Re: [PATCH v12 13/26] userns: Add pointer to ima_namespace to user_namespace

[Christian Brauner <brauner@kernel.org>]

On Sun, May 22, 2022 at 01:24:26PM -0500, Serge Hallyn wrote:
> On Wed, Apr 20, 2022 at 10:06:20AM -0400, Stefan Berger wrote:
> > Add a pointer to ima_namespace to the user_namespace and initialize
> > the init_user_ns with a pointer to init_ima_ns. We need a pointer from
> > the user namespace to its associated IMA namespace since IMA namespaces
> > are piggybacking on user namespaces.
> > 
> > Signed-off-by: Stefan Berger <stefanb@linux.ibm.com>
> > Acked-by: Christian Brauner <brauner@kernel.org>
> > Reviewed-by: Mimi Zohar <zohar@linux.ibm.com>
> > 
> > ---
> > v11:
> >  - Added lost A-b from Christian back
> >  - Added sentence to patch description explaining why we need the pointer
> > 
> > v9:
> >  - Deferred implementation of ima_ns_from_user_ns() to later patch
> > ---
> >  include/linux/ima.h            | 2 ++
> >  include/linux/user_namespace.h | 4 ++++
> >  kernel/user.c                  | 4 ++++
> >  3 files changed, 10 insertions(+)
> > 
> > diff --git a/include/linux/ima.h b/include/linux/ima.h
> > index 426b1744215e..fcb60a44e05f 100644
> > --- a/include/linux/ima.h
> > +++ b/include/linux/ima.h
> > @@ -14,6 +14,8 @@
> >  #include <crypto/hash_info.h>
> >  struct linux_binprm;
> >  
> > +extern struct ima_namespace init_ima_ns;
> > +
> >  #ifdef CONFIG_IMA
> >  extern enum hash_algo ima_get_current_hash_algo(void);
> >  extern int ima_bprm_check(struct linux_binprm *bprm);
> > diff --git a/include/linux/user_namespace.h b/include/linux/user_namespace.h
> > index 33a4240e6a6f..019e8cf7b633 100644
> > --- a/include/linux/user_namespace.h
> > +++ b/include/linux/user_namespace.h
> > @@ -36,6 +36,7 @@ struct uid_gid_map { /* 64 bytes -- 1 cache line */
> >  #define USERNS_INIT_FLAGS USERNS_SETGROUPS_ALLOWED
> >  
> >  struct ucounts;
> > +struct ima_namespace;
> >  
> >  enum ucount_type {
> >  	UCOUNT_USER_NAMESPACES,
> > @@ -99,6 +100,9 @@ struct user_namespace {
> >  #endif
> >  	struct ucounts		*ucounts;
> >  	long ucount_max[UCOUNT_COUNTS];
> > +#ifdef CONFIG_IMA_NS
> 
> It's probably worth putting a comment here saying that user_ns does not
> pin ima_ns.
> 
> That the only time the ima_ns will be freed is when user_ns is freed,
> and only time it will be changed is when user_ns is freed, or during
> ima_fs_ns_init() (under smp_load_acquire) during a new mount.
> 
> > +	struct ima_namespace	*ima_ns;
> 
> So, if I create a new user_ns with a new ima_ns, and in there I
> create a new user_ns again, it looks like ima_ns will be NULL in
> the new user_ns?  Should it not be set to the parent->ima_ns?
> (which would cause trouble for the way it's currently being
> freed...)

Would also work and wouldn't be difficult to do imho.