[PATCH] dma-buf: Fix possible UAF in dma_buf_export

[cuigaosheng]

Thanks T.J and Christian, thanks everyone for taking time to review this patch.

Charan, actually I don't have a good patch to to fix it, if you can submit
a new patch to solve it, please feel free to do it.

By the way, I'd appreciate it if you could send to me the new patch when you submit it.

Thanks again!

Gaosheng.

On 2022/11/24 13:56, Charan Teja Kalla wrote:
> Thanks T.J and Christian for the inputs.
>
> On 11/19/2022 7:00 PM, Christian König wrote:
>>>      Yes, exactly that's the idea.
>>>
>>>      The only alternatives I can see would be to either move allocating
>>>      the
>>>      file and so completing the dma_buf initialization last again or just
>>>      ignore errors from sysfs.
>>>
>>>      > If we still want to avoid calling dmabuf->ops->release(dmabuf) in
>>>      > dma_buf_release like the comment says I guess we could use
>>>      sysfs_entry
>>>      > and ERR_PTR to flag that, otherwise it looks like we'd need a bit
>>>      > somewhere.
>>>
>>>      No, this should be dropped as far as I can see. The sysfs cleanup
>>>      code
>>>      looks like it can handle not initialized kobj pointers.
>>>
>>>
>>> Yeah there is also the null check in dma_buf_stats_teardown() that
>>> would prevent it from running, but I understood the comment to be
>>> referring to the release() dma_buf_ops call into the exporter which
>>> comes right after the teardown call. That looks like it's preventing
>>> the fput task work calling back into the exporter after the exporter
>>> already got an error from dma_buf_export(). Otherwise the exporter
>>> sees a release() for a buffer that it doesn't know about / thinks
>>> shouldn't exist. So I could imagine an exporter trying to double free:
>>> once for the failed dma_buf_export() call, and again when the
>>> release() op is called later.
>>
>> Oh, very good point as well. Yeah, then creating the file should
>> probably come last.
>>
> @Gaosheng: Could you please make these changes or you let me to do?
>
>> Regards,
>> Christian.
> .