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

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Date:   Sat, 21 Oct 2017 17:45:09 +0800
From:   Xin Long <lucien.xin@...il.com>
To:     Eric Dumazet <eric.dumazet@...il.com>
Cc:     Eric Dumazet <edumazet@...gle.com>,
        David Miller <davem@...emloft.net>,
        network dev <netdev@...r.kernel.org>,
        Marcelo Ricardo Leitner <marcelo.leitner@...il.com>,
        Sabrina Dubroca <sd@...asysnail.net>
Subject: Re: [PATCH net 0/2] net: diag: fix a potential security issue

On Sat, Oct 21, 2017 at 4:45 PM, Xin Long <lucien.xin@...il.com> wrote:
> On Sat, Oct 21, 2017 at 3:45 PM, Eric Dumazet <eric.dumazet@...il.com> wrote:
>> On Sat, 2017-10-21 at 14:51 +0800, Xin Long wrote:
>>> On Sat, Oct 21, 2017 at 2:18 PM, Eric Dumazet <edumazet@...gle.com> wrote:
>>> > On Fri, Oct 20, 2017 at 11:06 PM, Xin Long <lucien.xin@...il.com> wrote:
>>> >>
>>> >>
>>> >> On Sat, Oct 21, 2017 at 9:27 AM, David Miller <davem@...emloft.net> wrote:
>>> >>>
>>> >>> From: Xin Long <lucien.xin@...il.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).
>>
>> Your changelog mentions a security issue.
>>
>> How have you prevented user using socket() to bypass your 'security'
>> feature ?
> I think the hook in __sock_create():
>
>         err = security_socket_create(family, type, protocol, kern);
>         if (err)
>                 return err;
>
> could work for this, no ?
Sorry, Eric, this may not be an inappropriate example, after all
security_socket_create is not supposed to do these things.
thanks for your review.

Let's just see if David could accept the patches if I will
remove the "security claim" from changelog, considering
it as an improvement of sock diag.

David ?

>
> like, users add security rules to not allow to create SCTP socket
> (namely, not allow sctp module to be loaded)
>
> But, 'ss' could bypass it to load SCTP module.
>
> In this way, can this patch be considered a security issue ?
>
>>
>> If you have not yet, this security claim is simply false.