CVE Vulnerabilities

CVE-2025-38472

Published: Jul 28, 2025 | Modified: Jul 29, 2025
CVSS 3.x
N/A
Source:
NVD
CVSS 2.x
RedHat/V2
RedHat/V3
7.1 MODERATE
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:H
Ubuntu
MEDIUM

In the Linux kernel, the following vulnerability has been resolved:

netfilter: nf_conntrack: fix crash due to removal of uninitialised entry

A crash in conntrack was reported while trying to unlink the conntrack entry from the hash bucket list: [exception RIP: __nf_ct_delete_from_lists+172] [..] #7 [ff539b5a2b043aa0] nf_ct_delete at ffffffffc124d421 [nf_conntrack] #8 [ff539b5a2b043ad0] nf_ct_gc_expired at ffffffffc124d999 [nf_conntrack] #9 [ff539b5a2b043ae0] __nf_conntrack_find_get at ffffffffc124efbc [nf_conntrack] [..]

The nf_conn struct is marked as allocated from slab but appears to be in a partially initialised state:

ct hlist pointer is garbage; looks like the ct hash value (hence crash). ct->status is equal to IPS_CONFIRMED|IPS_DYING, which is expected ct->timeout is 30000 (=30s), which is unexpected.

Everything else looks like normal udp conntrack entry. If we ignore ct->status and pretend its 0, the entry matches those that are newly allocated but not yet inserted into the hash:

  • ct hlist pointers are overloaded and store/cache the raw tuple hash
  • ct->timeout matches the relative time expected for a new udp flow rather than the absolute jiffies value.

If it were not for the presence of IPS_CONFIRMED, __nf_conntrack_find_get() would have skipped the entry.

Theory is that we did hit following race:

cpu x cpu y cpu z found entry E found entry E E is expired nf_ct_delete() return E to rcu slab init_conntrack E is re-inited, ct->status set to 0 reply tuplehash hnnode.pprev stores hash value.

cpu y found E right before it was deleted on cpu x. E is now re-inited on cpu z. cpu y was preempted before checking for expiry and/or confirm bit.

				->refcnt set to 1
				E now owned by skb
				->timeout set to 30000

If cpu y were to resume now, it would observe E as expired but would skip E due to missing CONFIRMED bit.

				nf_conntrack_confirm gets called
				sets: ct->status |= CONFIRMED
				This is wrong: E is not yet added
				to hashtable.

cpu y resumes, it observes E as expired but CONFIRMED: nf_ct_expired() -> yes (ct->timeout is 30s) confirmed bit set.

cpu y will try to delete E from the hashtable: nf_ct_delete() -> set DYING bit __nf_ct_delete_from_lists

Even this scenario doesnt guarantee a crash: cpu z still holds the table bucket lock(s) so y blocks:

		wait for spinlock held by z

				CONFIRMED is set but there is no
				guarantee ct will be added to hash:
				chaintoolong or clash resolution
				logic both skip the insert step.
				reply hnnode.pprev still stores the
				hash value.

				unlocks spinlock
				return NF_DROP
		<unblocks, then
		 crashes on hlist_nulls_del_rcu pprev>

In case CPU z does insert the entry into the hashtable, cpu y will unlink E again right away but no crash occurs.

Without cpu y race, garbage hlist is of no consequence: ct refcnt remains at 1, eventually skb will be freed and E gets destroyed via: nf_conntrack_put -> nf_conntrack_destroy -> nf_ct_destroy.

To resolve this, move the IPS_CONFIRMED assignment after the table insertion but before the unlock.

Pablo points out that the confirm-bit-store could be reordered to happen before hlist add resp. the timeout fixup, so switch to set_bit and before_atomic memory barrier to prevent this.

It doesnt matter if other CPUs can observe a newly inserted entry right before the CONFIRMED bit was set:

Such event cannot be distinguished from above E is the old incarnation case: the entry will be skipped.

Also change nf_ct_should_gc() to first check the confirmed bit.

