CVE-2026-64423

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

ipv4: igmp: remove multicast group from hash table on device destruction

When a device is destroyed under RTNL, ip_mc_destroy_dev() iterates through

the multicast list and calls ip_ma_put() on each membership, scheduling

them for RCU reclamation. However, they are not unlinked from the device's

multicast hash table (mc_hash).

Since the device remains published in dev->ip_ptr until after

ip_mc_destroy_dev() completes, concurrent RCU readers traversing mc_hash

can still locate and access the multicast group after its refcount is

decremented. If the RCU callback runs and frees the group while a reader is

accessing it, a use-after-free occurs.

Fix this by unlinking the multicast group from mc_hash using

ip_mc_hash_remove() before scheduling it for reclamation.

BUG: KASAN: slab-use-after-free in ip_check_mc_rcu+0x149/0x3f0

Read of size 4 at addr ffff888009bf1408 by task mausezahn/2276

Call Trace:

<IRQ>

dump_stack_lvl+0x67/0x90

print_report+0x175/0x7c0

kasan_report+0x147/0x180

ip_check_mc_rcu+0x149/0x3f0

udp_v4_early_demux+0x36d/0x12d0

ip_rcv_finish_core+0xb8b/0x1390

ip_rcv_finish+0x54/0x120

NF_HOOK+0x213/0x2b0

__netif_receive_skb+0x126/0x340

process_backlog+0x4f2/0xf00

__napi_poll+0x92/0x2c0

net_rx_action+0x583/0xc60

handle_softirqs+0x236/0x7f0

do_softirq+0x57/0x80

</IRQ>

Allocated by task 2239:

kasan_save_track+0x3e/0x80

__kasan_kmalloc+0x72/0x90

____ip_mc_inc_group+0x31a/0xa40

__ip_mc_join_group+0x334/0x3f0

do_ip_setsockopt+0x16fa/0x2010

ip_setsockopt+0x3f/0x90

do_sock_setsockopt+0x1ad/0x300

Freed by task 0:

kasan_save_track+0x3e/0x80

kasan_save_free_info+0x40/0x50

__kasan_slab_free+0x3a/0x60

__rcu_free_sheaf_prepare+0xd4/0x220

rcu_free_sheaf+0x36/0x190

rcu_core+0x8d9/0x12f0

handle_softirqs+0x236/0x7f0