Re: [PATCH ghak90 V9 07/13] audit: add support for non-syscall auxiliary records

[Paul Moore <paul@paul-moore.com>]

On Sat, Jun 27, 2020 at 9:22 AM Richard Guy Briggs <rgb@redhat.com> wrote:
>
> Standalone audit records have the timestamp and serial number generated
> on the fly and as such are unique, making them standalone.  This new
> function audit_alloc_local() generates a local audit context that will
> be used only for a standalone record and its auxiliary record(s).  The
> context is discarded immediately after the local associated records are
> produced.

We've had some good discussions on the list about why we can't reuse
the "in_syscall" field and need to add a "local" field, I think it
would be good to address that here in the commit description.

> Signed-off-by: Richard Guy Briggs <rgb@redhat.com>
> Acked-by: Serge Hallyn <serge@hallyn.com>
> Acked-by: Neil Horman <nhorman@tuxdriver.com>
> Reviewed-by: Ondrej Mosnacek <omosnace@redhat.com>
> ---
>  include/linux/audit.h |  8 ++++++++
>  kernel/audit.h        |  1 +
>  kernel/auditsc.c      | 33 ++++++++++++++++++++++++++++-----
>  3 files changed, 37 insertions(+), 5 deletions(-)

...

> diff --git a/kernel/auditsc.c b/kernel/auditsc.c
> index 9e79645e5c0e..935eb3d2cde9 100644
> --- a/kernel/auditsc.c
> +++ b/kernel/auditsc.c
> @@ -908,11 +908,13 @@ static inline void audit_free_aux(struct audit_context *context)
>         }
>  }
>
> -static inline struct audit_context *audit_alloc_context(enum audit_state state)
> +static inline struct audit_context *audit_alloc_context(enum audit_state state,
> +                                                       gfp_t gfpflags)
>  {
>         struct audit_context *context;
>
> -       context = kzalloc(sizeof(*context), GFP_KERNEL);
> +       /* We can be called in atomic context via audit_tg() */

At this point I think it's clear we need a respin so I'm not going to
preface all of my nitpick comments as such, although this definitely
would qualify ...

I don't believe audit_tg() doesn't exist yet, likely coming later in
this patchset, so please remove this comment as it doesn't make sense
in this context.

To be frank, don't re-add the comment later in the patchset either.
Comments like these tend to be fragile and don't really add any great
insight.  The audit_tg() function can, and most likely will, be
modified at some point in the future such that the comment above no
longer applies, and there is a reasonable chance that when it does the
above comment will not be updated.  Further, anyone modifying the
audit_alloc_context() is going to look at the callers (rather they
*should* look at the callers) and will notice the no-sleep
requirements.

> @@ -960,8 +963,27 @@ int audit_alloc_syscall(struct task_struct *tsk)
>         return 0;
>  }
>
> -static inline void audit_free_context(struct audit_context *context)
> +struct audit_context *audit_alloc_local(gfp_t gfpflags)
>  {
> +       struct audit_context *context = NULL;
> +
> +       context = audit_alloc_context(AUDIT_RECORD_CONTEXT, gfpflags);
> +       if (!context) {
> +               audit_log_lost("out of memory in audit_alloc_local");
> +               goto out;

You might as well just return NULL here, no need to jump and then return NULL.


> +       }
> +       context->serial = audit_serial();
> +       ktime_get_coarse_real_ts64(&context->ctime);
> +       context->local = true;
> +out:
> +       return context;
> +}
> +EXPORT_SYMBOL(audit_alloc_local);

--
paul moore
www.paul-moore.com