ipv6: check fn->leaf before it is used
If rwlock is replaced with rcu and spinlock, it is possible that the
reader thread will see fn->leaf as NULL in the following scenarios:
1. fib6_add() is in progress and we have already inserted a new node but
not yet inserted the route.
2. fib6_del_route() is in progress and we have already set fn->leaf to
NULL but not yet freed the node because of rcu grace period.
This patch makes sure all the reader threads check fn->leaf first before
using it. And together with later patch to grab rcu_read_lock() and
rcu_dereference() fn->leaf, it makes sure reader threads are safe when
accessing fn->leaf.
Signed-off-by: Wei Wang <weiwan@google.com>
Signed-off-by: Martin KaFai Lau <kafai@fb.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/ipv6/route.c b/net/ipv6/route.c
index aeb349a..05dc450 100644
--- a/net/ipv6/route.c
+++ b/net/ipv6/route.c
@@ -712,6 +712,7 @@ static struct rt6_info *find_match(struct rt6_info *rt, int oif, int strict,
}
static struct rt6_info *find_rr_leaf(struct fib6_node *fn,
+ struct rt6_info *leaf,
struct rt6_info *rr_head,
u32 metric, int oif, int strict,
bool *do_rr)
@@ -730,7 +731,7 @@ static struct rt6_info *find_rr_leaf(struct fib6_node *fn,
match = find_match(rt, oif, strict, &mpri, match, do_rr);
}
- for (rt = fn->leaf; rt && rt != rr_head; rt = rt->dst.rt6_next) {
+ for (rt = leaf; rt && rt != rr_head; rt = rt->dst.rt6_next) {
if (rt->rt6i_metric != metric) {
cont = rt;
break;
@@ -748,17 +749,21 @@ static struct rt6_info *find_rr_leaf(struct fib6_node *fn,
return match;
}
-static struct rt6_info *rt6_select(struct fib6_node *fn, int oif, int strict)
+static struct rt6_info *rt6_select(struct net *net, struct fib6_node *fn,
+ int oif, int strict)
{
+ struct rt6_info *leaf = fn->leaf;
struct rt6_info *match, *rt0;
- struct net *net;
bool do_rr = false;
+ if (!leaf)
+ return net->ipv6.ip6_null_entry;
+
rt0 = fn->rr_ptr;
if (!rt0)
- fn->rr_ptr = rt0 = fn->leaf;
+ fn->rr_ptr = rt0 = leaf;
- match = find_rr_leaf(fn, rt0, rt0->rt6i_metric, oif, strict,
+ match = find_rr_leaf(fn, leaf, rt0, rt0->rt6i_metric, oif, strict,
&do_rr);
if (do_rr) {
@@ -766,13 +771,12 @@ static struct rt6_info *rt6_select(struct fib6_node *fn, int oif, int strict)
/* no entries matched; do round-robin */
if (!next || next->rt6i_metric != rt0->rt6i_metric)
- next = fn->leaf;
+ next = leaf;
if (next != rt0)
fn->rr_ptr = next;
}
- net = dev_net(rt0->dst.dev);
return match ? match : net->ipv6.ip6_null_entry;
}
@@ -1623,7 +1627,7 @@ struct rt6_info *ip6_pol_route(struct net *net, struct fib6_table *table,
oif = 0;
redo_rt6_select:
- rt = rt6_select(fn, oif, strict);
+ rt = rt6_select(net, fn, oif, strict);
if (rt->rt6i_nsiblings)
rt = rt6_multipath_select(rt, fl6, oif, strict);
if (rt == net->ipv6.ip6_null_entry) {