Re: [PATCH] Fix Warnings from net/netlink/genetlink.c

[Stephen Rothwell <sfr@xxxxxxxxxxxxxxxx>]

Hi all,

On Tue, 11 Aug 2009 20:24:59 -0700 Stephen Hemminger <shemminger@xxxxxxxxxx> wrote:
>
> > > @@ -136,7 +136,7 @@ int genl_register_mc_group(struct genl_family *family,
> > >  {
> > >         int id;
> > >         unsigned long *new_groups;
> > > -       int err;
> > > +       int err = 0;
> > >  
> > >         BUG_ON(grp->name[0] == '\0');
> > 
> > this looks fishy. How does gcc thinks this variable is uninitialized. If
> > I look at the code in Linus' tree, I don't see it.
> 
> Agreed, and the line numbers are off.

In the -next tree, it looks like this:

int genl_register_mc_group(struct genl_family *family,
			   struct genl_multicast_group *grp)
{
	int id;
	unsigned long *new_groups;
	int err;

	BUG_ON(grp->name[0] == '\0');

	genl_lock();

	/* special-case our own group */
	if (grp == &notify_grp)
		id = GENL_ID_CTRL;
	else
		id = find_first_zero_bit(mc_groups,
					 mc_groups_longs * BITS_PER_LONG);


	if (id >= mc_groups_longs * BITS_PER_LONG) {
		size_t nlen = (mc_groups_longs + 1) * sizeof(unsigned long);

		if (mc_groups == &mc_group_start) {
			new_groups = kzalloc(nlen, GFP_KERNEL);
			if (!new_groups) {
				err = -ENOMEM;
				goto out;
			}
			mc_groups = new_groups;
			*mc_groups = mc_group_start;
		} else {
			new_groups = krealloc(mc_groups, nlen, GFP_KERNEL);
			if (!new_groups) {
				err = -ENOMEM;
				goto out;
			}
			mc_groups = new_groups;
			mc_groups[mc_groups_longs] = 0;
		}
		mc_groups_longs++;
	}

	if (family->netnsok) {
		struct net *net;

		rcu_read_lock();
		for_each_net_rcu(net) {
			err = netlink_change_ngroups(net->genl_sock,
					mc_groups_longs * BITS_PER_LONG);
			if (err) {
				rcu_read_unlock();
				goto out;
			}
		}
		rcu_read_unlock();
	} else {
		err = netlink_change_ngroups(init_net.genl_sock,
					     mc_groups_longs * BITS_PER_LONG);
		if (err)
			goto out;
	}

	grp->id = id;
	set_bit(id, mc_groups);
	list_add_tail(&grp->list, &family->mcast_groups);
	grp->family = family;

	genl_ctrl_event(CTRL_CMD_NEWMCAST_GRP, grp);
 out:
	genl_unlock();
	return err;
}

so if family->netnsok is true and the for_each_net_rcu loop executes 0
times, err will not be set ...  Now, that may not be logically possible,
but I can't tell that from this code.

-- 
Cheers,
Stephen Rothwell                    sfr@xxxxxxxxxxxxxxxx
http://www.canb.auug.org.au/~sfr/

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