rds: Prevent kernel-infoleak in rds_notify_queue_get()

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: e424af85ffaa ("rds: fix a leak of kernel memory")
Fixes: 6a8e52eba9d0 ("RDS: recv.c")
Suggested-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Peilin Ye <yepeilin.cs@gmail.com>
Acked-by: Santosh Shilimkar <santosh.shilimkar@oracle.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/rds/recv.c b/net/rds/recv.c
index c8404971d5ab337a39e344444c32887fc61616a2..aba4afe4dfedc22a6bdb45893f07a4d76f6cc2ed 100644 (file)
--- a/net/rds/recv.c
+++ b/net/rds/recv.c
@@ -450,12 +450,13 @@ static int rds_still_queued(struct rds_sock *rs, struct rds_incoming *inc,
 int rds_notify_queue_get(struct rds_sock *rs, struct msghdr *msghdr)
 {
        struct rds_notifier *notifier;
-       struct rds_rdma_notify cmsg = { 0 }; /* fill holes with zero */
+       struct rds_rdma_notify cmsg;
        unsigned int count = 0, max_messages = ~0U;
        unsigned long flags;
        LIST_HEAD(copy);
        int err = 0;
 
+       memset(&cmsg, 0, sizeof(cmsg)); /* fill holes with zero */
 
        /* put_cmsg copies to user space and thus may sleep. We can't do this
         * with rs_lock held, so first grab as many notifications as we can stuff