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

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Message-ID: <e3a867a8-284b-7250-b1b2-1956f533f6b0@quicinc.com>
Date:   Mon, 12 Jun 2023 18:33:04 +0530
From:   Pranjal Ramajor Asha Kanojiya <quic_pkanojiy@...cinc.com>
To:     Christian König <christian.koenig@....com>,
        "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>, <kernel-janitors@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <dri-devel@...ts.freedesktop.org>,
        <linaro-mm-sig@...ts.linaro.org>, <linux-media@...r.kernel.org>
Subject: Re: [PATCH] accel/qaic: Fix dereferencing freed memory



On 6/12/2023 4:52 PM, Christian König wrote:
> 
> 
> 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.

Driver uses drm_gem_prime_fd_to_handle() helper function but it also 
registers for ->gem_prime_import() which is internally called by 
drm_gem_prime_fd_to_handle(). All the operations done in 
gem_prime_import() are undone here.

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