CVE-2026-89902 (GCVE-0-2026-89902)

Vulnerability from cvelistv5 – Published: 2026-09-16 10:32 – Updated: 2026-09-16 14:39
VLAI
Title
LoongArch: Avoid preempt count underflow without probe
Summary
In the Linux kernel, the following vulnerability has been resolved: LoongArch: Avoid preempt count underflow without probe LoongArch uses break 11 for the breakpoint placed after an instruction that Kprobes executes out of line. Since userspace can issue the same break instruction, do_bp() can reach kprobe_singlestep_handler() when there is no current probe. The handler actually returns false in this case, but it first calls preempt_enable_no_resched(). The corresponding preempt_disable() is done by kprobe_breakpoint_handler() on a real Kprobe hit, so it has not run here. As a result, an ordinary userspace breakpoint (code 11) underflows the current task's preempt count. This also makes in_interrupt() return true until the task schedules. One visible consequence is the socket cgroup attribution: cgroup_sk_alloc() treats the allocation as interrupt context and assigns the socket to the root cgroup. A socket opened from the SIGTRAP handler can then avoid a BPF_CGROUP_INET_SOCK_CREATE policy attached to the task's own cgroup. Return as soon as kprobe_running() reports no active probe. The same check has appeared in [PATCH v10 2/4] of the original LoongArch Kprobes series, but was dropped before the feature reached mainline.
Severity
7.8 (High)
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
Assigner
References
Impacted products
Vendor Product Version CPE status
Linux Linux Affected: 6d4cc40fb5f58147defc6c0e9d86e6232fe31616 , < ff40e597d5d98c0c45a4d09df8177202fac9520e (git)
Affected: 6d4cc40fb5f58147defc6c0e9d86e6232fe31616 , < a1cb727fa27c2d9c7859729cd90db7bc0f46957f (git)
Affected: 6d4cc40fb5f58147defc6c0e9d86e6232fe31616 , < 76395109a051b53860faaec96522ef08ae9e8e27 (git)
Affected: 6d4cc40fb5f58147defc6c0e9d86e6232fe31616 , < c4357ebeee63cb8da1446fc936573a34e68b0f71 (git)
Affected: 6d4cc40fb5f58147defc6c0e9d86e6232fe31616 , < 72ce4b24676e8b3b75376c4c559dd81c1ac52d5a (git)
guessed Create a notification for this product.
Linux Linux Affected: 6.3
Unaffected: 0 , < 6.3 (semver)
Unaffected: 6.6.157 , ≤ 6.6.* (semver)
Unaffected: 6.12.110 , ≤ 6.12.* (semver)
Unaffected: 6.18.51 , ≤ 6.18.* (semver)
Unaffected: 7.2.5 , ≤ 7.2.* (semver)
Unaffected: 7.3-rc2 , ≤ * (original_commit_for_fix)
guessed Create a notification for this product.
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{
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      "affected": [
        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
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          "vendor": "Linux",
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              "versionType": "semver"
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              "status": "unaffected",
              "version": "6.18.51",
              "versionType": "semver"
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              "status": "unaffected",
              "version": "7.2.5",
              "versionType": "semver"
            },
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              "status": "unaffected",
              "version": "7.3-rc2",
              "versionType": "original_commit_for_fix"
            }
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        }
      ],
      "cpeApplicability": [
        {
          "nodes": [
            {
              "cpeMatch": [
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                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "6.6.157",
                  "versionStartIncluding": "6.3",
                  "vulnerable": true
                },
                {
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                  "versionEndExcluding": "6.12.110",
                  "versionStartIncluding": "6.3",
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                },
                {
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              "negate": false,
              "operator": "OR"
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      "descriptions": [
        {
          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nLoongArch: Avoid preempt count underflow without probe\n\nLoongArch uses break 11 for the breakpoint placed after an instruction\nthat Kprobes executes out of line. Since userspace can issue the same\nbreak instruction, do_bp() can reach kprobe_singlestep_handler() when\nthere is no current probe.\n\nThe handler actually returns false in this case, but it first calls\npreempt_enable_no_resched(). The corresponding preempt_disable() is done\nby kprobe_breakpoint_handler() on a real Kprobe hit, so it has not run\nhere. As a result, an ordinary userspace breakpoint (code 11) underflows\nthe current task\u0027s preempt count.\n\nThis also makes in_interrupt() return true until the task schedules. One\nvisible consequence is the socket cgroup attribution: cgroup_sk_alloc()\ntreats the allocation as interrupt context and assigns the socket to the\nroot cgroup. A socket opened from the SIGTRAP handler can then avoid a\nBPF_CGROUP_INET_SOCK_CREATE policy attached to the task\u0027s own cgroup.\n\nReturn as soon as kprobe_running() reports no active probe.\n\nThe same check has appeared in [PATCH v10 2/4] of the original LoongArch\nKprobes series, but was dropped before the feature reached mainline."
