{"id":"CVE-2026-23198","title":"KVM: Don't clobber irqfd routing type when deassigning irqfd","summary":"In the Linux kernel, the following vulnerability has been resolved:\n\nKVM: Don't clobber irqfd routing type when deassigning irqfd\n\nWhen deassigning a KVM_IRQFD, don't clobber the irqfd's copy of the IRQ's\nrouting entry as doing so breaks…","severity":"high","cvss":7.8,"cvssVector":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H","cvssSource":"cna","vendor":"Linux","product":"Linux","affected":["Linux >= f70c20aaf141adb715a2d750c55154073b02a9c3 < 959a063e7f12524bc1871ad1f519787967bbcd45","Linux >= f70c20aaf141adb715a2d750c55154073b02a9c3 < 2284bc168b148a17b5ca3b37b3d95c411f18a08d","Linux >= f70c20aaf141adb715a2d750c55154073b02a9c3 < 6d14ba1e144e796b5fc81044f08cfba9024ca195","Linux >= f70c20aaf141adb715a2d750c55154073b02a9c3 < b61f9b2fcf181451d0a319889478cc53c001123e","Linux >= f70c20aaf141adb715a2d750c55154073b02a9c3 < ff48c9312d042bfbe826ca675e98acc6c623211c","Linux >= f70c20aaf141adb715a2d750c55154073b02a9c3 < 4385b2f2843549bfb932e0dcf76bf4b065543a3c","Linux >= f70c20aaf141adb715a2d750c55154073b02a9c3 < b4d37cdb77a0015f51fee083598fa227cc07aaf1","Linux 4.4"],"ssvc":{"exploitation":"none","automatable":"no","technicalImpact":"total","timestamp":"2026-06-16T20:33:50.365342Z"},"published":"2026-02-14","updated":"2026-10-19","sourceUpdated":"2026-10-19T18:25:35.016Z","source":"CVEORG","sourceUrl":"https://www.cve.org/CVERecord?id=CVE-2026-23198","references":[{"url":"https://git.kernel.org/stable/c/959a063e7f12524bc1871ad1f519787967bbcd45"},{"url":"https://git.kernel.org/stable/c/2284bc168b148a17b5ca3b37b3d95c411f18a08d"},{"url":"https://git.kernel.org/stable/c/6d14ba1e144e796b5fc81044f08cfba9024ca195"},{"url":"https://git.kernel.org/stable/c/b61f9b2fcf181451d0a319889478cc53c001123e"},{"url":"https://git.kernel.org/stable/c/ff48c9312d042bfbe826ca675e98acc6c623211c"},{"url":"https://git.kernel.org/stable/c/4385b2f2843549bfb932e0dcf76bf4b065543a3c"},{"url":"https://git.kernel.org/stable/c/b4d37cdb77a0015f51fee083598fa227cc07aaf1"}],"tags":["cve.org"],"epss":0.00146,"epssPercentile":0.03427,"ingestedAt":"2026-10-19T18:35:50.097Z","slug":"CVE-2026-23198","body":"## Overview\n\nIn the Linux kernel, the following vulnerability has been resolved:\n\nKVM: Don't clobber irqfd routing type when deassigning irqfd\n\nWhen deassigning a KVM_IRQFD, don't clobber the irqfd's copy of the IRQ's\nrouting entry as doing so breaks kvm_arch_irq_bypass_del_producer() on x86\nand arm64, which explicitly look for KVM_IRQ_ROUTING_MSI.  Instead, to\nhandle a concurrent routing update, verify that the irqfd is still active\nbefore consuming the routing information.  As evidenced by the x86 and\narm64 bugs, and another bug in kvm_arch_update_irqfd_routing() (see below),\nclobbering the entry type without notifying arch code is surprising and\nerror prone.\n\nAs a bonus, checking that the irqfd is active provides a convenient\nlocation for documenting _why_ KVM must not consume the routing entry for\nan irqfd that is in the process of being deassigned: once the irqfd is\ndeleted from the list (which happens *before* the eventfd is detached), it\nwill no longer receive updates via kvm_irq_routing_update(), and so KVM\ncould deliver an event using stale routing information (relative to\nKVM_SET_GSI_ROUTING returning to userspace).\n\nAs an even better bonus, explicitly checking for the irqfd being active\nfixes a similar bug to the one the clobbering is trying to prevent: if an\nirqfd is deactivated, and then its routing is changed,\nkvm_irq_routing_update() won't invoke kvm_arch_update_irqfd_routing()\n(because the irqfd isn't in the list).  