linux-kernel - Re: [PATCH] security: don't use RCU accessors for cred->session

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Date:   Thu, 11 Apr 2019 03:29:07 +1000 (AEST)
From:   James Morris <jmorris@...ei.org>
To:     Jann Horn <jannh@...gle.com>
cc:     David Howells <dhowells@...hat.com>,
        "Serge E. Hallyn" <serge@...lyn.com>, linux-kernel@...r.kernel.org,
        keyrings@...r.kernel.org, linux-security-module@...r.kernel.org
Subject: Re: [PATCH] security: don't use RCU accessors for
 cred->session_keyring

On Wed, 27 Mar 2019, Jann Horn wrote:

> sparse complains that a bunch of places in kernel/cred.c access
> cred->session_keyring without the RCU helpers required by the __rcu
> annotation.
> 
> cred->session_keyring is written in the following places:
> 
>  - prepare_kernel_cred() [in a new cred struct]
>  - keyctl_session_to_parent() [in a new cred struct]
>  - prepare_creds [in a new cred struct, via memcpy]
>  - install_session_keyring_to_cred()
>   - from install_session_keyring() on new creds
>   - from join_session_keyring() on new creds [twice]
>   - from umh_keys_init()
>    - from call_usermodehelper_exec_async() on new creds
> 
> All of these writes are before the creds are committed; therefore,
> cred->session_keyring doesn't need RCU protection.
> 
> Remove the __rcu annotation and fix up all existing users that use __rcu.
> 
> Signed-off-by: Jann Horn <jannh@...gle.com>

Applied to
git://git.kernel.org/pub/scm/linux/kernel/git/jmorris/linux-security.git next-general


-- 
James Morris
<jmorris@...ei.org>