The gc sequence is:

  1. Check if entry has expired, if not skip to next entry
  2. Obtain a reference to the expired entry.
  3. Call nf_ct_should_gc() to double-check step 1.

nf_ct_should_gc() is thus called only for entries that already failed an expiry check. After this patch, once the confirmed bit check pas —truncated—

Affected Software

Name Vendor Start Version End Version
Linux Ubuntu devel *
Linux Ubuntu noble *
Linux Ubuntu plucky *
Linux Ubuntu upstream *
Linux-allwinner-5.19 Ubuntu jammy *
Linux-allwinner-5.19 Ubuntu upstream *
Linux-aws Ubuntu devel *
Linux-aws Ubuntu noble *
Linux-aws Ubuntu plucky *
Linux-aws Ubuntu upstream *
Linux-aws-5.0 Ubuntu bionic *
Linux-aws-5.0 Ubuntu esm-infra/bionic *
Linux-aws-5.0 Ubuntu upstream *
Linux-aws-5.11 Ubuntu esm-infra/focal *
Linux-aws-5.11 Ubuntu focal *
Linux-aws-5.11 Ubuntu upstream *
Linux-aws-5.13 Ubuntu esm-infra/focal *
Linux-aws-5.13 Ubuntu focal *
Linux-aws-5.13 Ubuntu upstream *
Linux-aws-5.15 Ubuntu upstream *
Linux-aws-5.19 Ubuntu jammy *
Linux-aws-5.19 Ubuntu upstream *
Linux-aws-5.3 Ubuntu bionic *
Linux-aws-5.3 Ubuntu esm-infra/bionic *
Linux-aws-5.3 Ubuntu upstream *
Linux-aws-5.4 Ubuntu upstream *
Linux-aws-5.8 Ubuntu esm-infra/focal *
Linux-aws-5.8 Ubuntu focal *
Linux-aws-5.8 Ubuntu upstream *
Linux-aws-6.14 Ubuntu noble *
Linux-aws-6.14 Ubuntu upstream *
Linux-aws-6.2 Ubuntu jammy *
Linux-aws-6.2 Ubuntu upstream *
Linux-aws-6.5 Ubuntu jammy *
Linux-aws-6.5 Ubuntu upstream *
Linux-aws-6.8 Ubuntu jammy *
Linux-aws-6.8 Ubuntu upstream *
Linux-aws-fips Ubuntu trusty *
Linux-aws-fips Ubuntu upstream *
Linux-aws-fips Ubuntu xenial *
Linux-aws-hwe Ubuntu upstream *
Linux-azure Ubuntu bionic *
Linux-azure Ubuntu devel *
Linux-azure Ubuntu esm-infra/bionic *
Linux-azure Ubuntu noble *
Linux-azure Ubuntu plucky *
Linux-azure Ubuntu upstream *
Linux-azure-4.15 Ubuntu upstream *
Linux-azure-5.11 Ubuntu esm-infra/focal *
Linux-azure-5.11 Ubuntu focal *
Linux-azure-5.11 Ubuntu upstream *
Linux-azure-5.13 Ubuntu esm-infra/focal *
Linux-azure-5.13 Ubuntu focal *
Linux-azure-5.13 Ubuntu upstream *
Linux-azure-5.15 Ubuntu upstream *
Linux-azure-5.19 Ubuntu jammy *
Linux-azure-5.19 Ubuntu upstream *
Linux-azure-5.3 Ubuntu bionic *
Linux-azure-5.3 Ubuntu esm-infra/bionic *
Linux-azure-5.3 Ubuntu upstream *
Linux-azure-5.4 Ubuntu upstream *
Linux-azure-5.8 Ubuntu esm-infra/focal *
Linux-azure-5.8 Ubuntu focal *
Linux-azure-5.8 Ubuntu upstream *
Linux-azure-6.11 Ubuntu noble *
Linux-azure-6.11 Ubuntu upstream *
Linux-azure-6.2 Ubuntu jammy *
Linux-azure-6.2 Ubuntu upstream *
Linux-azure-6.5 Ubuntu jammy *
Linux-azure-6.5 Ubuntu upstream *
Linux-azure-6.8 Ubuntu jammy *
Linux-azure-6.8 Ubuntu upstream *
Linux-azure-edge Ubuntu bionic *
Linux-azure-edge Ubuntu esm-infra/bionic *
Linux-azure-edge Ubuntu upstream *
Linux-azure-fde Ubuntu esm-infra/focal *
