6.12-stable review patch. If anyone has any objections, please let me know.
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From: Oscar Maes oscmaes92@gmail.com
[ 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: 22bedad3ce11 ("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 --- net/8021q/vlan.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/net/8021q/vlan.c b/net/8021q/vlan.c index e45187b882206..41be38264493d 100644 --- a/net/8021q/vlan.c +++ b/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;