On 08/31/2018 01:12 PM, Greg Kroah-Hartman wrote:
> On Fri, Aug 31, 2018 at 01:06:27PM -0700, Greg Hackmann wrote:
>> The ION_IOC_{MAP,SHARE} ioctls drop and reacquire client->lock several
>> times while operating on one of the client's ion_handles. This creates
>> windows where userspace can call ION_IOC_FREE on the same client with
>> the same handle, and effectively make the kernel drop its own reference.
>> For example:
>>
>> - thread A: ION_IOC_ALLOC creates an ion_handle with refcount 1
>> - thread A: starts ION_IOC_MAP and increments the refcount to 2
>> - thread B: ION_IOC_FREE decrements the refcount to 1
>> - thread B: ION_IOC_FREE decrements the refcount to 0 and frees the
>> handle
>> - thread A: continues ION_IOC_MAP with a dangling ion_handle * to
>> freed memory
>>
>> Fix this by holding client->lock for the duration of
>> ION_IOC_{MAP,SHARE}, preventing the concurrent ION_IOC_FREE. Also
>> remove ion_handle_get_by_id(), since there's literally no way to use it
>> safely.
>>
>> This patch is applied on top of 4.9.y. Kernels 4.12 and later are
>> unaffected, since all the underlying ion_handle infrastructure has been
>> ripped out.
>
> Does 4.4.y or older also need this? If so, can you send backports, as
> this one does not apply there.
>
> thanks,
>
> greg k-h
>
Yes, 4.4.y and older will need this. If there are no objections to this
patch, I'll send backports ASAP.