        }
      ],
      "metrics": [
        {
          "cvssV3_1": {
            "baseScore": 7.8,
            "baseSeverity": "HIGH",
            "vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H",
            "version": "3.1"
          },
          "scenarios": [
            {
              "lang": "en",
              "value": "AV:L - An unprivileged LoongArch process reaches do_bp() then kprobe_singlestep_handler() by executing break 11 (BRK_KPROBE_SSTEPBP). That is a local CPU exception path, not a network protocol, adjacent wireless/Bluetooth frame, or physical device interface.\nAC:L - With no kprobe running on the CPU (the normal case), break 11 always takes the unmatched preempt_enable_no_resched() path and underflows preempt_count. The attacker then calls socket() from their own SIGTRAP handler; no race or victim-controlled state is required.\nPR:L - do_bp() applies no capability or credential check before dispatching BRK_KPROBE_SSTEPBP. Any unprivileged local user who can run code can issue the instruction; init-namespace root and user-namespace capabilities are not required.\nUI:N - The attacker executes break 11 in their own process and, for the cgroup bypass, installs their own SIGTRAP handler that creates sockets. No other user must mount a filesystem, open a device, or otherwise cooperate.\nS:U - Preempt-count corruption and the resulting socket cgroup/BPF misattribution stay inside the host kernel\u0027s security authority. This is not a KVM/Xen guest-to-host escape or an IOMMU/DMA boundary bypass.\nC:H - cgroup_sk_alloc() treats the underflow as interrupt context and pins the new socket to the root cgroup, so BPF_CGROUP_INET_SOCK_CREATE and later cgroup bind/connect/egress programs on the task\u0027s cgroup do not run. In a container or Cilium-style deployment this bypasses network isolation and can expose protected services.\nI:H - Root-cgroup attribution skips the container\u0027s cgroup BPF socket and traffic hooks for that socket, fully bypassing that access-control policy, while the unmatched preempt_enable corrupts kernel preempt_count used for interrupt and atomic accounting.\nA:H - The underflow makes in_atomic() true, so the next schedule (default SIGTRAP teardown or any blocking syscall) hits BUG: scheduling while atomic and can panic the host, especially with panic_on_warn. mem_cgroup_sk_alloc() also skips container socket charging, allowing host memory exhaustion."
