linux-kernel - Re: [PATCH] nvme-core: remove head->effects to fix use-after-free

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Message-ID: <ZVUiLr3g1_i5YmRQ@kbusch-mbp.dhcp.thefacebook.com>
Date:   Wed, 15 Nov 2023 14:55:26 -0500
From:   Keith Busch <kbusch@...nel.org>
To:     Yuanyuan Zhong <yzhong@...estorage.com>
Cc:     Jens Axboe <axboe@...nel.dk>, hch@....de, sagi@...mberg.me,
        linux-nvme@...ts.infradead.org, linux-kernel@...r.kernel.org,
        randyj@...estorage.com, hcoutinho@...estorage.com
Subject: Re: [PATCH] nvme-core: remove head->effects to fix use-after-free

On Wed, Nov 15, 2023 at 11:21:53AM -0800, Yuanyuan Zhong wrote:
> On Wed, Nov 15, 2023 at 11:02 AM Jens Axboe <axboe@...nel.dk> wrote:
> 
> Do you mean something like this? If not, can you please elaborate
> "when we need"?
> -               struct nvme_effects_log *cel = xa_load(&ctrl->cels, ns->head->ids.csi);
> +               struct nvme_effects_log *cel = (ns->head->ids.csi == NVME_CSI_NVM) ?
> +                       ctrl->effects : xa_load(&ctrl->cels, ns->head->ids.csi);
> Will it be good to change ctrl->effects to ctrl->effects[3] for
> already defined CSI?

I suggest either re-assign the cached head->effects to one from a still
live controller when current path is removed, or move the saved effects
to the subsystem instead of the controller. All controllers in the
subsystem should be reporting the same effects log anyway, so
duplicating all that per-controller is kind of wasteful.