And so if the irqfd is in bypass\nmode, IRQs will continue to be posted using the old routing information.\n\nAs for kvm_arch_irq_bypass_del_producer(), clobbering the routing type\nresults in KVM incorrectly keeping the IRQ in bypass mode, which is\nespecially problematic on AMD as KVM tracks IRQs that are being posted to\na vCPU in a list whose lifetime is tied to the irqfd.\n\nWithout the help of KASAN to detect use-after-free, the most common\nsympton on AMD is a NULL pointer deref in amd_iommu_update_ga() due to\nthe memory for irqfd structure being re-allocated and zeroed, resulting\nin irqfd->irq_bypass_data being NULL when read by\navic_update_iommu_vcpu_affinity():\n\n  BUG: kernel NULL pointer dereference, address: 0000000000000018\n  #PF: supervisor read access in kernel mode\n  #PF: error_code(0x0000) - not-present page\n  PGD 40cf2b9067 P4D 40cf2b9067 PUD 408362a067 PMD 0\n  Oops: Oops: 0000 [#1] SMP\n  CPU: 6 UID: 0 PID: 40383 Comm: vfio_irq_test\n  Tainted: G     U  W  O        6.19.0-smp--5dddc257e6b2-irqfd #31 NONE\n  Tainted: [U]=USER, [W]=WARN, [O]=OOT_MODULE\n  Hardware name: Google, Inc. Arcadia_IT_80/Arcadia_IT_80, BIOS 34.78.2-0 09/05/2025\n  RIP: 0010:amd_iommu_update_ga+0x19/0xe0\n  Call Trace:\n   <TASK>\n   avic_update_iommu_vcpu_affinity+0x3d/0x90 [kvm_amd]\n   __avic_vcpu_load+0xf4/0x130 [kvm_amd]\n   kvm_arch_vcpu_load+0x89/0x210 [kvm]\n   vcpu_load+0x30/0x40 [kvm]\n   kvm_arch_vcpu_ioctl_run+0x45/0x620 [kvm]\n   kvm_vcpu_ioctl+0x571/0x6a0 [kvm]\n   __se_sys_ioctl+0x6d/0xb0\n   do_syscall_64+0x6f/0x9d0\n   entry_SYSCALL_64_after_hwframe+0x4b/0x53\n  RIP: 0033:0x46893b\n    </TASK>\n  ---[ end trace 0000000000000000 ]---\n\nIf AVIC is inhibited when the irfd is deassigned, the bug will manifest as\nlist corruption, e.g. on the next irqfd assignment.\n\n  list_add corruption. next->prev should be prev (ffff8d474d5cd588),\n                       but was 0000000000000000. (next=ffff8d8658f86530).\n  ------------[ cut here ]------------\n  kernel BUG at lib/list_debug.c:31!\n  Oops: invalid opcode: 0000 [#1] SMP\n  CPU: 128 UID: 0 PID: 80818 Comm: vfio_irq_test\n  Tainted: G     U  W  O        6.19.0-smp--f19dc4d680ba-irqfd #28 NONE\n  Tainted: [U]=USER, [W]=WARN, [O]=OOT_MODULE\n  Hardware name: Google, Inc. Arcadia_IT_80/Arcadia_IT_80, BIOS 34.78.2-0 09/05/2025\n  RIP: 0010:__list_add_valid_or_report+0x97/0xc0\n  Call Trace:\n   <TASK>\n   avic_pi_update_irte+0x28e/0x2b0 [kvm_amd]\n   kvm_pi_update_irte+0xbf/0x190 [kvm]\n   kvm_arch_irq_bypass_add_producer+0x72/0x90 [kvm]\n   irq_bypass_register_consumer+0xcd/0x170 [irqbypa\n---truncated---\n\n## Affected\n\n- `Linux >= f70c20aaf141adb715a2d750c55154073b02a9c3 < 959a063e7f12524bc1871ad1f519787967bbcd45`\n- `Linux >= f70c20aaf141adb715a2d750c55154073b02a9c3 < 2284bc168b148a17b5ca3b37b3d95c411f18a08d`\n- `Linux >= f70c20aaf141adb715a2d750c55154073b02a9c3 < 6d14ba1e144e796b5fc81044f08cfba9024ca195`\n- `Linux >= f70c20aaf141adb715a2d750c55154073b02a9c3 < b61f9b2fcf181451d0a319889478cc53c001123e`\n- `Linux >= f70c20aaf141adb715a2d750c55154073b02a9c3 < ff48c9312d042bfbe826ca675e98acc6c623211c`\n- `Linux >= f70c20aaf141adb715a2d750c55154073b02a9c3 < 4385b2f2843549bfb932e0dcf76bf4b065543a3c`\n- `Linux >= f70c20aaf141adb715a2d750c55154073b02a9c3 < b4d37cdb77a0015f51fee083598fa227cc07aaf1`\n- `Linux 4.4`\n\n## Remediation\n\nRefer to the linked advisories for vendor-supplied fixes and affected version ranges.","depth":"twilight","depthScore":43,"depthScoreParts":{"impact":42.9,"likelihood":0,"exploitation":0,"ransomware":0},"changes":[]}