Re: [PATCH net v3] ipv4: igmp: remove multicast group from hash table on device destruction

[Kuniyuki Iwashima]

From: Yuyang Huang <yuyanghuang@xxxxxxxxxx>
Date: Thu,  2 Jul 2026 08:50:14 +0900
> 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
> 
> Fixes: e9897071350b ("igmp: hash a hash table to speedup ip_check_mc_rcu()")
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Yuyang Huang <yuyanghuang@xxxxxxxxxx>

Reviewed-by: Kuniyuki Iwashima <kuniyu@xxxxxxxxxx>