Linux-azure-fde Ubuntu focal *
Linux-azure-fde Ubuntu upstream *
Linux-azure-fde-5.15 Ubuntu upstream *
Linux-azure-fde-5.19 Ubuntu jammy *
Linux-azure-fde-5.19 Ubuntu upstream *
Linux-azure-fde-6.2 Ubuntu jammy *
Linux-azure-fde-6.2 Ubuntu upstream *
Linux-azure-fips Ubuntu trusty *
Linux-azure-fips Ubuntu upstream *
Linux-azure-fips Ubuntu xenial *
Linux-azure-nvidia Ubuntu noble *
Linux-azure-nvidia Ubuntu upstream *
Linux-bluefield Ubuntu upstream *
Linux-fips Ubuntu upstream *
Linux-gcp Ubuntu bionic *
Linux-gcp Ubuntu devel *
Linux-gcp Ubuntu esm-infra/bionic *
Linux-gcp Ubuntu noble *
Linux-gcp Ubuntu plucky *
Linux-gcp Ubuntu upstream *
Linux-gcp-4.15 Ubuntu upstream *
Linux-gcp-5.11 Ubuntu esm-infra/focal *
Linux-gcp-5.11 Ubuntu focal *
Linux-gcp-5.11 Ubuntu upstream *
Linux-gcp-5.13 Ubuntu esm-infra/focal *
Linux-gcp-5.13 Ubuntu focal *
Linux-gcp-5.13 Ubuntu upstream *
Linux-gcp-5.15 Ubuntu upstream *
Linux-gcp-5.19 Ubuntu jammy *
Linux-gcp-5.19 Ubuntu upstream *
Linux-gcp-5.3 Ubuntu bionic *
Linux-gcp-5.3 Ubuntu esm-infra/bionic *
Linux-gcp-5.3 Ubuntu upstream *
Linux-gcp-5.4 Ubuntu upstream *
Linux-gcp-5.8 Ubuntu esm-infra/focal *
Linux-gcp-5.8 Ubuntu focal *
Linux-gcp-5.8 Ubuntu upstream *
Linux-gcp-6.11 Ubuntu noble *
Linux-gcp-6.11 Ubuntu upstream *
Linux-gcp-6.14 Ubuntu noble *
Linux-gcp-6.14 Ubuntu upstream *
Linux-gcp-6.2 Ubuntu jammy *
Linux-gcp-6.2 Ubuntu upstream *
Linux-gcp-6.5 Ubuntu jammy *
Linux-gcp-6.5 Ubuntu upstream *
Linux-gcp-6.8 Ubuntu jammy *
Linux-gcp-6.8 Ubuntu upstream *
Linux-gcp-fips Ubuntu trusty *
Linux-gcp-fips Ubuntu upstream *
Linux-gcp-fips Ubuntu xenial *
Linux-gke Ubuntu esm-infra/focal *
Linux-gke Ubuntu focal *
Linux-gke Ubuntu noble *
Linux-gke Ubuntu upstream *
Linux-gke Ubuntu xenial *
Linux-gke-4.15 Ubuntu bionic *
Linux-gke-4.15 Ubuntu esm-infra/bionic *
Linux-gke-4.15 Ubuntu upstream *
Linux-gke-5.15 Ubuntu esm-infra/focal *
Linux-gke-5.15 Ubuntu focal *
Linux-gke-5.15 Ubuntu upstream *
Linux-gke-5.4 Ubuntu bionic *
Linux-gke-5.4 Ubuntu esm-infra/bionic *
Linux-gke-5.4 Ubuntu upstream *
Linux-gkeop Ubuntu esm-infra/focal *
Linux-gkeop Ubuntu focal *
Linux-gkeop Ubuntu noble *
Linux-gkeop Ubuntu upstream *
Linux-gkeop-5.15 Ubuntu esm-infra/focal *
Linux-gkeop-5.15 Ubuntu focal *
Linux-gkeop-5.15 Ubuntu upstream *
Linux-gkeop-5.4 Ubuntu bionic *
Linux-gkeop-5.4 Ubuntu esm-infra/bionic *
Linux-gkeop-5.4 Ubuntu upstream *
Linux-hwe Ubuntu bionic *
Linux-hwe Ubuntu esm-infra/bionic *
Linux-hwe Ubuntu upstream *
Linux-hwe-5.11 Ubuntu esm-infra/focal *
Linux-hwe-5.11 Ubuntu focal *
Linux-hwe-5.11 Ubuntu upstream *
Linux-hwe-5.13 Ubuntu esm-infra/focal *
Linux-hwe-5.13 Ubuntu focal *
Linux-hwe-5.13 Ubuntu upstream *
Linux-hwe-5.15 Ubuntu upstream *
Linux-hwe-5.19 Ubuntu jammy *
Linux-hwe-5.19 Ubuntu upstream *
Linux-hwe-5.4 Ubuntu upstream *
Linux-hwe-5.8 Ubuntu esm-infra/focal *
