Re: [PATCH net-next v2] ipv4: igmp: remove multicast group from hash table on device destruction

[Kuniyuki Iwashima]

From: Ido Schimmel <idosch@xxxxxxxxxx>
Date: Tue, 30 Jun 2026 19:59:34 +0300
> On Tue, Jun 30, 2026 at 04:55:22PM +0900, Yuyang Huang wrote:
> > > Hi,
> > >
> > > why sending this to net-next not to net if that's a bug fix?
> > >
> > > In the v1 thread it was said
> > > >This is a long-standing bug, not a recent regression.
> > >
> > > so why do not cc stable kernel to get rid of this bug from
> > > stable kernels in such case?
> > 
> > Thanks for the advise, will send this patch to stable kernel.
> 
> Please target v3 at net and add a trace given you're claiming for a
> use-after-free. That way we know that the problem is real and not a
> false-positive from some tool. You can reproduce it by adding enough
> delay in inetdev_destroy():

I guess delay was added between ip_mc_destroy_dev() and
RCU_INIT_POINTER(dev->ip_ptr, NULL) ?

I feel like we should clear it first and destroy everything
as done in IPv6 addrconf_ifdown().


> 
> BUG: KASAN: slab-use-after-free in ip_check_mc_rcu+0x2cc/0x500
> Read of size 4 at addr ffff88810c571208 by task mausezahn/419
> 
> CPU: 2 UID: 0 PID: 419 Comm: mausezahn Not tainted 7.1.0-virtme-g15d4a7c23bf6 #17 PREEMPT(lazy)
> Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011
> Call Trace:
>  <IRQ>
>  dump_stack_lvl+0x4d/0x70
>  print_report+0x153/0x4c2
>  kasan_report+0xda/0x110
>  ip_check_mc_rcu+0x2cc/0x500
>  ip_route_input_rcu.part.0+0x13d/0xbc0
>  ip_route_input_noref+0xb6/0x110
>  ip_rcv_finish_core+0x41b/0x1d90
>  ip_rcv_finish+0xea/0x1b0
>  ip_rcv+0xb7/0x1b0
>  __netif_receive_skb_one_core+0xfc/0x180
>  process_backlog+0x1ea/0x5e0
>  __napi_poll+0x97/0x480
>  net_rx_action+0x97c/0xfa0
>  handle_softirqs+0x18c/0x4f0
>  do_softirq+0x42/0x60
>  </IRQ>
>