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ipv6: prevent infinite loop in rt6_nlmsg_size()

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While testing prior patch, I was able to trigger
an infinite loop in rt6_nlmsg_size() in the following place:

list_for_each_entry_rcu(sibling, &f6i->fib6_siblings,
			fib6_siblings) {
	rt6_nh_nlmsg_size(sibling->fib6_nh, &nexthop_len);
}

This is because fib6_del_route() and fib6_add_rt2node()
uses list_del_rcu(), which can confuse rcu readers,
because they might no longer see the head of the list.

Restart the loop if f6i->fib6_nsiblings is zero.

Fixes: d9ccb18f83 ("ipv6: Fix soft lockups in fib6_select_path under high next hop churn")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Link: https://patch.msgid.link/20250725140725.3626540-3-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
This commit is contained in:
Eric Dumazet
2025-07-26 11:31:00 -07:00
committed by Jakub Kicinski
parent ea2f921db7
commit 54e6fe9dd3
2 changed files with 22 additions and 20 deletions
Download Patch File Download Diff File Expand all files Collapse all files
net/ipv6/ip6_fib.c
+2 -2
View File
@@ -1265,7 +1265,7 @@ add:
&rt->fib6_siblings,
fib6_siblings)
sibling->fib6_nsiblings--;
rt->fib6_nsiblings = 0;
WRITE_ONCE(rt->fib6_nsiblings, 0);
list_del_rcu(&rt->fib6_siblings);
rcu_read_lock();
rt6_multipath_rebalance(next_sibling);
@@ -2015,7 +2015,7 @@ static void fib6_del_route(struct fib6_table *table, struct fib6_node *fn,
list_for_each_entry_safe(sibling, next_sibling,
&rt->fib6_siblings, fib6_siblings)
sibling->fib6_nsiblings--;
rt->fib6_nsiblings = 0;
WRITE_ONCE(rt->fib6_nsiblings, 0);
list_del_rcu(&rt->fib6_siblings);
rt6_multipath_rebalance(next_sibling);
}
net/ipv6/route.c
+20 -18
View File
@@ -5670,32 +5670,34 @@ static int rt6_nh_nlmsg_size(struct fib6_nh *nh, void *arg)
static size_t rt6_nlmsg_size(struct fib6_info *f6i)
{
struct fib6_info *sibling;
struct fib6_nh *nh;
int nexthop_len;
if (f6i->nh) {
nexthop_len = nla_total_size(4); /* RTA_NH_ID */
nexthop_for_each_fib6_nh(f6i->nh, rt6_nh_nlmsg_size,
&nexthop_len);
} else {
struct fib6_nh *nh = f6i->fib6_nh;
struct fib6_info *sibling;
nexthop_len = 0;
if (f6i->fib6_nsiblings) {
rt6_nh_nlmsg_size(nh, &nexthop_len);
rcu_read_lock();
list_for_each_entry_rcu(sibling, &f6i->fib6_siblings,
fib6_siblings) {
rt6_nh_nlmsg_size(sibling->fib6_nh, &nexthop_len);
}
rcu_read_unlock();
}
nexthop_len += lwtunnel_get_encap_size(nh->fib_nh_lws);
goto common;
}
rcu_read_lock();
retry:
nh = f6i->fib6_nh;
nexthop_len = 0;
if (READ_ONCE(f6i->fib6_nsiblings)) {
rt6_nh_nlmsg_size(nh, &nexthop_len);
list_for_each_entry_rcu(sibling, &f6i->fib6_siblings,
fib6_siblings) {
rt6_nh_nlmsg_size(sibling->fib6_nh, &nexthop_len);
if (!READ_ONCE(f6i->fib6_nsiblings))
goto retry;
}
}
rcu_read_unlock();
nexthop_len += lwtunnel_get_encap_size(nh->fib_nh_lws);
common:
return NLMSG_ALIGN(sizeof(struct rtmsg))
+ nla_total_size(16) /* RTA_SRC */
+ nla_total_size(16) /* RTA_DST */