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

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

[Yuyang Huang]

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@vger.kernel.org
Signed-off-by: Yuyang Huang <yuyanghuang@google.com>
---
v3:
  - Target 'net' instead of 'net-next'.
  - Add the KASAN Use-After-Free traceback to the commit message.
v2:
  - Add Fixes tag in the commit message.

 net/ipv4/igmp.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/net/ipv4/igmp.c b/net/ipv4/igmp.c
index b6337a47c141..d520ea4f6d14 100644
--- a/net/ipv4/igmp.c
+++ b/net/ipv4/igmp.c
@@ -1922,6 +1922,7 @@ void ip_mc_destroy_dev(struct in_device *in_dev)
 #endif
 
 	while ((i = rtnl_dereference(in_dev->mc_list)) != NULL) {
+		ip_mc_hash_remove(in_dev, i);
 		in_dev->mc_list = i->next_rcu;
 		WRITE_ONCE(in_dev->mc_count, in_dev->mc_count - 1);
 		ip_mc_clear_src(i);
-- 
2.55.0.rc0.799.gd6f94ed593-goog

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

[Kuniyuki Iwashima]

From: Yuyang Huang <yuyanghuang@google.com>
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@vger.kernel.org
> Signed-off-by: Yuyang Huang <yuyanghuang@google.com>

Reviewed-by: Kuniyuki Iwashima <kuniyu@google.com>

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

[Ido Schimmel]

On Thu, Jul 02, 2026 at 08:50:14AM +0900, Yuyang Huang wrote:
> 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.

[...]

> 
> Fixes: e9897071350b ("igmp: hash a hash table to speedup ip_check_mc_rcu()")
> Cc: stable@vger.kernel.org
> Signed-off-by: Yuyang Huang <yuyanghuang@google.com>

Reviewed-by: Ido Schimmel <idosch@nvidia.com>