linux-kernel - Re: [PATCH] nvme: fix NULL pointer dereference

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Date:   Thu, 17 Sep 2020 12:56:59 -0400
From:   Tong Zhang <ztong0001@...il.com>
To:     Keith Busch <kbusch@...nel.org>
Cc:     Jens Axboe <axboe@...com>, Christoph Hellwig <hch@....de>,
        Sagi Grimberg <sagi@...mberg.me>,
        linux-nvme@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] nvme: fix NULL pointer dereference

The command_id in CQE is writable by NVMe controller, driver should
check its sanity before using it.
- Tong

On Wed, Sep 16, 2020 at 12:54 PM Keith Busch <kbusch@...nel.org> wrote:
>
> On Wed, Sep 16, 2020 at 11:36:49AM -0400, Tong Zhang wrote:
> > @@ -960,6 +960,8 @@ static inline void nvme_handle_cqe(struct nvme_queue *nvmeq, u16 idx)
> >       }
> >
> >       req = blk_mq_tag_to_rq(nvme_queue_tagset(nvmeq), cqe->command_id);
> > +     if (!req)
> > +             return;
>
> As I mentioned before, blk_mq_tag_to_rq() returns NULL if the tag
> exceeds the depth. We already verify the tag prior to calling this
> function, so what's the real root cause for how we're winding up with
> NULL here? I'm only asking this because it sounds like there's a bug
> somewhere else and this change is masking over it.
>
>
> >       trace_nvme_sq(req, cqe->sq_head, nvmeq->sq_tail);
> >       if (!nvme_try_complete_req(req, cqe->status, cqe->result))
> >               nvme_pci_complete_rq(req);