Re: [PATCH net 0/2] net: diag: fix a potential security issue

[Xin Long <lucien.xin@gmail.com>]

On Sat, Oct 21, 2017 at 2:18 PM, Eric Dumazet <edumazet@google.com> wrote:
> On Fri, Oct 20, 2017 at 11:06 PM, Xin Long <lucien.xin@gmail.com> wrote:
>>
>>
>> On Sat, Oct 21, 2017 at 9:27 AM, David Miller <davem@davemloft.net> wrote:
>>>
>>> From: Xin Long <lucien.xin@gmail.com>
>>> Date: Thu, 19 Oct 2017 15:32:23 +0800
>>>
>>> > This patch is to void the potential security issue that the family
>>> > or protocol modules are autoloaded when requesting _diag module by
>>> > not requesting _diag module if the family or protocol is not added
>>> > or registered in sock_diag and inet_diag.
>>> >
>>> > As the repost of the patch '[PATCH net] sock_diag: request _diag
>>> > module only when the family or proto has been registered', this
>>> > patchset fixes the compiling errors when INET is not set, and
>>> > also split into two patches to make it clear to review.
>>>
>>> This makes no sense to me.
>>>
>>> Any user can just open a socket() in the appropriate protocol
>>> family to cause the module to be loaded.
>>>
>>> If someone wants modules to not be loaded, block them using
>>> traditional module loading infrastructure mechanisms.  Or
>>> don't load the module at all.
>>>
>>> Sorry I am not applying this.
>>
>> Hi David,
>>
>> I'm still thinking it's not good after 'ss', sctp, dccp,
>> af_packet ... are just loaded, in which case, no one actually
>> open any socket with these family or proto.
>>
>> I talked with Marcelo before, one scenario as he said:
>>
>> Imagine a customer generates a sosreport on their system, and
>> with that, it loads sctp module. From then on, if their firewall
>> doesn't block incoming packets for sctp, they may be prone to some
>> remotely triggerable issue on sctp code, without even actually using
>> sctp.
>
> For that reason, we have disabled autoloading of SCTP.
> ( removing the
>  MODULE_ALIAS("net-pf-" __stringify(PF_INET) "-proto-132");
>  MODULE_ALIAS("net-pf-" __stringify(PF_INET6) "-proto-132");
> )
> root must modprobe the module before it is accessible.
>
> However inet_diag is a way to have the module loaded anyway.
>
> This is why I like your patch Xin.
>
> David is only saying that your patch alone is not enough to prevent a
> user to use socket() to autoload SCTP.
Using  socket() to autoload SCTP should be fine, cause users would
use SCTP, no ?

"ss" doesn't mean users intend to use SCTP, "ss" may make users
not aware that SCTP module would be loaded, unlike socket(SCTP).