CVE-2026-98099ipv6: mcast: use rcu_assign_pointer() for __rcu list updates

Official description

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().

Affected packages & fixed versions

Affected products (as reported)

References

• https://git.kernel.org/stable/c/0e3e3cec28c4d1bf29948da40b4e9e5d44f7852b
• https://git.kernel.org/stable/c/49d7e1b456ba2f3ee08b3e264d999c09992cde8e
• https://git.kernel.org/stable/c/afca229b39acc2590976b3e4f6e0fe76cededc60
• https://git.kernel.org/stable/c/2e46b0c9fcf7e10b64ce1630b925f47918d1f7f6
• https://git.kernel.org/stable/c/0c8f56c583c3250408367880c98e4d6fbc929315