[PATCH v3 3/7] tests: check decoding of netlink protocol

[Dmitry V. Levin]

On Fri, Jun 17, 2016 at 02:32:02PM +0000, Fabien Siron wrote:
> Quoting Dmitry V. Levin (2016-06-16 14:54:58)
> > On Thu, Jun 16, 2016 at 02:20:07PM +0000, Fabien Siron wrote:
> > > Quoting Dmitry V. Levin (2016-06-16 10:40:18)
> > > > On Wed, Jun 15, 2016 at 12:43:01PM +0000, Fabien Siron wrote:
> > > > [...]
> > > > > +static void
> > > > > +send_query(const int fd, const unsigned int pid_magic)
> > > > > +{
> > > > > +     struct {
> > > > > +             struct nlmsghdr nlh;
> > > > > +             char magic[4];
> > > > > +     } req = {
> > > > > +             .nlh = {
> > > > > +                     .nlmsg_len = sizeof(req),
> > > > > +                     .nlmsg_type = NLMSG_NOOP,
> > > > > +                     .nlmsg_flags = NLM_F_DUMP | NLM_F_REQUEST
> > > > > +             },
> > > > > +             .magic = "abcd"
> > > > > +     };
> > > > > +
> > > > > +     if (sendto(fd, &req, sizeof(req), MSG_DONTWAIT, NULL, 0) !=
> > > > > +         (unsigned) sizeof(req))
> > > > > +             perror_msg_and_skip("sendto");
> > > > > +
> > > > > +     printf("sendto(%d<NETLINK:[SOCK_DIAG:%u]>, {{len=%u, type=NLMSG_NOOP, "
> > > > > +            "flags=NLM_F_REQUEST|0x%x, seq=0, pid=0}, \"abcd\"}, %u, "
> > > > > +            "MSG_DONTWAIT, NULL, 0) = %u\n",
> > > > > +            fd, pid_magic, (unsigned) sizeof(req), NLM_F_DUMP,
> > > > > +            (unsigned) sizeof(req), (unsigned) sizeof(req));
> > > > 
> > > > I'd also add coverage for the following corner cases when
> > > > + data length equals to sizeof(struct nlmsghdr);
> > > > + data length is less than sizeof(struct nlmsghdr);
> > > > + data length is enough but data points to unmapped memory.
> > > > 
> > > I am not sure what you mean by "data".
> > 
> > By data I mean the 2nd argument of sendto, by data length I mean
> > the 3rd argument of sendto.
> > 
> > If only part of memory pointed by 2nd argument of sendto is mapped,
> > netlink parser won't be able to fetch it and is expected to print
> > something meaningfull.
> > 
> I really don't see how you can handle this case. Can I have any clue?

const void *const efault = tail_alloc(sizeof(struct nlmsghdr) - 1);
sendto(fd, efault, sizeof(struct nlmsghdr), ...


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