{ "threat_severity" : "Moderate", "public_date" : "2025-07-28T00:00:00Z", "bugzilla" : { "description" : "kernel: net: vlan: fix VLAN 0 refcount imbalance of toggling filtering during runtime", "id" : "2383906", "url" : "https://bugzilla.redhat.com/show_bug.cgi?id=2383906" }, "cvss3" : { "cvss3_base_score" : "5.5", "cvss3_scoring_vector" : "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H", "status" : "verified" }, "cwe" : "CWE-911", "details" : [ "In the Linux kernel, the following vulnerability has been resolved:\nnet: vlan: fix VLAN 0 refcount imbalance of toggling filtering during runtime\nAssuming the \"rx-vlan-filter\" feature is enabled on a net device, the\n8021q module will automatically add or remove VLAN 0 when the net device\nis put administratively up or down, respectively. There are a couple of\nproblems with the above scheme.\nThe first problem is a memory leak that can happen if the \"rx-vlan-filter\"\nfeature is disabled while the device is running:\n# ip link add bond1 up type bond mode 0\n# ethtool -K bond1 rx-vlan-filter off\n# ip link del dev bond1\nWhen the device is put administratively down the \"rx-vlan-filter\"\nfeature is disabled, so the 8021q module will not remove VLAN 0 and the\nmemory will be leaked [1].\nAnother problem that can happen is that the kernel can automatically\ndelete VLAN 0 when the device is put administratively down despite not\nadding it when the device was put administratively up since during that\ntime the \"rx-vlan-filter\" feature was disabled. null-ptr-unref or\nbug_on[2] will be triggered by unregister_vlan_dev() for refcount\nimbalance if toggling filtering during runtime:\n$ ip link add bond0 type bond mode 0\n$ ip link add link bond0 name vlan0 type vlan id 0 protocol 802.1q\n$ ethtool -K bond0 rx-vlan-filter off\n$ ifconfig bond0 up\n$ ethtool -K bond0 rx-vlan-filter on\n$ ifconfig bond0 down\n$ ip link del vlan0\nRoot cause is as below:\nstep1: add vlan0 for real_dev, such as bond, team.\nregister_vlan_dev\nvlan_vid_add(real_dev,htons(ETH_P_8021Q),0) //refcnt=1\nstep2: disable vlan filter feature and enable real_dev\nstep3: change filter from 0 to 1\nvlan_device_event\nvlan_filter_push_vids\nndo_vlan_rx_add_vid //No refcnt added to real_dev vlan0\nstep4: real_dev down\nvlan_device_event\nvlan_vid_del(dev, htons(ETH_P_8021Q), 0); //refcnt=0\nvlan_info_rcu_free //free vlan0\nstep5: delete vlan0\nunregister_vlan_dev\nBUG_ON(!vlan_info); //vlan_info is null\nFix both problems by noting in the VLAN info whether VLAN 0 was\nautomatically added upon NETDEV_UP and based on that decide whether it\nshould be deleted upon NETDEV_DOWN, regardless of the state of the\n\"rx-vlan-filter\" feature.\n[1]\nunreferenced object 0xffff8880068e3100 (size 256):\ncomm \"ip\", pid 384, jiffies 4296130254\nhex dump (first 32 bytes):\n00 20 30 0d 80 88 ff ff 00 00 00 00 00 00 00 00 . 0.............\n00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................\nbacktrace (crc 81ce31fa):\n__kmalloc_cache_noprof+0x2b5/0x340\nvlan_vid_add+0x434/0x940\nvlan_device_event.cold+0x75/0xa8\nnotifier_call_chain+0xca/0x150\n__dev_notify_flags+0xe3/0x250\nrtnl_configure_link+0x193/0x260\nrtnl_newlink_create+0x383/0x8e0\n__rtnl_newlink+0x22c/0xa40\nrtnl_newlink+0x627/0xb00\nrtnetlink_rcv_msg+0x6fb/0xb70\nnetlink_rcv_skb+0x11f/0x350\nnetlink_unicast+0x426/0x710\nnetlink_sendmsg+0x75a/0xc20\n__sock_sendmsg+0xc1/0x150\n____sys_sendmsg+0x5aa/0x7b0\n___sys_sendmsg+0xfc/0x180\n[2]\nkernel BUG at net/8021q/vlan.c:99!\nOops: invalid opcode: 0000 [#1] SMP KASAN PTI\nCPU: 0 UID: 0 PID: 382 Comm: ip Not tainted 6.16.0-rc3 #61 PREEMPT(voluntary)\nHardware name: QEMU Standard PC (i440FX + PIIX, 1996),\nBIOS rel-1.13.0-0-gf21b5a4aeb02-prebuilt.qemu.org 04/01/2014\nRIP: 0010:unregister_vlan_dev (net/8021q/vlan.c:99 (discriminator 1))\nRSP: 0018:ffff88810badf310 EFLAGS: 00010246\nRAX: 0000000000000000 RBX: ffff88810da84000 RCX: ffffffffb47ceb9a\nRDX: dffffc0000000000 RSI: 0000000000000008 RDI: ffff88810e8b43c8\nRBP: 0000000000000000 R08: 0000000000000000 R09: fffffbfff6cefe80\nR10: ffffffffb677f407 R11: ffff88810badf3c0 R12: ffff88810e8b4000\nR13: 0000000000000000 R14: ffff88810642a5c0 R15: 000000000000017e\nFS: 00007f1ff68c20c0(0000) GS:ffff888163a24000(0000) knlGS:0000000000000000\nCS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033\nCR2: 00007f1ff5dad240 CR3: 0000000107e56000 CR4: 00000000000006f0\nCall Trace:\n