CVE-2026-98099

In the Linux kernel, the following vulnerability has been resolved:

ipv6: mcast: use rcu_assign_pointer() for __rcu list updates

Several places in net/ipv6/mcast.c update RCU-protected lists

(np->ipv6_mc_list, idev->mc_list, idev->mc_tomb) using direct pointer

assignments instead of rcu_assign_pointer():

1. In __ipv6_dev_mc_dec(), unlinking a group from idev->mc_list did:

*map = ma->next;

without rcu_assign_pointer() while concurrent readers traverse

idev->mc_list locklessly under rcu_read_lock().

2. In ipv6_sock_mc_drop() and __ipv6_sock_mc_close(), unlinking a group

from np->ipv6_mc_list directly assigned *lnk = mc_lst->next and

np->ipv6_mc_list = mc_lst->next without rcu_assign_pointer(), racing

with lockless readers in inet6_mc_check().

3. In __ipv6_sock_mc_join(), mc_lst->next was initialized to

np->ipv6_mc_list via raw assignment before publishing mc_lst.

4. In mld_del_delrec() and __ipv6_dev_mc_inc(), __rcu source pointers

passed into rcu_assign_pointer() lacked explicit dereference helpers.

Fix these by consistently using rcu_assign_pointer() along with

mc_dereference() / sock_dereference().