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

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Date:   Mon, 12 Jun 2023 18:14:11 +0530
From:   Pranjal Ramajor Asha Kanojiya <quic_pkanojiy@...cinc.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>,
        Christian König <christian.koenig@....com>
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



On 6/10/2023 7:42 AM, Sukrut Bellary wrote:
> 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;
>   
>   	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);
>   	} else {
>   		/* Private buffer allocation path */
>   		qaic_free_sgt(bo->sgt);

Reviewed-by: Pranjal Ramajor Asha Kanojiya <quic_pkanojiy@...cinc.com>