Re: [PATCH 3/4] KEYS: CA link restriction
From: Stefan Berger
Date: Wed Mar 09 2022 - 12:18:44 EST
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 <zohar@xxxxxxxxxxxxx> 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 <zohar@xxxxxxxxxxxxx> 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 :-)