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

[HÃkon Bugge]

> On 31 Jul 2020, at 11:59, Dan Carpenter <dan.carpenter@xxxxxxxxxx> 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, HÃkon


> regards,
> dan carpenter
>