[PATCH] security: don't use RCU accessors for cred->session_keyring

[James Morris]

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 at google.com>

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


-- 
James Morris
<jmorris at namei.org>