Linux-hwe-5.8 Ubuntu focal *
Linux-hwe-5.8 Ubuntu upstream *
Linux-hwe-6.11 Ubuntu noble *
Linux-hwe-6.11 Ubuntu upstream *
Linux-hwe-6.14 Ubuntu noble *
Linux-hwe-6.14 Ubuntu upstream *
Linux-hwe-6.2 Ubuntu jammy *
Linux-hwe-6.2 Ubuntu upstream *
Linux-hwe-6.5 Ubuntu jammy *
Linux-hwe-6.5 Ubuntu upstream *
Linux-hwe-6.8 Ubuntu jammy *
Linux-hwe-6.8 Ubuntu upstream *
Linux-hwe-edge Ubuntu bionic *
Linux-hwe-edge Ubuntu esm-infra/bionic *
Linux-hwe-edge Ubuntu esm-infra/xenial *
Linux-hwe-edge Ubuntu upstream *
Linux-hwe-edge Ubuntu xenial *
Linux-ibm Ubuntu noble *
Linux-ibm Ubuntu upstream *
Linux-ibm-5.15 Ubuntu upstream *
Linux-ibm-5.4 Ubuntu upstream *
Linux-ibm-6.8 Ubuntu jammy *
Linux-ibm-6.8 Ubuntu upstream *
Linux-intel Ubuntu noble *
Linux-intel Ubuntu upstream *
Linux-intel-5.13 Ubuntu esm-infra/focal *
Linux-intel-5.13 Ubuntu focal *
Linux-intel-5.13 Ubuntu upstream *
Linux-intel-iot-realtime Ubuntu jammy *
Linux-intel-iot-realtime Ubuntu upstream *
Linux-intel-iotg Ubuntu upstream *
Linux-intel-iotg-5.15 Ubuntu upstream *
Linux-iot Ubuntu upstream *
Linux-kvm Ubuntu upstream *
Linux-lowlatency Ubuntu noble *
Linux-lowlatency Ubuntu upstream *
Linux-lowlatency-hwe-5.15 Ubuntu upstream *
Linux-lowlatency-hwe-5.19 Ubuntu jammy *
Linux-lowlatency-hwe-5.19 Ubuntu upstream *
Linux-lowlatency-hwe-6.11 Ubuntu noble *
Linux-lowlatency-hwe-6.11 Ubuntu upstream *
Linux-lowlatency-hwe-6.2 Ubuntu jammy *
Linux-lowlatency-hwe-6.2 Ubuntu upstream *
Linux-lowlatency-hwe-6.5 Ubuntu jammy *
Linux-lowlatency-hwe-6.5 Ubuntu upstream *
Linux-lowlatency-hwe-6.8 Ubuntu jammy *
Linux-lowlatency-hwe-6.8 Ubuntu upstream *
Linux-lts-xenial Ubuntu upstream *
Linux-nvidia Ubuntu noble *
Linux-nvidia Ubuntu upstream *
Linux-nvidia-6.11 Ubuntu noble *
Linux-nvidia-6.11 Ubuntu upstream *
Linux-nvidia-6.2 Ubuntu jammy *
Linux-nvidia-6.2 Ubuntu upstream *
Linux-nvidia-6.5 Ubuntu jammy *
Linux-nvidia-6.5 Ubuntu upstream *
Linux-nvidia-6.8 Ubuntu jammy *
Linux-nvidia-6.8 Ubuntu upstream *
Linux-nvidia-lowlatency Ubuntu noble *
Linux-nvidia-lowlatency Ubuntu upstream *
Linux-nvidia-tegra Ubuntu noble *
Linux-nvidia-tegra Ubuntu upstream *
Linux-nvidia-tegra-5.15 Ubuntu upstream *
Linux-nvidia-tegra-igx Ubuntu upstream *
Linux-oem Ubuntu bionic *
Linux-oem Ubuntu esm-infra/bionic *
Linux-oem Ubuntu upstream *
Linux-oem Ubuntu xenial *
Linux-oem-5.10 Ubuntu esm-infra/focal *
Linux-oem-5.10 Ubuntu focal *
Linux-oem-5.10 Ubuntu upstream *
Linux-oem-5.13 Ubuntu esm-infra/focal *
Linux-oem-5.13 Ubuntu focal *
Linux-oem-5.13 Ubuntu upstream *
Linux-oem-5.14 Ubuntu esm-infra/focal *
Linux-oem-5.14 Ubuntu focal *
Linux-oem-5.14 Ubuntu upstream *
Linux-oem-5.17 Ubuntu jammy *
Linux-oem-5.17 Ubuntu upstream *
Linux-oem-5.6 Ubuntu esm-infra/focal *
Linux-oem-5.6 Ubuntu focal *
Linux-oem-5.6 Ubuntu upstream *
Linux-oem-6.0 Ubuntu jammy *
