In the Linux kernel, the following vulnerability has been resolved:
bpf: reject unhashed sockets in bpf_sk_assign
The semantics for bpf_sk_assign are as follows:
sk = some_lookup_func() bpf_sk_assign(skb, sk) bpf_sk_release(sk)
That is, the sk is not consumed by bpf_sk_assign. The function therefore needs to make sure that sk lives long enough to be consumed from __inet_lookup_skb. The path through the stack for a TCPv4 packet is roughly:
netif_receive_skb_core: takes RCU read lock __netif_receive_skb_core: sch_handle_ingress: tcf_classify: bpf_sk_assign() deliver_ptype_list_skb: deliver_skb: ip_packet_type->func == ip_rcv: ip_rcv_core: ip_rcv_finish_core: dst_input: ip_local_deliver: ip_local_deliver_finish: ip_protocol_deliver_rcu: tcp_v4_rcv: __inet_lookup_skb: skb_steal_sock
The existing helper takes advantage of the fact that everything happens in the same RCU critical section: for sockets with SOCK_RCU_FREE set bpf_sk_assign never takes a reference. skb_steal_sock then checks SOCK_RCU_FREE again and does sock_put if necessary.
This approach assumes that SOCK_RCU_FREE is never set on a sk between bpf_sk_assign and skb_steal_sock, but this invariant is violated by unhashed UDP sockets. A new UDP socket is created in TCP_CLOSE state but without SOCK_RCU_FREE set. That flag is only added in udp_lib_get_port() which happens when a socket is bound.
When bpf_sk_assign was added it wasn't possible to access unhashed UDP sockets from BPF, so this wasn't a problem. This changed in commit 0c48eefae712 ("sock_map: Lift socket state restriction for datagram sockets"), but the helper wasn't adjusted accordingly. The following sequence of events will therefore lead to a refcount leak:
1. Add socket(AF_INET, SOCK_DGRAM) to a sockmap. 2. Pull socket out of sockmap and bpf_sk_assign it. Since SOCK_RCU_FREE is not set we increment the refcount. 3. bind() or connect() the socket, setting SOCK_RCU_FREE. 4. skb_steal_sock will now set refcounted = false due to SOCK_RCU_FREE. 5. tcp_v4_rcv() skips sock_put().
Fix the problem by rejecting unhashed sockets in bpf_sk_assign(). This matches the behaviour of __inet_lookup_skb which is ultimately the goal of bpf_sk_assign().
CVSS Details
- CVSS 3.1 Base Score: 5.5
- CVSS 3.1 Vector: (CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H)
Covered by Rapid7
| Product | Vendor Advisory | Solution File | Added | Published |
|---|---|---|---|---|
| Amazon Linux Ami 2 | — | Upgrade kernel-develUpgrade kernel-toolsUpgrade python-perfUpgrade kernel-livepatch-5.10.196-185.743Upgrade bpftoolUpgrade kernel-debuginfo-common-aarch64Upgrade perfUpgrade kernel-livepatch-5.15.133-86.144Upgrade kernel-debuginfo-common-x86_64Upgrade bpftool-debuginfoUpgrade kernel-debuginfoUpgrade perf-debuginfoUpgrade kernelUpgrade kernel-headersUpgrade kernel-tools-debuginfoUpgrade python-perf-debuginfoUpgrade kernel-tools-devel | May 20, 2026 | May 20, 2026 |
| Amazon_linux_2023 | — | Upgrade python3-perfUpgrade kernel-debuginfo-common-aarch64Upgrade bpftoolUpgrade perf-debuginfoUpgrade kernel-tools-develUpgrade kernel-debuginfoUpgrade kernel-livepatch-6.1.55-75.123Upgrade kernel-libbpfUpgrade perfUpgrade python3-perf-debuginfoUpgrade kernel-tools-debuginfoUpgrade kernel-develUpgrade kernel-debuginfo-common-x86_64Upgrade kernel-libbpf-staticUpgrade kernelUpgrade kernel-headersUpgrade kernel-toolsUpgrade bpftool-debuginfoUpgrade kernel-libbpf-devel | Oct 24, 2025 | Oct 4, 2025 |
| Debian | — | Upgrade linux | Oct 6, 2025 | Oct 6, 2025 |
| Huawei Euleros 2_0_sp13 | — | Upgrade python3-perfUpgrade bpftoolUpgrade kernelUpgrade kernel-toolsUpgrade kernel-tools-libsUpgrade kernel-abi-stablelists | Feb 3, 2026 | Feb 2, 2026 |
| Redhat_linux | — | Upgrade kernel-rtNo solution existsUpgrade kernel | Nov 14, 2025 | Oct 4, 2025 |
| Ubuntu | — | Upgrade linux-gcpUpgrade linux-gcp-5.15Upgrade linux-lowlatency-hwe-5.15Upgrade linux-bluefieldUpgrade linux-intel-iot-realtimeUpgrade linux-realtimeUpgrade linux-nvidia-tegra-igxUpgrade linux-gcp-fipsUpgrade linux-nvidia-tegra-5.15Upgrade linux-awsUpgrade linux-fipsUpgrade linux-azure-5.15Upgrade linux-azureUpgrade linux-xilinx-zynqmpUpgrade linux-aws-fipsUpgrade linux-hwe-5.15Upgrade linux-lowlatencyUpgrade linux-aws-5.15Upgrade linux-gkeopUpgrade linux-raspiUpgrade linux-intel-iotgUpgrade linux-nvidia-tegraUpgrade linux-riscv-5.15Upgrade linux-oracle-5.15Upgrade linuxUpgrade linux-ibmUpgrade linux-ibm-5.15Upgrade linux-oracleUpgrade linux-intel-iotg-5.15Upgrade linux-kvmUpgrade linux-gkeUpgrade linux-nvidia | Oct 10, 2025 | Oct 4, 2025 |
| Vmware Photon_os | — | Use 'tdnf update' to upgrade all packages to the latest version. | Oct 15, 2025 | Oct 4, 2025 |
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