{ "dataType": "CVE_RECORD", "dataVersion": "5.2", "cveMetadata": { "cveId": "CVE-2026-89902", "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "state": "PUBLISHED", "assignerShortName": "Linux", "dateReserved": "2026-09-11T19:38:34.774Z", "datePublished": "2026-09-16T10:32:01.655Z", "dateUpdated": "2026-10-19T08:54:35.100Z" }, "containers": { "cna": { "providerMetadata": { "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "shortName": "Linux", "dateUpdated": "2026-10-19T08:54:35.100Z" }, "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's 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's 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": { "version": "3.1", "vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H", "baseScore": 7.8, "baseSeverity": "HIGH" }, "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's 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's 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's 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." } ] } ], "affected": [ { "product": "Linux", "vendor": "Linux", "defaultStatus": "unaffected", "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git", "programFiles": [ "arch/loongarch/kernel/kprobes.c" ], "versions": [ { "version": "6d4cc40fb5f58147defc6c0e9d86e6232fe31616", "lessThan": "ff40e597d5d98c0c45a4d09df8177202fac9520e", "status": "affected", "versionType": "git" }, { "version": "6d4cc40fb5f58147defc6c0e9d86e6232fe31616", "lessThan": "a1cb727fa27c2d9c7859729cd90db7bc0f46957f", "status": "affected", "versionType": "git" }, { "version": "6d4cc40fb5f58147defc6c0e9d86e6232fe31616", "lessThan": "76395109a051b53860faaec96522ef08ae9e8e27", "status": "affected", "versionType": "git" }, { "version": "6d4cc40fb5f58147defc6c0e9d86e6232fe31616", "lessThan": "c4357ebeee63cb8da1446fc936573a34e68b0f71", "status": "affected", "versionType": "git" }, { "version": "6d4cc40fb5f58147defc6c0e9d86e6232fe31616", "lessThan": "72ce4b24676e8b3b75376c4c559dd81c1ac52d5a", "status": "affected", "versionType": "git" } ] }, { "product": "Linux", "vendor": "Linux", "defaultStatus": "affected", "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git", "programFiles": [ "arch/loongarch/kernel/kprobes.c" ], "versions": [ { "version": "6.3", "status": "affected" }, { "version": "0", "lessThan": "6.3", "status": "unaffected", "versionType": "semver" }, { "version": "6.6.157", "lessThanOrEqual": "6.6.*", "status": "unaffected", "versionType": "semver" }, { "version": "6.12.110", "lessThanOrEqual": "6.12.*", "status": "unaffected", "versionType": "semver" }, { "version": "6.18.51", "lessThanOrEqual": "6.18.*", "status": "unaffected", "versionType": "semver" }, { "version": "7.2.5", "lessThanOrEqual": "7.2.*", "status": "unaffected", "versionType": "semver" }, { "version": "7.3", "lessThanOrEqual": "*", "status": "unaffected", "versionType": "original_commit_for_fix" } ] } ], "cpeApplicability": [ { "nodes": [ { "operator": "OR", "negate": false, "cpeMatch": [ { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.3", "versionEndExcluding": "6.6.157" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.3", "versionEndExcluding": "6.12.110" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.3", "versionEndExcluding": "6.18.51" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.3", "versionEndExcluding": "7.2.5" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.3", "versionEndExcluding": "7.3" } ] } ] } ], "references": [ { "url": "https://git.kernel.org/stable/c/ff40e597d5d98c0c45a4d09df8177202fac9520e" }, { "url": "https://git.kernel.org/stable/c/a1cb727fa27c2d9c7859729cd90db7bc0f46957f" }, { "url": "https://git.kernel.org/stable/c/76395109a051b53860faaec96522ef08ae9e8e27" }, { "url": "https://git.kernel.org/stable/c/c4357ebeee63cb8da1446fc936573a34e68b0f71" }, { "url": "https://git.kernel.org/stable/c/72ce4b24676e8b3b75376c4c559dd81c1ac52d5a" } ], "title": "LoongArch: Avoid preempt count underflow without probe", "x_generator": { "engine": "bippy-1.2.0" } } } }