On 7/30/20 12:20 PM, 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.

Cc: stable@vger.kernel.org
Fixes: f037590fff30 ("rds: fix a leak of kernel memory")
Fixes: bdbe6fbc6a2f ("RDS: recv.c")
Suggested-by: Dan Carpenter <redacted>
Signed-off-by: Peilin Ye <redacted>
---
Note: the "real" copy_to_user() happens in put_cmsg(), where
`cmlen - sizeof(*cm)` equals to `sizeof(cmsg)`.

Reference: https://lwn.net/Articles/417989/

$ pahole -C "rds_rdma_notify" net/rds/recv.o
struct rds_rdma_notify {
	__u64                      user_token;           /*     0     8 */
	__s32                      status;               /*     8     4 */

	/* size: 16, cachelines: 1, members: 2 */
	/* padding: 4 */
	/* last cacheline: 16 bytes */
};

  net/rds/recv.c | 3 ++-
  1 file changed, 2 insertions(+), 1 deletion(-)

Looks good.
FWIW,
Acked-by: Santosh Shilimkar <redacted>