Re: WARNING in apparmor_cred_free

From: James Morris <jmorris@namei.org>
To: Casey Schaufler <casey@schaufler-ca.com>
Cc: John Johansen <john.johansen@canonical.com>,
	linux-kernel@vger.kernel.org,
	linux-security-module@vger.kernel.org, serge@hallyn.com
Subject: Re: WARNING in apparmor_cred_free
Date: Thu, 17 Jan 2019 08:14:45 +1100 (AEDT)	[thread overview]
Message-ID: <alpine.LRH.2.21.1901170814170.7422@namei.org> (raw)
In-Reply-To: <99cd1f6b-682e-7d1f-35ad-b9092d46323f@schaufler-ca.com>

On Fri, 11 Jan 2019, Casey Schaufler wrote:

> >From 47134986133c822e1d88860fa2b108f92c97a7ff Mon Sep 17 00:00:00 2001
> From: Casey Schaufler <casey@schaufler-ca.com>
> Date: Fri, 11 Jan 2019 17:31:50 -0800
> Subject: [PATCH 1/2] LSM: Check for NULL cred-security on free
> 
> Check that the cred security blob has been set before trying
> to clean it up. There is a case during credential initialization
> that could result in this.
> 
> Signed-off-by: Casey Schaufler <casey@schaufler-ca.com>

JJ: does this fix the problem?

> ---
>  security/security.c | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/security/security.c b/security/security.c
> index a618e22df5c6..7bffc86d4e87 100644
> --- a/security/security.c
> +++ b/security/security.c
> @@ -1477,6 +1477,13 @@ int security_cred_alloc_blank(struct cred *cred, gfp_t gfp)
>  
>  void security_cred_free(struct cred *cred)
>  {
> +	/*
> +	 * There is a failure case in prepare_creds() that
> +	 * may result in a call here with ->security being NULL.
> +	 */
> +	if (unlikely(cred->security == NULL))
> +		return;
> +
>  	call_void_hook(cred_free, cred);
>  
>  	kfree(cred->security);
> 

-- 
James Morris
<jmorris@namei.org>