Re: [PATCH net v2] net: netfilter: Fix use-after-free in get_info()

[Pablo Neira Ayuso <pablo@netfilter.org>]

On Thu, Oct 24, 2024 at 09:47:01AM +0800, Dong Chenchen wrote:
> ip6table_nat module unload has refcnt warning for UAF. call trace is:
> 
> WARNING: CPU: 1 PID: 379 at kernel/module/main.c:853 module_put+0x6f/0x80
> Modules linked in: ip6table_nat(-)
> CPU: 1 UID: 0 PID: 379 Comm: ip6tables Not tainted 6.12.0-rc4-00047-gc2ee9f594da8-dirty #205
> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996),
> BIOS rel-1.13.0-0-gf21b5a4aeb02-prebuilt.qemu.org 04/01/2014
> RIP: 0010:module_put+0x6f/0x80
> Call Trace:
>  <TASK>
>  get_info+0x128/0x180
>  do_ip6t_get_ctl+0x6a/0x430
>  nf_getsockopt+0x46/0x80
>  ipv6_getsockopt+0xb9/0x100
>  rawv6_getsockopt+0x42/0x190
>  do_sock_getsockopt+0xaa/0x180
>  __sys_getsockopt+0x70/0xc0
>  __x64_sys_getsockopt+0x20/0x30
>  do_syscall_64+0xa2/0x1a0
>  entry_SYSCALL_64_after_hwframe+0x77/0x7f
> 
> Concurrent execution of module unload and get_info() trigered the warning.
> The root cause is as follows:
> 
> cpu0				      cpu1
> module_exit
> //mod->state = MODULE_STATE_GOING
>   ip6table_nat_exit
>     xt_unregister_template
> 	kfree(t)
> 	//removed from templ_list
> 				      getinfo()
> 					  t = xt_find_table_lock
> 						list_for_each_entry(tmpl, &xt_templates[af]...)
> 							if (strcmp(tmpl->name, name))
> 								continue;  //table not found
> 							try_module_get
> 						list_for_each_entry(t, &xt_net->tables[af]...)
> 							return t;  //not get refcnt
> 					  module_put(t->me) //uaf
>     unregister_pernet_subsys
>     //remove table from xt_net list
> 
> While xt_table module was going away and has been removed from
> xt_templates list, we couldnt get refcnt of xt_table->me. Check
> module in xt_net->tables list re-traversal to fix it.

Applied, thanks