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From:   Oded Gabbay <oded.gabbay@gmail.com>
Date:   Sat, 8 May 2021 11:34:14 +0300
Message-ID: <CAFCwf11LKxvM+ixvmjsB9xHbmukKeFCouT-eNLRGEEFSGnzXQQ@mail.gmail.com>
Subject: Re: [PATCH] habanalabs/gaudi: Fix a potential use after free in gaudi_memset_device_memory
To:     Lv Yunlong <lyl2019@mail.ustc.edu.cn>
Cc:     Oded Gabbay <ogabbay@kernel.org>, Arnd Bergmann <arnd@arndb.de>,
        Ofir Bitton <obitton@habana.ai>,
        "Linux-Kernel@Vger. Kernel. Org" <linux-kernel@vger.kernel.org>
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On Mon, Apr 26, 2021 at 4:44 PM Lv Yunlong <lyl2019@mail.ustc.edu.cn> wrote:
>
> Our code analyzer reported a uaf.
>
> In gaudi_memset_device_memory, cb is get via hl_cb_kernel_create()
> with 2 refcount.
> If hl_cs_allocate_job() failed, the execution runs into release_cb
> branch. One ref of cb is dropped by hl_cb_put(cb) and could be freed
> if other thread also drops one ref. Then cb is used by cb->id later,
> which is a potential uaf.
>
> My patch add a variable 'id' to accept the value of cb->id before the
> hl_cb_put(cb) is called, to avoid the potential uaf.
>
> Fixes: 423815bf02e25 ("habanalabs/gaudi: remove PCI access to SM block")
> Signed-off-by: Lv Yunlong <lyl2019@mail.ustc.edu.cn>
> ---
>  drivers/misc/habanalabs/gaudi/gaudi.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/misc/habanalabs/gaudi/gaudi.c b/drivers/misc/habanalabs/gaudi/gaudi.c
> index 9152242778f5..ecdedd87f8cc 100644
> --- a/drivers/misc/habanalabs/gaudi/gaudi.c
> +++ b/drivers/misc/habanalabs/gaudi/gaudi.c
> @@ -5546,6 +5546,7 @@ static int gaudi_memset_device_memory(struct hl_device *hdev, u64 addr,
>         struct hl_cs_job *job;
>         u32 cb_size, ctl, err_cause;
>         struct hl_cb *cb;
> +       u64 id;
>         int rc;
>
>         cb = hl_cb_kernel_create(hdev, PAGE_SIZE, false);
> @@ -5612,8 +5613,9 @@ static int gaudi_memset_device_memory(struct hl_device *hdev, u64 addr,
>         }
>
>  release_cb:
> +       id = cb->id;
>         hl_cb_put(cb);
> -       hl_cb_destroy(hdev, &hdev->kernel_cb_mgr, cb->id << PAGE_SHIFT);
> +       hl_cb_destroy(hdev, &hdev->kernel_cb_mgr, id << PAGE_SHIFT);
>
>         return rc;
>  }
> --
> 2.25.1
>
>
Reviewed-by: Oded Gabbay <ogabbay@kernel.org>

Thanks for catching this.
Applied to -fixes.
Oded