Re: [RFC PATCH 15/17] perf: Allow controlled non-root access to detached events

[Peter Zijlstra]

On Tue, Sep 05, 2017 at 04:30:24PM +0300, Alexander Shishkin wrote:
> @@ -5587,7 +5587,13 @@ static int perf_open(struct inode *inode, struct file *file)
>  	if (!atomic_long_inc_not_zero(&event->refcount))
>  		return -ENOENT;
>  
> -	ret = simple_open(inode, file);
> +	/* event's user is stable while we're holding the reference */
> +	if (event->rb->mmap_user != current_user() &&
> +	    !capable(CAP_SYS_ADMIN))
> +		ret = -EACCES;
> +
> +	if (!ret)
> +		ret = simple_open(inode, file);
>  	if (ret)
>  		put_event(event);
>  

> @@ -11530,6 +11537,18 @@ static int perf_instance_unlink(const char *name)
>  	if (!event)
>  		return -EINVAL;
>  
> +	if (!atomic_long_inc_not_zero(&event->refcount))
> +		return 0;
> +
> +	/* event's user is stable while we're holding the reference */
> +	if (event->rb->mmap_user != current_user() &&
> +	    !capable(CAP_SYS_ADMIN))
> +		ret = -EACCES;
> +	put_event(event);
> +
> +	if (ret)
> +		return ret;
> +
>  	if (!(event->attach_state & PERF_ATTACH_CONTEXT))
>  		return -EBUSY;
>  

Why aren't we using regular file permissions for this?