From: bluhm <bluhm@openbsd.org>
Date: Thu, 11 Apr 2024 15:08:18 +0000 (+0000)
Subject: Prevent changing interface loopback flag from userland.
X-Git-Url: http://artulab.com/gitweb/?a=commitdiff_plain;h=4733ced31b52279ffbbb7a95a03079ab09f79d05;p=openbsd

Prevent changing interface loopback flag from userland.

IFF_LOOPBACK is telling userland the behaviour of a specific driver,
it is supposed to be static and permanent.  Clearing the loopback
flag on lo0 could lead to a kernel crash due to inconsistent multicast
igmp group.

Reported-by: syzbot+2f24ed6c8ddb2d6bb22c@syzkaller.appspotmail.com
OK claudio@ deraadt@
---

diff --git a/sys/net/if.h b/sys/net/if.h
index c32a15ed0e9..ae50958ee5a 100644
--- a/sys/net/if.h
+++ b/sys/net/if.h
@@ -1,4 +1,4 @@
-/*	$OpenBSD: if.h,v 1.215 2023/11/11 14:24:03 bluhm Exp $	*/
+/*	$OpenBSD: if.h,v 1.216 2024/04/11 15:08:18 bluhm Exp $	*/
 /*	$NetBSD: if.h,v 1.23 1996/05/07 02:40:27 thorpej Exp $	*/
 
 /*
@@ -219,7 +219,7 @@ struct if_status_description {
 
 /* flags set internally only: */
 #define	IFF_CANTCHANGE \
-	(IFF_BROADCAST|IFF_POINTOPOINT|IFF_RUNNING|IFF_OACTIVE|\
+	(IFF_BROADCAST|IFF_LOOPBACK|IFF_POINTOPOINT|IFF_RUNNING|IFF_OACTIVE|\
 	    IFF_SIMPLEX|IFF_MULTICAST|IFF_ALLMULTI)
 
 #define	IFXF_MPSAFE		0x1	/* [I] if_start is mpsafe */