On 1/22/17 9:58 PM, David Miller wrote:
>
> David, please slow down.
>
> How is the NULL entry getting selected to be dumped and passed
> down here in the first place?
The null_entry might be a 'marker' but is integral to the ipv6 fib. For
starters:
static int __net_init fib6_net_init(struct net *net)
{
...
net->ipv6.fib6_main_tbl = kzalloc(sizeof(*net->ipv6.fib6_main_tbl),
GFP_KERNEL);
...
net->ipv6.fib6_main_tbl->tb6_id = RT6_TABLE_MAIN;
net->ipv6.fib6_main_tbl->tb6_root.leaf = net->ipv6.ip6_null_entry;
...
Same goes for every other table allocated:
static struct fib6_table *fib6_alloc_table(struct net *net, u32 id)
{
struct fib6_table *table;
table = kzalloc(sizeof(*table), GFP_ATOMIC);
if (table) {
table->tb6_id = id;
table->tb6_root.leaf = net->ipv6.ip6_null_entry;
..
}
And if you look at the fib6_add code:
sfn->leaf = info->nl_net->ipv6.ip6_null_entry;
atomic_inc(&info->nl_net->ipv6.ip6_null_entry->rt6i_ref);
sfn->fn_flags = RTN_ROOT;
sfn->fn_sernum = sernum;
/* Now add the first leaf node to new subtree */
sn = fib6_add_1(sfn, &rt->rt6i_src.addr,
rt->rt6i_src.plen,
offsetof(struct rt6_info, rt6i_src),
allow_create, replace_required, sernum);
Meaning that a walk of the table is going to dump the ip6_null_entry route,
potentially multiple times.
As far as the dump request the chain rtnetlink message invokes inet6_dump_fib:
inet6_dump_fib
- fib6_dump_table
+ fib6_walk
* fib6_walk_continue
- fib6_dump_node
+ rt6_dump_route
Seems to me the most appropriate place to check that rt is the null_entry route
is rt6_dump_route but perhaps fib6_dump_node could as well. This patch buts the
check in rt6_dump_route.
