> wrote:
>>>
>>>
>>>
>>> On 3/9/22 13:13, Eric Snowberg wrote:
>>>>> On Mar 9, 2022, at 10:12 AM, Stefan Berger <[email protected]>
>>>>> wrote:
>>>>>
>>>>>
>>>>>
>>>>> On 3/8/22 13:02, Eric Snowberg wrote:
>>>>>>> On Mar 8, 2022, at 5:45 AM, Mimi Zohar <[email protected]> wrote:
>>>>>>>
>>>>>>> On Mon, 2022-03-07 at 21:31 -0500, Stefan Berger wrote:
>>>>>>>>
>>>>>>>> On 3/7/22 18:38, Eric Snowberg wrote:
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>> On Mar 7, 2022, at 4:01 PM, Mimi Zohar <[email protected]>
>>>>>>>>>> wrote:
>>>>>>>>>>
>>>>>>>>>> On Mon, 2022-03-07 at 18:06 +0000, Eric Snowberg wrote:
>>>>>>>>>>>
>>>>>>>>>>>>> diff --git a/crypto/asymmetric_keys/restrict.c
>>>>>>>>>>>>> b/crypto/asymmetric_keys/restrict.c
>>>>>>>>>>>>> index 6b1ac5f5896a..49bb2ea7f609 100644
>>>>>>>>>>>>> --- a/crypto/asymmetric_keys/restrict.c
>>>>>>>>>>>>> +++ b/crypto/asymmetric_keys/restrict.c
>>>>>>>>>>>>> @@ -108,6 +108,49 @@ int restrict_link_by_signature(struct
>>>>>>>>>>>>> key *dest_keyring,
>>>>>>>>>>>>> return ret;
>>>>>>>>>>>>> }
>>>>>>>>>>>>> +/**
>>>>>>>>>>>>> + * restrict_link_by_ca - Restrict additions to a ring of
>>>>>>>>>>>>> CA keys
>>>>>>>>>>>>> + * @dest_keyring: Keyring being linked to.
>>>>>>>>>>>>> + * @type: The type of key being added.
>>>>>>>>>>>>> + * @payload: The payload of the new key.
>>>>>>>>>>>>> + * @trust_keyring: Unused.
>>>>>>>>>>>>> + *
>>>>>>>>>>>>> + * Check if the new certificate is a CA. If it is a CA,
>>>>>>>>>>>>> then mark the new
>>>>>>>>>>>>> + * certificate as being ok to link.
>>>>>>>>>>>>
>>>>>>>>>>>> CA = root CA here, right?
>>>>>>>>>>>
>>>>>>>>>>> Yes, I’ll update the comment
>>>>>>>>>>
>>>>>>>>>> Updating the comment is not enough. There's an existing
>>>>>>>>>> function named
>>>>>>>>>> "x509_check_for_self_signed()" which determines whether the
>>>>>>>>>> certificate
>>>>>>>>>> is self-signed.
>>>>>>>>>
>>>>>>>>> Originally I tried using that function. However when the
>>>>>>>>> restrict link code is called,
>>>>>>>>> all the necessary x509 information is no longer available.
>>>>>>>>> The code in
>>>>>>>>> restrict_link_by_ca is basically doing the equivalent to
>>>>>>>>> x509_check_for_self_signed.
>>>>>>>>> After verifying the cert has the CA flag set, the call to
>>>>>>>>> public_key_verify_signature
>>>>>>>>> validates the cert is self signed.
>>>>>>>>>
>>>>>>>> Isn't x509_cert_parse() being called as part of parsing the
>>>>>>>> certificate?
>>>>>>>> If so, it seems to check for a self-signed certificate every
>>>>>>>> time. You
>>>>>>>> could add something like the following to
>>>>>>>> x509_check_for_self_signed(cert):
>>>>>>>> pub->x509_self_signed = cert->self_signed = true;
>>>>>>>>
>>>>>>>> This could then reduce the function in 3/4 to something like:
>>>>>>>>
>>>>>>>> return payload->data[asym_crypto]->x509_self_signed;
>>>>>> When I was studying the restriction code, before writing this
>>>>>> patch, it looked like
>>>>>> it was written from the standpoint to be as generic as possible.
>>>>>> All code contained
>>>>>> within it works on either a public_key_signature or a public_key.
>>>>>> I had assumed it
>>>>>> was written this way to be used with different asymmetrical key
>>>>>> types now and in
>>>>>> the future. I called the public_key_verify_signature function
>>>>>> instead of interrogating
>>>>>> the x509 payload to keep in line with what I thought was the
>>>>>> original design. Let me
>>>>>> know if I should be carrying x509 code in here to make the change
>>>>>> above.
