Merge: vlan: enforce underlying device type

MR: https://gitlab.com/redhat/centos-stream/src/kernel/centos-stream-9/-/merge_requests/6871

JIRA: https://issues.redhat.com/browse/RHEL-87883
Upstream Status: linux.git
CVE: CVE-2025-21920

commit b33a534
Author: Oscar Maes <oscmaes92@gmail.com>
Date:   Mon Mar 3 16:56:19 2025 +0100

    vlan: enforce underlying device type

    Currently, VLAN devices can be created on top of non-ethernet devices.

    Besides the fact that it doesn't make much sense, this also causes a
    bug which leaks the address of a kernel function to usermode.

    When creating a VLAN device, we initialize GARP (garp_init_applicant)
    and MRP (mrp_init_applicant) for the underlying device.

    As part of the initialization process, we add the multicast address of
    each applicant to the underlying device, by calling dev_mc_add.

    __dev_mc_add uses dev->addr_len to determine the length of the new
    multicast address.

    This causes an out-of-bounds read if dev->addr_len is greater than 6,
    since the multicast addresses provided by GARP and MRP are only 6
    bytes long.

    This behaviour can be reproduced using the following commands:

    ip tunnel add gretest mode ip6gre local ::1 remote ::2 dev lo
    ip l set up dev gretest
    ip link add link gretest name vlantest type vlan id 100

    Then, the following command will display the address of garp_pdu_rcv:

    ip maddr show | grep 01:80:c2:00:00:21

    Fix the bug by enforcing the type of the underlying device during VLAN
    device initialization.

    Fixes: 22bedad ("net: convert multicast list to list_head")
    Reported-by: syzbot+91161fe81857b396c8a0@syzkaller.appspotmail.com
    Closes: https://lore.kernel.org/netdev/000000000000ca9a81061a01ec20@google.com/
    Signed-off-by: Oscar Maes <oscmaes92@gmail.com>
    Reviewed-by: Jiri Pirko <jiri@nvidia.com>
    Link: https://patch.msgid.link/20250303155619.8918-1-oscmaes92@gmail.com
    Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Signed-off-by: Guillaume Nault <gnault@redhat.com>

Approved-by: Hangbin Liu <haliu@redhat.com>
Approved-by: Xin Long <lxin@redhat.com>
Approved-by: CKI KWF Bot <cki-ci-bot+kwf-gitlab-com@redhat.com>

Merged-by: Jan Stancek <jstancek@redhat.com>

Author: jstancek

net/8021q/vlan.c

@@ -131,7 +131,8 @@ int vlan_check_real_dev(struct net_device *real_dev,
 {
 	const char *name = real_dev->name;
 
-	if (real_dev->features & NETIF_F_VLAN_CHALLENGED) {
+	if (real_dev->features & NETIF_F_VLAN_CHALLENGED ||
+	    real_dev->type != ARPHRD_ETHER) {
 		pr_info("VLANs not supported on %s\n", name);
 		NL_SET_ERR_MSG_MOD(extack, "VLANs not supported on device");
 		return -EOPNOTSUPP;