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

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Date:   Sat, 21 Oct 2017 00:45:55 -0700
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Xin Long <lucien.xin@...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, 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 ?

If you have not yet, this security claim is simply false.