From: Paul Moore <paul@paul-moore.com>
To: Ondrej Mosnacek <omosnace@redhat.com>
Cc: Tyler Hicks <tyhicks@linux.microsoft.com>,
Stephen Smalley <stephen.smalley.work@gmail.com>,
SElinux list <selinux@vger.kernel.org>,
Linux kernel mailing list <linux-kernel@vger.kernel.org>
Subject: Re: [BUG] Race between policy reload sidtab conversion and live conversion
Date: Mon, 1 Mar 2021 09:46:39 -0500 [thread overview]
Message-ID: <CAHC9VhQ_oS-uGxhWBOCf3QBLpKD2_0--9nFOqANL1ykfbaA3Jw@mail.gmail.com> (raw)
In-Reply-To: <CAFqZXNufVGD0Sf-K3dKFmJyDOKGPg5jdJ_FPbQz__T8jAHhgYw@mail.gmail.com>
On Mon, Mar 1, 2021 at 5:36 AM Ondrej Mosnacek <omosnace@redhat.com> wrote:
> On Sun, Feb 28, 2021 at 8:21 PM Paul Moore <paul@paul-moore.com> wrote:
> > On Fri, Feb 26, 2021 at 6:12 AM Ondrej Mosnacek <omosnace@redhat.com> wrote:
> > > On Fri, Feb 26, 2021 at 2:07 AM Paul Moore <paul@paul-moore.com> wrote:
> > > > On Wed, Feb 24, 2021 at 4:35 AM Ondrej Mosnacek <omosnace@redhat.com> wrote:
...
> > Ah, yes, you're right. I was only thinking about the problem of
> > adding an entry to the old sidtab, and not the (much more likely case)
> > of an entry being added to the new sidtab. Bummer.
> >
> > Thinking aloud for a moment - what if we simply refused to add new
> > sidtab entries if the task's sidtab pointer is "old"? Common sense
> > would tell us that this scenario should be very rare at present, and I
> > believe the testing mentioned in this thread adds some weight to that
> > claim. After all, this only affects tasks which entered into their
> > RCU protected session prior to the policy load RCU sync *AND* are
> > attempting to add a new entry to the sidtab. That *has* to be a
> > really low percentage, especially on a system that has been up and
> > running for some time. My gut feeling is this should be safe as well;
> > all of the calling code should have the necessary error handling in
> > place as there are plenty of reasons why we could normally fail to add
> > an entry to the sidtab; memory allocation failures being the most
> > obvious failure point I would suspect. This obvious downside to such
> > an approach is that those operations which do meet this criteria would
> > fail - and we should likely emit an error in this case - but is this
> > failure really worse than any other transient kernel failure,
>
> No, I don't like this approach at all. Before the sidtab refactor, it
> had been done exactly this way ...
I recognize I probably haven't made my feelings about reverts clear,
or if I have, I haven't done so recently. Let me fix that now: I
*hate* them. Further I hate reverts with a deep, passionate hatred
that I reserve for very few things. Maybe we have to revert this
change, even though I *hate* reverts they do remain an option; you
just need to be 99% sure you've exhausted all the other options first.
> Perhaps it wasn't clear from what I wrote, but I certainly don't want
> to abandon it completely. Just to revert to a safe state until we
> figure out how to do the RCU policy reload safely. The solution with
> two-way conversion seems doable, it's just not a quick and easy fix.
I suggest pursuing this before the revert to see what it looks like
and we can discuss it further during review.
--
paul moore
www.paul-moore.com
next prev parent reply other threads:[~2021-03-01 14:48 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-02-23 21:43 [BUG] Race between policy reload sidtab conversion and live conversion Tyler Hicks
2021-02-23 21:50 ` Tyler Hicks
2021-02-23 22:36 ` Tyler Hicks
2021-02-24 0:02 ` Paul Moore
2021-02-24 9:33 ` Ondrej Mosnacek
2021-02-24 14:36 ` Tyler Hicks
2021-02-25 16:38 ` Ondrej Mosnacek
2021-02-25 16:45 ` Tyler Hicks
2021-02-25 23:27 ` Paul Moore
2021-02-26 1:06 ` Paul Moore
2021-02-26 11:11 ` Ondrej Mosnacek
2021-02-28 19:21 ` Paul Moore
2021-03-01 10:35 ` Ondrej Mosnacek
2021-03-01 14:46 ` Paul Moore [this message]
[not found] ` <20210226040542.1137-1-hdanton@sina.com>
2021-02-26 11:19 ` Ondrej Mosnacek
[not found] ` <20210227023524.15844-1-hdanton@sina.com>
2021-03-01 14:35 ` Ondrej Mosnacek
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:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=CAHC9VhQ_oS-uGxhWBOCf3QBLpKD2_0--9nFOqANL1ykfbaA3Jw@mail.gmail.com \
--to=paul@paul-moore.com \
--cc=linux-kernel@vger.kernel.org \
--cc=omosnace@redhat.com \
--cc=selinux@vger.kernel.org \
--cc=stephen.smalley.work@gmail.com \
--cc=tyhicks@linux.microsoft.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).