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Message-ID: <7492d260-0e17-4f60-81c2-861efe317ece@huawei.com>
Date: Wed, 23 Oct 2024 14:52:00 +0800
From: "dongchenchen (A)" <dongchenchen2@...wei.com>
To: <dongchenchen2@...wei.com>
CC: <pablo@...filter.org>, <kadlec@...filter.org>, <davem@...emloft.net>,
<edumazet@...gle.com>, <kuba@...nel.org>, <pabeni@...hat.com>,
<fw@...len.de>, <kuniyu@...zon.com>, <netfilter-devel@...r.kernel.org>,
<netdev@...r.kernel.org>, <yuehaibing@...wei.com>, Simon Horman
<horms@...nel.org>
Subject: Re: [PATCH net] net: netfilter: Fix use-after-free in get_info()
On 2024/10/23 14:32, dongchenchen (A) wrote:
>
> On 2024/10/22 23:33, Simon Horman wrote:
>> On Tue, Oct 22, 2024 at 04:57:53PM +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
>>> //remove table 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. Skip
>>> the re-traversal of xt_net->tables list to fix it.
>>>
>>> Fixes: c22921df777d ("netfilter: iptables: Fix potential
>>> null-ptr-deref in ip6table_nat_table_init().")
>>> Signed-off-by: Dong Chenchen <dongchenchen2@...wei.com>
>>> ---
>>> net/netfilter/x_tables.c | 8 +++++---
>>> 1 file changed, 5 insertions(+), 3 deletions(-)
>>>
>>> diff --git a/net/netfilter/x_tables.c b/net/netfilter/x_tables.c
>>> index da5d929c7c85..359c880ecb07 100644
>>> --- a/net/netfilter/x_tables.c
>>> +++ b/net/netfilter/x_tables.c
>>> @@ -1239,6 +1239,7 @@ struct xt_table *xt_find_table_lock(struct net
>>> *net, u_int8_t af,
>>> struct module *owner = NULL;
>>> struct xt_template *tmpl;
>>> struct xt_table *t;
>>> + int err = -ENOENT;
>>> mutex_lock(&xt[af].mutex);
>>> list_for_each_entry(t, &xt_net->tables[af], list)
>>> @@ -1247,8 +1248,6 @@ struct xt_table *xt_find_table_lock(struct net
>>> *net, u_int8_t af,
>>> /* Table doesn't exist in this netns, check larval list */
>>> list_for_each_entry(tmpl, &xt_templates[af], list) {
>>> - int err;
>>> -
>>> if (strcmp(tmpl->name, name))
>>> continue;
>>> if (!try_module_get(tmpl->me))
>>> @@ -1267,6 +1266,9 @@ struct xt_table *xt_find_table_lock(struct net
>>> *net, u_int8_t af,
>>> break;
>>> }
>>> + if (err < 0)
>>> + goto out;
>>> +
>>> /* and once again: */
>>> list_for_each_entry(t, &xt_net->tables[af], list)
>>> if (strcmp(t->name, name) == 0)
>>> @@ -1275,7 +1277,7 @@ struct xt_table *xt_find_table_lock(struct net
>>> *net, u_int8_t af,
>>> module_put(owner);
>> Hi Dong Chenchen,
>>
>> I'm unsure if this can happen in practice, although I guess so else the
>> module_put() call above is never reached.
>
> Hi, Simon. Thank you very much for your suggestions!
>
> module_put(owner) will be never reached indeed. which wiil be executed
> in:
>
>
sorry, there is a problem with the email format. resend:
module_put(owner) wiil be executed in:
1. xt_table not found in tmpl list and xt_net list:
owner == NULL, no need to put
2. xt_table found in tmpl list, table_init() fail to add table to xt_net
list but return 0
this situation may be mutually exclusive
So I thought it may not need to call module_puy(owner) here
xt_find_table_lock
list_for_each_entry(tmpl, &xt_templates[af], list)
if (strcmp(tmpl->name, name))
continue;
err = tmpl->table_init(net); //add xtable to xt_net list
if (err < 0) {
module_put(owner);
return ERR_PTR(err);
}
list_for_each_entry(t, &xt_net->tables[af], list)
if (strcmp(t->name, name) == 0)
return t; //err = 0, will return here
module_put(owner); // put effectively while (err == 0) && (xtable
found in tmpl list) and add table xt_net list failed in table_init()
out:
mutex_unlock(&xt[af].mutex);
return ERR_PTR(-ENOENT);
>> In any case, previously if we got
>> to this line then the function would return ERR_PTR(-ENOENT). But now it
>> will return ERR_PTR(0). Which although valid often indicates a bug.
>>
>> Flagged by Smatch.
>
> As described above, err = 0 will be return in xt_net table list re-
> traversal.
>
>>> out:
>>> mutex_unlock(&xt[af].mutex);
>>> - return ERR_PTR(-ENOENT);
>>> + return ERR_PTR(err);
>>> }
>>> EXPORT_SYMBOL_GPL(xt_find_table_lock);
>>> --
>>> 2.25.1
>>>
>>>
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