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-09-16T14:39:50.410Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "references": [
        {
          "url": "https://git.kernel.org/stable/c/ff40e597d5d98c0c45a4d09df8177202fac9520e"
        },
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          "url": "https://git.kernel.org/stable/c/a1cb727fa27c2d9c7859729cd90db7bc0f46957f"
        },
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          "url": "https://git.kernel.org/stable/c/76395109a051b53860faaec96522ef08ae9e8e27"
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        {
          "url": "https://git.kernel.org/stable/c/72ce4b24676e8b3b75376c4c559dd81c1ac52d5a"
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      ],
      "title": "LoongArch: Avoid preempt count underflow without probe",
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  "cveMetadata": {
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    "assignerShortName": "Linux",
    "cveId": "CVE-2026-89902",
    "datePublished": "2026-09-16T10:32:01.655Z",
    "dateReserved": "2026-09-11T19:38:34.774Z",
    "dateUpdated": "2026-09-16T14:39:50.410Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2",
  "vulnerability-lookup:meta": {
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      "date": "2026-09-25",
      "epss": "0.00175",
      "percentile": "0.06208"
    },
    "microsoft_vex": {
      "current_release_date": "2026-09-23T02:25:38.000Z",
      "cve": "CVE-2026-89902",
      "id": "msrc_CVE-2026-89902",
      "initial_release_date": "2026-09-17T01:12:18.000Z",
      "product_status:known_affected": "2",
      "source": "Microsoft CSAF VEX",
      "status": "final",
      "title": "LoongArch: Avoid preempt count underflow without probe",
      "url": "https://msrc.microsoft.com/csaf/vex/2026/msrc_cve-2026-89902.json",
      "version": "2"
    },
    "nvd": {
      "cve": {
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                "product": "Linux",
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                "versions": [
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        "cveTags": [],
        "descriptions": [
          {
            "lang": "en",
            "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nLoongArch: Avoid preempt count underflow without probe\n\nLoongArch uses break 11 for the breakpoint placed after an instruction\nthat Kprobes executes out of line. Since userspace can issue the same\nbreak instruction, do_bp() can reach kprobe_singlestep_handler() when\nthere is no current probe.\n\nThe handler actually returns false in this case, but it first calls\npreempt_enable_no_resched(). The corresponding preempt_disable() is done\nby kprobe_breakpoint_handler() on a real Kprobe hit, so it has not run\nhere. As a result, an ordinary userspace breakpoint (code 11) underflows\nthe current task\u0027s preempt count.\n\nThis also makes in_interrupt() return true until the task schedules. One\nvisible consequence is the socket cgroup attribution: cgroup_sk_alloc()\ntreats the allocation as interrupt context and assigns the socket to the\nroot cgroup. A socket opened from the SIGTRAP handler can then avoid a\nBPF_CGROUP_INET_SOCK_CREATE policy attached to the task\u0027s own cgroup.\n\nReturn as soon as kprobe_running() reports no active probe.\n\nThe same check has appeared in [PATCH v10 2/4] of the original LoongArch\nKprobes series, but was dropped before the feature reached mainline."
          }
        ],
        "id": "CVE-2026-89902",
        "lastModified": "2026-09-16T15:18:16.307",
        "metrics": {
          "cvssMetricV31": [
            {
              "cvssData": {
                "attackComplexity": "LOW",
                "attackVector": "LOCAL",
                "availabilityImpact": "HIGH",
                "baseScore": 7.8,
                "baseSeverity": "HIGH",
                "confidentialityImpact": "HIGH",
                "integrityImpact": "HIGH",
                "privilegesRequired": "LOW",
                "scope": "UNCHANGED",
                "userInteraction": "NONE",
                "vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H",
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              "impactScore": 5.9,
              "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
              "type": "Secondary"
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        "published": "2026-09-16T11:16:59.143",
        "references": [
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          },
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          },
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          }
        ],
        "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "vulnStatus": "Received"
      }
    },
    "suse_vex": {
      "aggregate_severity": "moderate",
      "current_release_date": "2026-09-19T23:56:41Z",
      "cve": "CVE-2026-89902",
      "id": "CVE-2026-89902",
      "initial_release_date": "2026-09-19T23:56:41Z",
      "product_status:known_not_affected": "347",
      "source": "SUSE CSAF VEX",
      "status": "interim",
      "title": "SUSE CVE CVE-2026-89902",
      "url": "https://ftp.suse.com/pub/projects/security/csaf-vex/cve-2026-89902.json",
      "version": "2"
    }
  }
}



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