linux-kernel - Re: [PATCH] blk-cgroup: check blkcg policy is enabled in blkg

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <YWRxi2OaIHhG9rOc@slm.duckdns.org>
Date:   Mon, 11 Oct 2021 07:16:59 -1000
From:   Tejun Heo <tj@...nel.org>
To:     Yu Kuai <yukuai3@...wei.com>
Cc:     axboe@...nel.dk, cgroups@...r.kernel.org,
        linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
        yi.zhang@...wei.com
Subject: Re: [PATCH] blk-cgroup: check blkcg policy is enabled in
 blkg_create()

On Fri, Oct 08, 2021 at 03:27:20PM +0800, Yu Kuai wrote:
> diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c
> index eb48090eefce..00e1d97621ea 100644
> --- a/block/blk-cgroup.c
> +++ b/block/blk-cgroup.c
> @@ -226,6 +226,20 @@ struct blkcg_gq *blkg_lookup_slowpath(struct blkcg *blkcg,
>  }
>  EXPORT_SYMBOL_GPL(blkg_lookup_slowpath);
>  
> +static void blkg_check_pd(struct request_queue *q, struct blkcg_gq *blkg)
> +{
> +	int i;
> +
> +	for (i = 0; i < BLKCG_MAX_POLS; i++) {
> +		struct blkcg_policy *pol = blkcg_policy[i];
> +
> +		if (blkg->pd[i] && !blkcg_policy_enabled(q, pol)) {
> +			pol->pd_free_fn(blkg->pd[i]);
> +			blkg->pd[i] = NULL;
> +		}
> +	}
> +}
> +
>  /*
>   * If @new_blkg is %NULL, this function tries to allocate a new one as
>   * necessary using %GFP_NOWAIT.  @new_blkg is always consumed on return.
> @@ -252,6 +266,9 @@ static struct blkcg_gq *blkg_create(struct blkcg *blkcg,
>  		goto err_free_blkg;
>  	}
>  
> +	if (new_blkg)
> +		blkg_check_pd(q, new_blkg);
> +

Can't this happen the other way around too? ie. Linking a pd which doesn't
have an entry for a policy which got enabled inbetween? And what if an
existing policy was de-registered and another policy got the policy id
inbetween? I think the correct solution here would be synchronizing alloc -
create blocks against policy deactivation rather than trying to patch an
allocated blkg later. Deactivation being a really slow path, there are
plenty of options. The main challenge would making it difficult to make
mistakes with, I guess.

Thanks.

-- 
tejun