Re: [PATCH net] net: ping6: Fix possible leaked pernet namespace in pingv6_init()

[Kuniyuki Iwashima <kuniyu@amazon.com>]

From:   Chen Zhongjin <chenzhongjin@huawei.com>
Date:   Thu, 3 Nov 2022 17:03:45 +0800
> When IPv6 module initializing in pingv6_init(), inet6_register_protosw()
> is possible to fail but returns without any error cleanup.

The change itself looks sane, but how does it fail ?
It seems inet6_register_protosw() never fails for pingv6_protosw.
Am I missing something ?

---8<---
static struct inet_protosw pingv6_protosw = {
	.type =      SOCK_DGRAM,         <-- .type < SOCK_MAX
	.protocol =  IPPROTO_ICMPV6,
	.prot =      &pingv6_prot,
	.ops =       &inet6_sockraw_ops,
	.flags =     INET_PROTOSW_REUSE,  <-- always makes `answer` NULL
};

int inet6_register_protosw(struct inet_protosw *p)
{
	struct list_head *lh;
	struct inet_protosw *answer;
	struct list_head *last_perm;
	int protocol = p->protocol;
	int ret;

	spin_lock_bh(&inetsw6_lock);

	ret = -EINVAL;
	if (p->type >= SOCK_MAX)
		goto out_illegal;

	/* If we are trying to override a permanent protocol, bail. */
	answer = NULL;
	ret = -EPERM;
	last_perm = &inetsw6[p->type];
	list_for_each(lh, &inetsw6[p->type]) {
		answer = list_entry(lh, struct inet_protosw, list);

		/* Check only the non-wild match. */
		if (INET_PROTOSW_PERMANENT & answer->flags) {
			if (protocol == answer->protocol)
				break;
			last_perm = lh;
		}

		answer = NULL;
	}
	if (answer)
		goto out_permanent;
...
	list_add_rcu(&p->list, last_perm);
	ret = 0;
out:
	spin_unlock_bh(&inetsw6_lock);
	return ret;

out_permanent:
	pr_err("Attempt to override permanent protocol %d\n", protocol);
	goto out;

out_illegal:
	pr_err("Ignoring attempt to register invalid socket type %d\n",
	       p->type);
	goto out;
}
---8<---

> 
> This leaves wild ops in namespace list and when another module tries to
> add or delete pernet namespace it triggers page fault.
> Although IPv6 cannot be unloaded now, this error should still be handled
> to avoid kernel panic during IPv6 initialization.
> 
> BUG: unable to handle page fault for address: fffffbfff80bab69
> CPU: 0 PID: 434 Comm: modprobe
> RIP: 0010:unregister_pernet_operations+0xc9/0x450
> Call Trace:
>  <TASK>
>  unregister_pernet_subsys+0x31/0x3e
>  nf_tables_module_exit+0x44/0x6a [nf_tables]
>  __do_sys_delete_module.constprop.0+0x34f/0x5b0
>  ...
> 
> Fix it by adding error handling in pingv6_init(), and add a helper

I'm wondering this could be another place.


> function pingv6_ops_unset to avoid duplicate code.
> 
> Fixes: d862e5461423 ("net: ipv6: Implement /proc/net/icmp6.")
> Signed-off-by: Chen Zhongjin <chenzhongjin@huawei.com>
> ---
>  net/ipv6/ping.c | 30 ++++++++++++++++++++++--------
>  1 file changed, 22 insertions(+), 8 deletions(-)
> 
> diff --git a/net/ipv6/ping.c b/net/ipv6/ping.c
> index 86c26e48d065..5df688dd5208 100644
> --- a/net/ipv6/ping.c
> +++ b/net/ipv6/ping.c
> @@ -277,10 +277,21 @@ static struct pernet_operations ping_v6_net_ops = {
>  };
>  #endif
>  
> +static void pingv6_ops_unset(void)
> +{
> +	pingv6_ops.ipv6_recv_error = dummy_ipv6_recv_error;
> +	pingv6_ops.ip6_datagram_recv_common_ctl = dummy_ip6_datagram_recv_ctl;
> +	pingv6_ops.ip6_datagram_recv_specific_ctl = dummy_ip6_datagram_recv_ctl;
> +	pingv6_ops.icmpv6_err_convert = dummy_icmpv6_err_convert;
> +	pingv6_ops.ipv6_icmp_error = dummy_ipv6_icmp_error;
> +	pingv6_ops.ipv6_chk_addr = dummy_ipv6_chk_addr;
> +}
> +
>  int __init pingv6_init(void)
>  {
> +	int ret;
>  #ifdef CONFIG_PROC_FS
> -	int ret = register_pernet_subsys(&ping_v6_net_ops);
> +	ret = register_pernet_subsys(&ping_v6_net_ops);
>  	if (ret)
>  		return ret;
>  #endif
> @@ -291,7 +302,15 @@ int __init pingv6_init(void)
>  	pingv6_ops.icmpv6_err_convert = icmpv6_err_convert;
>  	pingv6_ops.ipv6_icmp_error = ipv6_icmp_error;
>  	pingv6_ops.ipv6_chk_addr = ipv6_chk_addr;
> -	return inet6_register_protosw(&pingv6_protosw);
> +
> +	ret = inet6_register_protosw(&pingv6_protosw);
> +	if (ret) {
> +		pingv6_ops_unset();
> +#ifdef CONFIG_PROC_FS
> +		unregister_pernet_subsys(&ping_v6_net_ops);
> +#endif
> +	}
> +	return ret;
>  }
>  
>  /* This never gets called because it's not possible to unload the ipv6 module,
> @@ -299,12 +318,7 @@ int __init pingv6_init(void)
>   */
>  void pingv6_exit(void)
>  {
> -	pingv6_ops.ipv6_recv_error = dummy_ipv6_recv_error;
> -	pingv6_ops.ip6_datagram_recv_common_ctl = dummy_ip6_datagram_recv_ctl;
> -	pingv6_ops.ip6_datagram_recv_specific_ctl = dummy_ip6_datagram_recv_ctl;
> -	pingv6_ops.icmpv6_err_convert = dummy_icmpv6_err_convert;
> -	pingv6_ops.ipv6_icmp_error = dummy_ipv6_icmp_error;
> -	pingv6_ops.ipv6_chk_addr = dummy_ipv6_chk_addr;
> +	pingv6_ops_unset();
>  #ifdef CONFIG_PROC_FS
>  	unregister_pernet_subsys(&ping_v6_net_ops);
>  #endif
> -- 
> 2.17.1