From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-8.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id A1731C433E1 for ; Thu, 9 Jul 2020 16:28:54 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 80A48207DD for ; Thu, 9 Jul 2020 16:28:54 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726910AbgGIQ2w (ORCPT ); Thu, 9 Jul 2020 12:28:52 -0400 Received: from youngberry.canonical.com ([91.189.89.112]:42153 "EHLO youngberry.canonical.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726408AbgGIQ2w (ORCPT ); Thu, 9 Jul 2020 12:28:52 -0400 Received: from static-50-53-54-182.bvtn.or.frontiernet.net ([50.53.54.182] helo=[192.168.192.153]) by youngberry.canonical.com with esmtpsa (TLS1.2:ECDHE_RSA_AES_128_GCM_SHA256:128) (Exim 4.86_2) (envelope-from ) id 1jtZPh-0004eO-A2; Thu, 09 Jul 2020 16:28:45 +0000 Subject: Re: [PATCH v18 05/23] net: Prepare UDS for security module stacking To: Stephen Smalley , Casey Schaufler Cc: Casey Schaufler , James Morris , LSM List , SElinux list , Kees Cook , Tetsuo Handa , Paul Moore , Stephen Smalley , netdev@vger.kernel.org References: <20200709001234.9719-1-casey@schaufler-ca.com> <20200709001234.9719-6-casey@schaufler-ca.com> From: John Johansen Autocrypt: addr=john.johansen@canonical.com; prefer-encrypt=mutual; keydata= LS0tLS1CRUdJTiBQR1AgUFVCTElDIEtFWSBCTE9DSy0tLS0tCgptUUlOQkU1bXJQb0JFQURB azE5UHNnVmdCS2tJbW1SMmlzUFE2bzdLSmhUVEtqSmR3VmJrV1NuTm4rbzZVcDVrCm5LUDFm 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lsmblob. Update the >> security_socket_getpeersec_dgram() interface to use the >> lsmblob. There is a small amount of scaffolding code >> that will come out when the security_secid_to_secctx() >> code is brought in line with the lsmblob. >> >> The secid field of the unix_skb_parms structure has been >> replaced with a pointer to an lsmblob structure, and the >> lsmblob is allocated as needed. This is similar to how the >> list of passed files is managed. While an lsmblob structure >> will fit in the available space today, there is no guarantee >> that the addition of other data to the unix_skb_parms or >> support for additional security modules wouldn't exceed what >> is available. >> >> Reviewed-by: Kees Cook >> Signed-off-by: Casey Schaufler >> Cc: netdev@vger.kernel.org >> --- > >> diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c >> index 3385a7a0b231..d246aefcf4da 100644 >> --- a/net/unix/af_unix.c >> +++ b/net/unix/af_unix.c >> @@ -138,17 +138,23 @@ static struct hlist_head *unix_sockets_unbound(void *addr) >> #ifdef CONFIG_SECURITY_NETWORK >> static void unix_get_secdata(struct scm_cookie *scm, struct sk_buff *skb) >> { >> - UNIXCB(skb).secid = scm->secid; >> + UNIXCB(skb).lsmdata = kmemdup(&scm->lsmblob, sizeof(scm->lsmblob), >> + GFP_KERNEL); >> } >> >> static inline void unix_set_secdata(struct scm_cookie *scm, struct sk_buff *skb) >> { >> - scm->secid = UNIXCB(skb).secid; >> + if (likely(UNIXCB(skb).lsmdata)) >> + scm->lsmblob = *(UNIXCB(skb).lsmdata); >> + else >> + lsmblob_init(&scm->lsmblob, 0); >> } >> >> static inline bool unix_secdata_eq(struct scm_cookie *scm, struct sk_buff *skb) >> { >> - return (scm->secid == UNIXCB(skb).secid); >> + if (likely(UNIXCB(skb).lsmdata)) >> + return lsmblob_equal(&scm->lsmblob, UNIXCB(skb).lsmdata); >> + return false; >> } > > I don't think that this provides sensible behavior to userspace. On a > transient memory allocation failure, instead of returning an error to > the sender and letting them handle it, this will just proceed with > sending the message without its associated security information, and > potentially split messages on arbitrary boundaries because it cannot > tell whether the sender had the same security information. I think > you instead need to change unix_get_secdata() to return an error on > allocation failure and propagate that up to the sender. Not a fan of > this change in general both due to extra overhead on this code path > and potential for breakage on allocation failures. I know it was > motivated by paul's observation that we won't be able to fit many more > secids into the cb but not sure we have to go there prematurely, > especially absent its usage by upstream AA (no unix_stream_connect > hook implementation upstream). Also not sure how the whole bpf local I'm not sure how premature it is, I am running late for 5.9 but would like to land apparmor unix mediation in 5.10 > storage approach to supporting security modules (or at least bpf lsm) > might reduce need for expanding these structures? >