[Drbd-dev] [bug report] drbd: Backport the "events2" command

[Dan Carpenter <dan.carpenter@oracle.com>]

Hello Andreas Gruenbacher,

The patch a29728463b25: "drbd: Backport the "events2" command" from
Jul 31, 2014, leads to the following static checker warning:

	drivers/block/drbd/drbd_nl.c:4934 get_initial_state()
	error: dereferencing freed memory 'skb'

drivers/block/drbd/drbd_nl.c
  4841  static void notify_initial_state_done(struct sk_buff *skb, unsigned int seq)
  4842  {
  4843          struct drbd_genlmsghdr *dh;
  4844          int err;
  4845  
  4846          err = -EMSGSIZE;
  4847          dh = genlmsg_put(skb, 0, seq, &drbd_genl_family, 0, DRBD_INITIAL_STATE_DONE);
  4848          if (!dh)
  4849                  goto nla_put_failure;
  4850          dh->minor = -1U;
  4851          dh->ret_code = NO_ERROR;
  4852          if (nla_put_notification_header(skb, NOTIFY_EXISTS))
  4853                  goto nla_put_failure;
  4854          genlmsg_end(skb, dh);
  4855          return;
  4856  
  4857  nla_put_failure:
  4858          nlmsg_free(skb);

We free this on error, but it's a void function so it seems like the
callers just assume it succeeded leading to a use after free bug.

(It's also possible that I have misunderstood the refcounting here).

  4859          pr_err("Error %d sending event. Event seq:%u\n", err, seq);
  4860  }

regards,
dan carpenter