Re: [PATCH] perf_event: Add support for LSM and SELinux checks

[Joel Fernandes <joel@joelfernandes.org>]

On Mon, Oct 14, 2019 at 11:35:44AM +0200, Peter Zijlstra wrote:
> On Fri, Oct 11, 2019 at 12:03:30PM -0400, Joel Fernandes (Google) wrote:
> 
> > @@ -4761,6 +4762,7 @@ int perf_event_release_kernel(struct perf_event *event)
> >  	}
> >  
> >  no_ctx:
> > +	security_perf_event_free(event);
> >  	put_event(event); /* Must be the 'last' reference */
> >  	return 0;
> >  }
> 
> > @@ -10553,11 +10568,16 @@ perf_event_alloc(struct perf_event_attr *attr, int cpu,
> >  		}
> >  	}
> >  
> > +	err = security_perf_event_alloc(event);
> > +	if (err)
> > +		goto err_security;
> > +
> >  	/* symmetric to unaccount_event() in _free_event() */
> >  	account_event(event);
> >  
> >  	return event;
> >  
> > +err_security:
> >  err_addr_filters:
> >  	kfree(event->addr_filter_ranges);
> >  
> 
> There's a bunch of problems here I think:
> 
>  - err_security is named wrong; the naming scheme is to name the label
>    after the last thing that succeeded / first thing that needs to be
>    undone.
> 
>  - per that, you're forgetting to undo 'get_callchain_buffers()'

Yes, you're right. Tested your fix below. Sorry to miss this.

>  - perf_event_release_kernel() is not a full match to
>    perf_event_alloc(), inherited events get created by
>    perf_event_alloc() but never pass through
>    perf_event_release_kernel().

Oh, through inherit_event(). Thanks for pointing this semantic out, did not
know that.

> I'm thinking the below patch on top should ammend these issues; please
> verify.

Yes, applied your diff below and verified that the events are getting freed
as they were in my initial set of tests. The diff also looks good to me.

I squashed your diff below and will resend as v3. Since you modified this
patch a lot, I will add your Co-developed-by tag as well.

thanks, Peter!

 - Joel


> ---
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -4540,6 +4540,8 @@ static void _free_event(struct perf_even
>  
>  	unaccount_event(event);
>  
> +	security_perf_event_free(event);
> +
>  	if (event->rb) {
>  		/*
>  		 * Can happen when we close an event with re-directed output.
> @@ -4774,7 +4776,6 @@ int perf_event_release_kernel(struct per
>  	}
>  
>  no_ctx:
> -	security_perf_event_free(event);
>  	put_event(event); /* Must be the 'last' reference */
>  	return 0;
>  }
> @@ -10595,14 +10596,18 @@ perf_event_alloc(struct perf_event_attr
>  
>  	err = security_perf_event_alloc(event);
>  	if (err)
> -		goto err_security;
> +		goto err_callchain_buffer;
>  
>  	/* symmetric to unaccount_event() in _free_event() */
>  	account_event(event);
>  
>  	return event;
>  
> -err_security:
> +err_callchain_buffer:
> +	if (!event->parent) {
> +		if (event->attr.sample_type & PERF_SAMPLE_CALLCHAIN)
> +			put_callchain_buffers();
> +	}
>  err_addr_filters:
>  	kfree(event->addr_filter_ranges);
>