[PATCH] accel/qaic: Fix dereferencing freed memory
Jeffrey Hugo
quic_jhugo at quicinc.com
Mon Jun 12 15:09:39 UTC 2023
On 6/12/2023 7:21 AM, Christian König wrote:
> Am 12.06.23 um 15:03 schrieb Pranjal Ramajor Asha Kanojiya:
>>
>>
>> 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 at linux.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.
>
> Then why don't you use drm_prime_gem_destroy() which is the cleanup
> helper for imports created by ->gem_prime_import() ?
>
> That looks pretty much identical to what you do here manually.
I think destroy() wasn't used because we are new to DRM and sometimes
confused by the multitude of options. I appreciate the suggestion and
will follow up to see if destroy() will work here, or identify what
would prevent the use of it.
-Jeff
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