Re: [Linux-kernel-mentees] [PATCH net] rds: Prevent kernel-infoleak in rds_notify_queue_get()

Håkon Bugge
2020-07-31T11:14:35Z

> On 31 Jul 2020, at 11:59, Dan Carpenter <dan.carpenter@oracle.com> wrote:
>
> On Fri, Jul 31, 2020 at 07:53:01AM +0300, Leon Romanovsky wrote:
>> On Thu, Jul 30, 2020 at 03:20:26PM -0400, Peilin Ye wrote:
>>> rds_notify_queue_get() is potentially copying uninitialized kernel stack
>>> memory to userspace since the compiler may leave a 4-byte hole at the end
>>> of `cmsg`.
>>>
>>> In 2016 we tried to fix this issue by doing `= { 0 };` on `cmsg`, which
>>> unfortunately does not always initialize that 4-byte hole. Fix it by using
>>> memset() instead.
>>
>> Of course, this is the difference between "{ 0 }" and "{}" initializations.
>>
>
> No, there is no difference. Even struct assignments like:
>
> foo = *bar;
>
> can leave struct holes uninitialized. Depending on the compiler the
> assignment can be implemented as a memset() or as a series of struct
> member assignments.

What about:

struct rds_rdma_notify {
__u64 user_token;
__s32 status;
} __attribute__((packed));

Thxs, Håkon

> regards,
> dan carpenter
>