linux-kernel - Re: [PATCH] ipv4: ipmr: add socket type checks to ipmr

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Message-ID: <CANn89iL5jS8BP+eXe1HeOBNpzfmVgTAHROGBK0qCAKJxvxUnuw@mail.gmail.com>
Date: Fri, 23 Jan 2026 10:26:51 +0100
From: Eric Dumazet <edumazet@...gle.com>
To: Suchit Karunakaran <suchitkarunakaran@...il.com>
Cc: davem@...emloft.net, dsahern@...nel.org, kuba@...nel.org, 
	pabeni@...hat.com, horms@...nel.org, netdev@...r.kernel.org, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] ipv4: ipmr: add socket type checks to ipmr_ioctl()

On Fri, Jan 23, 2026 at 10:04 AM Suchit Karunakaran
<suchitkarunakaran@...il.com> wrote:
>
> This is the IPv4 counterpart to commit ("ipv6: ip6mr: add socket type
> checks to ip6mr_ioctl()") [1].
>
> Similar to the IPv6 issue, ipmr_ioctl() and ipmr_compat_ioctl() access
> raw_sk(sk)->ipmr_table without first verifying that the socket is a raw
> socket with IPPROTO_IGMP protocol.
>
> This allows a permission bypass where a user with CAP_NET_RAW can create
> a non-IGMP raw socket (e.g., IPPROTO_UDP, IPPROTO_TCP, or any other
> protocol) and use SIOCGETVIFCNT or SIOCGETSGCNT ioctls to query IPv4
> multicast routing statistics. This bypasses the access control that
> restricts mroute operations to IGMP sockets only.

Where has this been documented? An RFC perhaps ?

This change could break applications if they were unaware of such rules.

I fail to see how querying statistics could be a risk.

What about the RTNL_FAMILY_IPMR rtnetlink interface ? I am sure it is
available to any user.