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Date: Wed, 7 Jul 2021 11:18:07 +0200
From: Pablo Neira Ayuso <pablo@...filter.org>
To: iLifetruth <yixiaonn@...il.com>
Cc: Jozsef Kadlecsik <kadlec@...filter.org>,
Florian Westphal <fw@...len.de>,
"David S. Miller" <davem@...emloft.net>,
Jakub Kicinski <kuba@...nel.org>,
netfilter-devel@...r.kernel.org, coreteam@...filter.org,
netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
Qiang Liu <cyruscyliu@...il.com>, yajin@...kernel.org
Subject: Re: netfilter: Use netlink_ns_capable to verify the permisions of
netlink messages
On Wed, Jul 07, 2021 at 04:05:33PM +0800, iLifetruth wrote:
> Hi, we have found that the same fix pattern of CVE-2014-0181 may not
> forward ported to some netlink-related places in the latest linux
> kernel(v5.13)
>
> =============
> Here is the description of CVE-2014-0181:
>
> The Netlink implementation in the Linux kernel through 3.14.1 does not
> provide a mechanism for authorizing socket operations based on the opener
> of a socket, which allows local users to bypass intended access
> restrictions and modify network configurations by using a Netlink socket
> for the (1) stdout or (2) stderr of a setuid program.
>
> ==========
> And here is the solution to CVE-2014-0181:
>
> To keep this from happening, replace bare capable and ns_capable calls with
> netlink_capable, netlink_net_calls and netlink_ns_capable calls. Which act
> the same as the previous calls *except they verify that the opener of the
> socket had the desired permissions as well.*
>
> ==========
> The upstream patch commit of this vulnerability described in CVE-2014-0181
> is:
> 90f62cf30a78721641e08737bda787552428061e (committed about 7 years ago)
>
> =========
> Capable() checks were added to these netlink-related places listed below
> in netfilter by another upstream commit:
> 4b380c42f7d00a395feede754f0bc2292eebe6e5(committed about 4 years ago)
>
> In kernel v5.13:
> File_1: linux/net/netfilter/nfnetlink_cthelper.c
> in line 424, line 623 and line 691
> File_2: linux/net/netfilter/nfnetlink_osf.c
> in line 305 and line 351
These subsystems depend on nfnetlink.
nfnetlink_rcv() is called before passing the message to the
corresponding backend, e.g. nfnetlink_osf.
static void nfnetlink_rcv(struct sk_buff *skb)
{
struct nlmsghdr *nlh = nlmsg_hdr(skb);
if (skb->len < NLMSG_HDRLEN ||
nlh->nlmsg_len < NLMSG_HDRLEN ||
skb->len < nlh->nlmsg_len)
return;
if (!netlink_net_capable(skb, CAP_NET_ADMIN)) {
netlink_ack(skb, nlh, -EPERM, NULL);
return;
}
[...]
which is calling netlink_net_capable().
> But these checkers are still using bare capable instead of netlink_capable
> calls. So this is likely to trigger the vulnerability described in the
> CVE-2014-0181 without checking the desired permissions of the socket
> opener. Now, shall we forward port the fix pattern from the patch of
> CVE-2014-0181?
>
> We would like to contact you to confirm this problem.
I think these capable() calls in nfnetlink_cthelper and nfnetlink_osf
are dead code that can be removed. As I explained these subsystems
stay behind nfnetlink.
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