Linux-oem-6.0 Ubuntu upstream *
Linux-oem-6.1 Ubuntu jammy *
Linux-oem-6.1 Ubuntu upstream *
Linux-oem-6.11 Ubuntu noble *
Linux-oem-6.11 Ubuntu upstream *
Linux-oem-6.14 Ubuntu noble *
Linux-oem-6.14 Ubuntu upstream *
Linux-oem-6.5 Ubuntu jammy *
Linux-oem-6.5 Ubuntu upstream *
Linux-oem-6.8 Ubuntu noble *
Linux-oem-6.8 Ubuntu upstream *
Linux-oracle Ubuntu devel *
Linux-oracle Ubuntu noble *
Linux-oracle Ubuntu plucky *
Linux-oracle Ubuntu upstream *
Linux-oracle-5.0 Ubuntu bionic *
Linux-oracle-5.0 Ubuntu esm-infra/bionic *
Linux-oracle-5.0 Ubuntu upstream *
Linux-oracle-5.11 Ubuntu esm-infra/focal *
Linux-oracle-5.11 Ubuntu focal *
Linux-oracle-5.11 Ubuntu upstream *
Linux-oracle-5.13 Ubuntu esm-infra/focal *
Linux-oracle-5.13 Ubuntu focal *
Linux-oracle-5.13 Ubuntu upstream *
Linux-oracle-5.15 Ubuntu upstream *
Linux-oracle-5.3 Ubuntu bionic *
Linux-oracle-5.3 Ubuntu esm-infra/bionic *
Linux-oracle-5.3 Ubuntu upstream *
Linux-oracle-5.4 Ubuntu upstream *
Linux-oracle-5.8 Ubuntu esm-infra/focal *
Linux-oracle-5.8 Ubuntu focal *
Linux-oracle-5.8 Ubuntu upstream *
Linux-oracle-6.14 Ubuntu noble *
Linux-oracle-6.14 Ubuntu upstream *
Linux-oracle-6.5 Ubuntu jammy *
Linux-oracle-6.5 Ubuntu upstream *
Linux-oracle-6.8 Ubuntu jammy *
Linux-oracle-6.8 Ubuntu upstream *
Linux-raspi Ubuntu devel *
Linux-raspi Ubuntu noble *
Linux-raspi Ubuntu plucky *
Linux-raspi Ubuntu upstream *
Linux-raspi-5.4 Ubuntu upstream *
Linux-raspi-realtime Ubuntu noble *
Linux-raspi-realtime Ubuntu realtime/noble *
Linux-raspi-realtime Ubuntu upstream *
Linux-raspi2 Ubuntu bionic *
Linux-raspi2 Ubuntu esm-infra/focal *
Linux-raspi2 Ubuntu focal *
Linux-raspi2 Ubuntu upstream *
Linux-raspi2 Ubuntu xenial *
Linux-realtime Ubuntu devel *
Linux-realtime Ubuntu jammy *
Linux-realtime Ubuntu noble *
Linux-realtime Ubuntu plucky *
Linux-realtime Ubuntu realtime/noble *
Linux-realtime Ubuntu upstream *
Linux-riscv Ubuntu devel *
Linux-riscv Ubuntu esm-infra/focal *
Linux-riscv Ubuntu focal *
Linux-riscv Ubuntu jammy *
Linux-riscv Ubuntu noble *
Linux-riscv Ubuntu plucky *
Linux-riscv Ubuntu upstream *
Linux-riscv-5.11 Ubuntu esm-infra/focal *
Linux-riscv-5.11 Ubuntu focal *
Linux-riscv-5.11 Ubuntu upstream *
Linux-riscv-5.15 Ubuntu upstream *
Linux-riscv-5.19 Ubuntu jammy *
Linux-riscv-5.19 Ubuntu upstream *
Linux-riscv-5.8 Ubuntu esm-infra/focal *
Linux-riscv-5.8 Ubuntu focal *
Linux-riscv-5.8 Ubuntu upstream *
Linux-riscv-6.14 Ubuntu noble *
Linux-riscv-6.14 Ubuntu upstream *
Linux-riscv-6.5 Ubuntu jammy *
Linux-riscv-6.5 Ubuntu upstream *
Linux-riscv-6.8 Ubuntu jammy *
Linux-riscv-6.8 Ubuntu upstream *
Linux-starfive-5.19 Ubuntu jammy *
Linux-starfive-5.19 Ubuntu upstream *
Linux-starfive-6.2 Ubuntu jammy *
Linux-starfive-6.2 Ubuntu upstream *
Linux-starfive-6.5 Ubuntu jammy *
Linux-starfive-6.5 Ubuntu upstream *
Linux-xilinx-zynqmp Ubuntu upstream *

References