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

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:

quoted

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.

regards,
dan carpenter