CVE-2025-38470

In the Linux kernel, the following vulnerability has been resolved:<br /> <br /> net: vlan: fix VLAN 0 refcount imbalance of toggling filtering during runtime<br /> <br /> Assuming the "rx-vlan-filter" feature is enabled on a net device, the<br /> 8021q module will automatically add or remove VLAN 0 when the net device<br /> is put administratively up or down, respectively. There are a couple of<br /> problems with the above scheme.<br /> <br /> The first problem is a memory leak that can happen if the "rx-vlan-filter"<br /> feature is disabled while the device is running:<br /> <br /> # ip link add bond1 up type bond mode 0<br /> # ethtool -K bond1 rx-vlan-filter off<br /> # ip link del dev bond1<br /> <br /> When the device is put administratively down the "rx-vlan-filter"<br /> feature is disabled, so the 8021q module will not remove VLAN 0 and the<br /> memory will be leaked [1].<br /> <br /> Another problem that can happen is that the kernel can automatically<br /> delete VLAN 0 when the device is put administratively down despite not<br /> adding it when the device was put administratively up since during that<br /> time the "rx-vlan-filter" feature was disabled. null-ptr-unref or<br /> bug_on[2] will be triggered by unregister_vlan_dev() for refcount<br /> imbalance if toggling filtering during runtime:<br /> <br /> $ ip link add bond0 type bond mode 0<br /> $ ip link add link bond0 name vlan0 type vlan id 0 protocol 802.1q<br /> $ ethtool -K bond0 rx-vlan-filter off<br /> $ ifconfig bond0 up<br /> $ ethtool -K bond0 rx-vlan-filter on<br /> $ ifconfig bond0 down<br /> $ ip link del vlan0<br /> <br /> Root cause is as below:<br /> step1: add vlan0 for real_dev, such as bond, team.<br /> register_vlan_dev<br /> vlan_vid_add(real_dev,htons(ETH_P_8021Q),0) //refcnt=1<br /> step2: disable vlan filter feature and enable real_dev<br /> step3: change filter from 0 to 1<br /> vlan_device_event<br /> vlan_filter_push_vids<br /> ndo_vlan_rx_add_vid //No refcnt added to real_dev vlan0<br /> step4: real_dev down<br /> vlan_device_event<br /> vlan_vid_del(dev, htons(ETH_P_8021Q), 0); //refcnt=0<br /> vlan_info_rcu_free //free vlan0<br /> step5: delete vlan0<br /> unregister_vlan_dev<br /> BUG_ON(!vlan_info); //vlan_info is null<br /> <br /> Fix both problems by noting in the VLAN info whether VLAN 0 was<br /> automatically added upon NETDEV_UP and based on that decide whether it<br /> should be deleted upon NETDEV_DOWN, regardless of the state of the<br /> "rx-vlan-filter" feature.<br /> <br /> [1]<br /> unreferenced object 0xffff8880068e3100 (size 256):<br /> comm "ip", pid 384, jiffies 4296130254<br /> hex dump (first 32 bytes):<br /> 00 20 30 0d 80 88 ff ff 00 00 00 00 00 00 00 00 . 0.............<br /> 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................<br /> backtrace (crc 81ce31fa):<br /> __kmalloc_cache_noprof+0x2b5/0x340<br /> vlan_vid_add+0x434/0x940<br /> vlan_device_event.cold+0x75/0xa8<br /> notifier_call_chain+0xca/0x150<br /> __dev_notify_flags+0xe3/0x250<br /> rtnl_configure_link+0x193/0x260<br /> rtnl_newlink_create+0x383/0x8e0<br /> __rtnl_newlink+0x22c/0xa40<br /> rtnl_newlink+0x627/0xb00<br /> rtnetlink_rcv_msg+0x6fb/0xb70<br /> netlink_rcv_skb+0x11f/0x350<br /> netlink_unicast+0x426/0x710<br /> netlink_sendmsg+0x75a/0xc20<br /> __sock_sendmsg+0xc1/0x150<br /> ____sys_sendmsg+0x5aa/0x7b0<br /> ___sys_sendmsg+0xfc/0x180<br /> <br /> [2]<br /> kernel BUG at net/8021q/vlan.c:99!<br /> Oops: invalid opcode: 0000 [#1] SMP KASAN PTI<br /> CPU: 0 UID: 0 PID: 382 Comm: ip Not tainted 6.16.0-rc3 #61 PREEMPT(voluntary)<br /> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996),<br /> BIOS rel-1.13.0-0-gf21b5a4aeb02-prebuilt.qemu.org 04/01/2014<br /> RIP: 0010:unregister_vlan_dev (net/8021q/vlan.c:99 (discriminator 1))<br /> RSP: 0018:ffff88810badf310 EFLAGS: 00010246<br /> RAX: 0000000000000000 RBX: ffff88810da84000 RCX: ffffffffb47ceb9a<br /> RDX: dffffc0000000000 RSI: 0000000000000008 RDI: ffff88810e8b43c8<br /> RBP: 0000000000000000 R08: 0000000000000000 R09: fffffbfff6cefe80<br /> R10: ffffffffb677f407 R11: ffff88810badf3c0 R12: ffff88810e8b4000<br /> R13: 0000000000000000 R14: ffff88810642a5c0 R15: 000000000000017e<br /> FS: 00007f1ff68c20c0(0000) GS:ffff888163a24000(0000) knlGS:0000000000000000<br /> CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033<br /> CR2: 00007f1ff5dad240 CR3: 0000000107e56000 CR4: 00000000000006f0<br /> Call Trace:<br />