linux-kernel - Re: [PATCH] accel/qaic: Fix dereferencing freed memory

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Date:   Mon, 12 Jun 2023 13:22:43 +0200
From:   Christian König <christian.koenig@....com>
To:     Sukrut Bellary <sukrut.bellary@...ux.com>,
        Jeffrey Hugo <quic_jhugo@...cinc.com>,
        Oded Gabbay <ogabbay@...nel.org>,
        Sumit Semwal <sumit.semwal@...aro.org>
Cc:     linux-arm-msm@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        linaro-mm-sig@...ts.linaro.org, linux-media@...r.kernel.org,
        linux-kernel@...r.kernel.org, kernel-janitors@...r.kernel.org
Subject: Re: [PATCH] accel/qaic: Fix dereferencing freed memory



Am 10.06.23 um 04:12 schrieb Sukrut Bellary:
> smatch warning:
> 	drivers/accel/qaic/qaic_data.c:620 qaic_free_object() error:
> 		dereferencing freed memory 'obj->import_attach'
>
> obj->import_attach is detached and freed using dma_buf_detach().
> But used after free to decrease the dmabuf ref count using
> dma_buf_put().
>
> Fixes: ff13be830333 ("accel/qaic: Add datapath")
> Signed-off-by: Sukrut Bellary <sukrut.bellary@...ux.com>
> ---
>   drivers/accel/qaic/qaic_data.c | 4 +++-
>   1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/accel/qaic/qaic_data.c b/drivers/accel/qaic/qaic_data.c
> index e42c1f9ffff8..7cba4d680ea8 100644
> --- a/drivers/accel/qaic/qaic_data.c
> +++ b/drivers/accel/qaic/qaic_data.c
> @@ -613,11 +613,13 @@ static int qaic_gem_object_mmap(struct drm_gem_object *obj, struct vm_area_struc
>   static void qaic_free_object(struct drm_gem_object *obj)
>   {
>   	struct qaic_bo *bo = to_qaic_bo(obj);
> +	struct dma_buf *dmabuf;

Maybe move that variable into the if.

>   
>   	if (obj->import_attach) {
>   		/* DMABUF/PRIME Path */
> +		dmabuf = obj->import_attach->dmabuf;
>   		dma_buf_detach(obj->import_attach->dmabuf, obj->import_attach);
> -		dma_buf_put(obj->import_attach->dmabuf);
> +		dma_buf_put(dmabuf);

I strongly assume you are not using the GEM prime helpers for this?

Christian.

>   	} else {
>   		/* Private buffer allocation path */
>   		qaic_free_sgt(bo->sgt);