netdev - Re: [GIT PULL] Keys: Set 4

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Date:   Fri, 16 Aug 2019 14:36:42 +0100
From:   David Howells <dhowells@...hat.com>
To:     Mimi Zohar <zohar@...ux.ibm.com>
Cc:     dhowells@...hat.com,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        James Morris <jmorris@...ei.org>, keyrings@...r.kernel.org,
        Netdev <netdev@...r.kernel.org>, linux-nfs@...r.kernel.org,
        CIFS <linux-cifs@...r.kernel.org>, linux-afs@...ts.infradead.org,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        linux-integrity@...r.kernel.org,
        LSM List <linux-security-module@...r.kernel.org>,
        Linux List Kernel Mailing <linux-kernel@...r.kernel.org>
Subject: Re: [GIT PULL] Keys: Set 4 - Key ACLs for 5.3

Mimi Zohar <zohar@...ux.ibm.com> wrote:

> Sorry for the delay.  An exception is needed for loading builtin keys
> "KEY_ALLOC_BUILT_IN" onto a keyring that is not writable by userspace.
>  The following works, but probably is not how David would handle the
> exception.

I think the attached is the right way to fix it.

load_system_certificate_list(), for example, when it creates keys does this:

	key = key_create_or_update(make_key_ref(builtin_trusted_keys, 1),

marking the keyring as "possessed" in make_key_ref().  This allows the
possessor permits to be used - and that's the *only* way to use them for
internal keyrings like this because you can't link to them and you can't join
them.

David
---
diff --git a/certs/system_keyring.c b/certs/system_keyring.c
index 57be78b5fdfc..1f8f26f7bb05 100644
--- a/certs/system_keyring.c
+++ b/certs/system_keyring.c
@@ -99,7 +99,7 @@ static __init int system_trusted_keyring_init(void)
 	builtin_trusted_keys =
 		keyring_alloc(".builtin_trusted_keys",
 			      KUIDT_INIT(0), KGIDT_INIT(0), current_cred(),
-			      &internal_key_acl, KEY_ALLOC_NOT_IN_QUOTA,
+			      &internal_keyring_acl, KEY_ALLOC_NOT_IN_QUOTA,
 			      NULL, NULL);
 	if (IS_ERR(builtin_trusted_keys))
 		panic("Can't allocate builtin trusted keyring\n");
diff --git a/security/keys/permission.c b/security/keys/permission.c
index fc84d9ef6239..86efd3eaf083 100644
--- a/security/keys/permission.c
+++ b/security/keys/permission.c
@@ -47,7 +47,7 @@ struct key_acl internal_keyring_acl = {
 	.usage	= REFCOUNT_INIT(1),
 	.nr_ace	= 2,
 	.aces = {
-		KEY_POSSESSOR_ACE(KEY_ACE_SEARCH),
+		KEY_POSSESSOR_ACE(KEY_ACE_SEARCH | KEY_ACE_WRITE),
 		KEY_OWNER_ACE(KEY_ACE_VIEW | KEY_ACE_READ | KEY_ACE_SEARCH),
 	}
 };