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

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Message-ID: <CAO9wTFhNijfEbmASx8rdStWSjvQicCvA5nSHqF4B4XpNxu0nGg@mail.gmail.com>
Date: Sat, 24 Jan 2026 20:55:35 +0530
From: Suchit Karunakaran <suchitkarunakaran@...il.com>
To: Eric Dumazet <edumazet@...gle.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, 23 Jan 2026 at 14:57, Eric Dumazet <edumazet@...gle.com> wrote:
>
> 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.

Hi Eric. The primary motivations for this patch are the IPv6
counterpart mentioned in the commit message and the commit 5e1859f.