linux-kernel - Re: [RFC PATCH v3] audit: use proper refcount locking on audit

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Date:   Tue, 13 Dec 2016 15:50:18 -0500
From:   Paul Moore <paul@...l-moore.com>
To:     Richard Guy Briggs <rgb@...hat.com>
Cc:     netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-audit@...hat.com, edumazet@...gle.com,
        xiyou.wangcong@...il.com, dvyukov@...gle.com
Subject: Re: [RFC PATCH v3] audit: use proper refcount locking on audit_sock

On Tue, Dec 13, 2016 at 10:03 AM, Richard Guy Briggs <rgb@...hat.com> wrote:
> Resetting audit_sock appears to be racy.
>
> audit_sock was being copied and dereferenced without using a refcount on
> the source sock.
>
> Bump the refcount on the underlying sock when we store a refrence in
> audit_sock and release it when we reset audit_sock.  audit_sock
> modification needs the audit_cmd_mutex.
>
> See: https://lkml.org/lkml/2016/11/26/232
>
> Thanks to Eric Dumazet <edumazet@...gle.com> and Cong Wang
> <xiyou.wangcong@...il.com> on ideas how to fix it.
>
> Signed-off-by: Richard Guy Briggs <rgb@...hat.com>
> ---
> There has been a lot of change in the audit code that is about to go
> upstream to address audit queue issues.  This patch is based on the
> source tree: git://git.infradead.org/users/pcmoore/audit#next
> ---
>  kernel/audit.c |   28 +++++++++++++++++++++++-----
>  1 files changed, 23 insertions(+), 5 deletions(-)

This looks more reasonable.  I still wonder about synchronization
between threads changing the audit_* connection variables and the
kauditd_thread, but I guess we can treat that as another issue; this
patch fixes a bug and is worth merging now.

I'm building a test kernel right now, assuming nothing blows up I'll
push this patch with the rest of the audit patches tomorrow; if
something bad happens, this is going to miss the first audit pull
request.

> diff --git a/kernel/audit.c b/kernel/audit.c
> index f20eee0..3bb4126 100644
> --- a/kernel/audit.c
> +++ b/kernel/audit.c
> @@ -446,14 +446,19 @@ static void kauditd_retry_skb(struct sk_buff *skb)
>   * Description:
>   * Break the auditd/kauditd connection and move all the records in the retry
>   * queue into the hold queue in case auditd reconnects.
> + * The audit_cmd_mutex must be held when calling this function.
>   */

Don't resend, but in the future please start comments like this on the
previous line.