[PATCH v7 4/4] Netlink: handle multi netlink messages

[Fabien Siron]

Quoting Dmitry V. Levin (2016-06-23 11:36:25)
> On Thu, Jun 23, 2016 at 10:49:53AM +0000, Fabien Siron wrote:
> > Quoting Dmitry V. Levin (2016-06-22 17:40:39)
> > > On Wed, Jun 22, 2016 at 01:27:06PM +0000, Fabien Siron wrote:
[...]
> > > > +     if (NLMSG_ALIGN(nlmsghdr->nlmsg_len) == 0 ||
> > > > +         NLMSG_ALIGN(nlmsghdr->nlmsg_len) > *len)
> > > > +             return 0;
> > > 
> > > This is not going to happen with current implementation of nlmsg_fetch,
> > > but if nlmsg_fetch changes and if this condition is true, then
> > > *len remains unchanged and the subsequent nlmsg_fetch prints NULL.
> > 
> > A way to fix that is to put *len to 0 in this test. But the problem is that
> > nothing will be printed if sizeof(struct nlmsghdr) < *len < nlmsghdr->nlmsg_len.
> 
> It's up to decode_netlink_msg to decide how to print such messages.
> 
> decode_netlink has to be consistent.  Every successfully fetched struct
> nlmsghdr should be printed.  When decode_netlink leaves some bytes of the
> message undecoded, it has to print an indication.

It already prints a string, what kind of indication do you want to add?

So do you agree with this test for next_nlmsghdr:

if (NLMSG_ALIGN(nlmsghdr->nlmsg_len) == 0 ||
    NLMSG_ALIGN(nlmsghdr->nlmsg_len) > *len) {
    *len = nlmsghdr->nlmsg_len;
    return 0;
}

Now, the subsequent nlmsg_fetch does not print NULL.

Regards,
--
Fabien Siron