>>>>>
>>>>> It does not seem right if there were two functions trying to
>>>>> determine whether an x509 cert is self-signed. The existing is
>>>>> invoked as part of loading a key onto the machine keyring from what
>>>>> I can see. It has access to more data about the cert and therefore
>>>>> can do stronger tests, yours doesn't have access to the data. So I
>>>>> guess I would remember in a boolean in the public key structure
>>>>> that the x509 cert it comes from was self signed following the
>>>>> existing test. Key in your function may be that that
>>>>> payload->data[] array is guaranteed to be from the x509 cert as set
>>>>> in x509_key_preparse().
>>>>>
>>>>> https://elixir.bootlin.com/linux/v5.17-rc7/source/crypto/asymmetric_keys/x509_public_key.c#L236
>>>>>
>>>> I could add another bool to the public key structure to designate if
>>>> the key was self signed,
>>>> but this seems to go against what the kernel document states.
>>>> "Asymmetric / Public-key
>>>> Cryptography Key Type” [1] states:
>>>> "The “asymmetric” key type is designed to be a container for the
>>>> keys used in public-key
>>>> cryptography, without imposing any particular restrictions on the
>>>> form or mechanism of
>>>> the cryptography or form of the key.
>>>> The asymmetric key is given a subtype that defines what sort of data
>>>> is associated with
>>>> the key and provides operations to describe and destroy it. However,
>>>> no requirement is
>>>> made that the key data actually be stored in the key."
>>>> Now every public key type would need to fill in the information on
>>>> whether the key is self
>>>> signed or not. Instead of going through the
>>>> public_key_verify_signature function currently
>>>> used in this patch.
>>>
>>> Every public key extracted from a x509 certificate would have to set
>>> this field to true if the public key originates from a self-signed
>>> x509 cert. Is this different from this code here where now every
>>> public key would have to set the key_is_ca field?
>>
>> The information to determine if the key is a CA can not be derived
>> without help from
>> the specific key type. Up to this point, no one has needed it.
>>
>>>
>>> + if (v[1] != 0 && v[2] == ASN1_BOOL && v[3] == 1)
>>> + ctx->cert->pub->key_is_ca = true;
>>>
>>> The extension I would have suggested looked similar:
>>>
>>> cert->pub->x509_self_sign = cert->self_signed = true
>>>
>>> [ to be put here:
>>> https://elixir.bootlin.com/linux/v5.17-rc7/source/crypto/asymmetric_keys/x509_public_key.c#L147
>>> ]
>>
>> The information to determine if a key is self signed can be derived
>> without help
>> from the specific key type. This can be achieved without modification
>> to a generic
>> public header file. Adding a field to the public header would need to
>> either be
>> x509 specific or generic for all key types. Adding a x509 specific
>> field seems to
>> go against the goal outlined in the kernel documentation. Adding a
>> generic
>> self_signed field impacts all key types, now each needs to be modified
>> to fill in
>> the new field.
>>
>
> If we now called the generic field cert_self_signed we could let it
> indicate whether the certificate the key was extracted from was
> self-self signed. The next question then is how many different types of
> certificates does the key subsystem support besides x509 so we know
> where to set this field if necessary? I don't know of any other... x509
> seems to be the only type of certificate associated with struct public_key.
> What seems to be the case is that pkcs7 also runs the x509 cert parser
> to extract an x509 certificate, thus the flag will be set down this call
> path as well.
>
> https://elixir.bootlin.com/linux/latest/source/crypto/asymmetric_keys/pkcs7_parser.c#L408
>
>
> Further, the public_key struct is only used in a few places and only in
> the crypto/asymmetric_keys directory filled in. Its usage in pkcs8 seems
> not relevant for certs, so leaving cert_self_signed there uninitialized
> seems just right. The code in public_key.c seems to not deal with
> certificates. So what's left is the x509_cert_parser.c and the function
> x509_cert_parse() allocates it and then calls
> x509_check_for_self_signed(cert), which can set the flag.
>
> It looks to me giving it a generic name and only ever setting it to true
> iin x509_check_for_self_sign(cert) should work.
Otherwise maybe we could introduce
struct cert_info {
bool is_ca;
bool self_sign;
}
And use it like this:
+ if (v[1] != 0 && v[2] == ASN1_BOOL && v[3] == 1)
+ ctx->cert->cert_info->is_ca = true;
New index in the data array:
prep->payload.data[asym_subtype] = &public_key_subtype;
prep->payload.data[asym_key_ids] = kids;
prep->payload.data[asym_crypto] = cert->pub;
prep->payload.data[asym_auth] = cert->sig;
prep->payload.data[asym_cert_info] = cert->cert_info;
There are a few more places where this new array index would need to be
set to NULL.