LKML Archive on
 help / color / Atom feed
From: Casey Schaufler <>
To: Al Viro <>,
	Casey Schaufler <>
Subject: Re: [PATCH] Version 8 (2.6.23) Smack: Simplified Mandatory Access Control Kernel
Date: Thu, 18 Oct 2007 13:13:02 -0700 (PDT)
Message-ID: <> (raw)
In-Reply-To: <>

--- Al Viro <> wrote:

> On Tue, Oct 16, 2007 at 09:17:40PM -0700, Casey Schaufler wrote:
> At random:
> > +static int smack_netlabel(struct sock *sk)
> > +{
> > +	static int initialized;
> > +	struct socket_smack *ssp = sk->sk_security;
> > +	struct netlbl_lsm_secattr secattr;
> > +	int rc = 0;
> > +
> > +	if (!initialized) {
> > +		smk_cipso_doi();
> > +		initialized = 1;
> > +	}
> And just what happens if another task calls the same while we are
> blocked on allocation in smk_cipso_doi()?

I assume that swapping the two lines,

	initialized = 1;

although it looks like it would suffice, isn't really good enough.

> Another problem is your handling of smk_known - you add to head under
> mutex; fine.  However, you read without one _and_ have no barriers
> in initializing new list entries.
> Think what happens if CPU1 adds to list and CPU2 sees write to smk_known
> *before* it sees write to ->smk_next.  We see a single-element list and
> we'll be lucky if that single entry won't be FUBAR.

Help me understand this:

        if (skp == NULL) {
                skp = kzalloc(sizeof(struct smack_known), GFP_KERNEL);
                if (skp != NULL) {
                        skp->smk_next = smack_known;
                        strncpy(skp->smk_known, smack, SMK_MAXLEN);
                        skp->smk_secid = smack_next_secid++;
                        skp->smk_cipso = NULL;
                        smack_known = skp;

CPU1 sets smk_next to smack_known. 
CPU1 fills in the rest of the entry.
CPU1 sets smack_known to skp (the entry).

CPU2 will either see the old value for smack_known,
in which case this entry isn't actually on the list yet,
or it will see the new value in smack_known. Since smk_next
is set before the entry is added to the list, it seems that
the scenario you've outlined shouldn't happen. I assume then
that you're refering to a case where the memory seen by the
two CPUs doesn't match. That still wouldn't account for the
"single entry list" notion. If CPU2 sees anything in smk_next
it should be the old smack_known.

Casey Schaufler

  parent reply index

Thread overview: 8+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2007-10-17  4:17 Casey Schaufler
2007-10-18  4:57 ` Al Viro
2007-10-18  5:10   ` Al Viro
2007-10-19 12:39     ` Ahmed S. Darwish
2007-10-18 20:13   ` Casey Schaufler [this message]
2007-10-18 20:26     ` Al Viro
2007-10-21  1:40 ` [PATCH] Smackv8: Omit non-cipso labels in cipso_seq_start Ahmed S. Darwish
2007-10-21  2:25   ` [PATCH] Smackv8: Safe lockless {cipso,load} read operation Ahmed S. Darwish

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \ \ \ \ \ \ \ \

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

LKML Archive on

Archives are clonable:
	git clone --mirror lkml/git/0.git
	git clone --mirror lkml/git/1.git
	git clone --mirror lkml/git/2.git
	git clone --mirror lkml/git/3.git
	git clone --mirror lkml/git/4.git
	git clone --mirror lkml/git/5.git
	git clone --mirror lkml/git/6.git
	git clone --mirror lkml/git/7.git
	git clone --mirror lkml/git/8.git
	git clone --mirror lkml/git/9.git
	git clone --mirror lkml/git/10.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 lkml lkml/ \
	public-inbox-index lkml

Example config snippet for mirrors

Newsgroup available over NNTP:

AGPL code for this site: git clone