[PATCH v2] binder: use cred instead of task for selinux checks

[Greg KH]

On Fri, Oct 01, 2021 at 10:55:21AM -0700, Todd Kjos wrote:
> Save the struct cred associated with a binder process
> at initial open to avoid potential race conditions
> when converting to a security ID.
> 
> Since binder was integrated with selinux, it has passed
> 'struct task_struct' associated with the binder_proc
> to represent the source and target of transactions.
> The conversion of task to SID was then done in the hook
> implementations. It turns out that there are race conditions
> which can result in an incorrect security context being used.
> 
> Fix by saving the 'struct cred' during binder_open and pass
> it to the selinux subsystem.
> 
> Fixes: 79af73079d75 ("Add security hooks to binder and implement the
> hooks for SELinux.")
> Signed-off-by: Todd Kjos <tkjos at google.com>
> Cc: stable at vger.kernel.org # 5.14+ (need backport for earlier stables)
> ---
> v2: updated comments as suggested by Paul Moore
> 
>  drivers/android/binder.c          | 14 +++++----
>  drivers/android/binder_internal.h |  4 +++
>  include/linux/lsm_hook_defs.h     | 14 ++++-----
>  include/linux/lsm_hooks.h         | 14 ++++-----
>  include/linux/security.h          | 28 +++++++++---------
>  security/security.c               | 14 ++++-----
>  security/selinux/hooks.c          | 48 +++++++++----------------------
>  7 files changed, 60 insertions(+), 76 deletions(-)

Ideally I could get an ack from the security developers before taking
this in my tree...

thanks,

greg k-h