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vlan: enforce underlying device type

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[ Upstream commit b33a534610067ade2bdaf2052900aaad99701353 ]

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: 22bedad3ce ("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: Sasha Levin <sashal@kernel.org>
This commit is contained in:
Oscar Maes 2025-03-03 16:56:19 +01:00 committed by Greg Kroah-Hartman
parent 3de809a768
commit 5a515d13e1
1 changed files with 2 additions and 1 deletions
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3
net/8021q/vlan.c
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@ -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;