FKIE_CVE-2026-98644

Vulnerability from fkie_nvd - Published: 2026-10-18 16:17 - Updated: 2026-10-19 10:19
Severity
Summary
In the Linux kernel, the following vulnerability has been resolved: bpf: Avoid soft lockup in __htab_map_lookup_and_delete_batch() __htab_map_lookup_and_delete_batch() has no rescheduling point. The batch count bounds how many entries are copied out, not how many buckets are visited, so one BPF_MAP_LOOKUP_BATCH call can walk the map end to end. The empty-bucket fast path is worse: it stays inside a single rcu_read_lock() / bpf_disable_instrumentation() section for any run of consecutive empty buckets. That holds up on small maps, but it falls apart at scale. On a 144-CPU arm64 host running a CONFIG_PREEMPT_NONE kernel, periodic BPF_MAP_LOOKUP_BATCH calls against an LRU hash map with 16,777,216 buckets held a CPU inside the batch op for 77+ seconds and triggered the soft lockup watchdog. Commit 75134f16e7dd ("bpf: Add schedule points in batch ops") fixed this same problem in the generic batch ops, but not in this htab-native path, which every htab-based hash map variant uses for its lookup[_and_delete] batch ops. Complete that fix here. Leave the critical section after 64 consecutive empty buckets, call cond_resched_tasks_rcu_qs(), and resume at the saved bucket cursor. No locks are held at that point, and resuming from the cursor is already the function's behavior for non-empty buckets. Add the same call to the per-bucket loop after copy_to_user(), where every lock has been dropped. cond_resched_rcu() is not enough here: sleeping with bpf_prog_active elevated makes tracing programs on that CPU silently skip their invocations. Plain cond_resched() is not enough either. It is a no-op under PREEMPT and PREEMPT_LAZY, the only models arm64 and x86 have offered since commit 7dadeaa6e851 ("sched: Further restrict the preemption modes"). It is also never a Tasks RCU quiescent state, in any model: the reschedule counts as a preemption. The walking task stays a holdout and stalls every synchronize_rcu_tasks() caller, ftrace and BPF trampoline teardown included, until the syscall returns [1]. cond_resched_tasks_rcu_qs() is the usual tool for that [2]. It reports the quiescent state at each yield and still reschedules as cond_resched() does on PREEMPT_NONE and PREEMPT_VOLUNTARY kernels.
References
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/44f9bcb5ab2b268bc763ed3ebec83308b4972936
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/4e48fe9b1c77966bede0a73feb3059d7595f642d
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/5c8b1869cb99a32a962388848cd19604fb41263e
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/77a3b52b4455e6377e549539e757bc55eedefb51
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/85136bf22404474a815fc0ed26ec0d1cbc1bc3f9
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/ca5bd55fc508fbb5c08c62206d02237a5b6fc7e8
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/f0c09de08ec077098b7e1563f2285f1c136cd816
Impacted products
Vendor Product Version
To clipboard 

{
  "affected": [
    {
      "affectedData": [
        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "kernel/bpf/hashtab.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
            {
              "lessThan": "5c8b1869cb99a32a962388848cd19604fb41263e",
              "status": "affected",
              "version": "057996380a42bb64ccc04383cfa9c0ace4ea11f0",
              "versionType": "git"
            },
            {
              "lessThan": "ca5bd55fc508fbb5c08c62206d02237a5b6fc7e8",
              "status": "affected",
              "version": "057996380a42bb64ccc04383cfa9c0ace4ea11f0",
              "versionType": "git"
            },
            {
              "lessThan": "77a3b52b4455e6377e549539e757bc55eedefb51",
              "status": "affected",
              "version": "057996380a42bb64ccc04383cfa9c0ace4ea11f0",
              "versionType": "git"
            },
            {
              "lessThan": "f0c09de08ec077098b7e1563f2285f1c136cd816",
              "status": "affected",
              "version": "057996380a42bb64ccc04383cfa9c0ace4ea11f0",
              "versionType": "git"
            },
            {
              "lessThan": "44f9bcb5ab2b268bc763ed3ebec83308b4972936",
              "status": "affected",
              "version": "057996380a42bb64ccc04383cfa9c0ace4ea11f0",
              "versionType": "git"
            },
            {
              "lessThan": "4e48fe9b1c77966bede0a73feb3059d7595f642d",
              "status": "affected",
              "version": "057996380a42bb64ccc04383cfa9c0ace4ea11f0",
              "versionType": "git"
            },
            {
              "lessThan": "85136bf22404474a815fc0ed26ec0d1cbc1bc3f9",
              "status": "affected",
              "version": "057996380a42bb64ccc04383cfa9c0ace4ea11f0",
              "versionType": "git"
            }
          ]
        },
        {
          "defaultStatus": "affected",
          "product": "Linux",
          "programFiles": [
            "kernel/bpf/hashtab.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
            {
              "status": "affected",
              "version": "5.6"
            },
            {
              "lessThan": "5.6",
              "status": "unaffected",
              "version": "0",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "5.15.*",
              "status": "unaffected",
              "version": "5.15.222",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.1.*",
              "status": "unaffected",
              "version": "6.1.189",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.6.*",
              "status": "unaffected",
              "version": "6.6.158",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.12.*",
              "status": "unaffected",
              "version": "6.12.112",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.18.*",
              "status": "unaffected",
              "version": "6.18.55",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "7.2.*",
              "status": "unaffected",
              "version": "7.2.9",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "*",
              "status": "unaffected",
              "version": "7.3",
              "versionType": "original_commit_for_fix"
            }
          ]
        }
      ],
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
    }
  ],
  "cveTags": [],
  "descriptions": [
    {
      "lang": "en",
      "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nbpf: Avoid soft lockup in __htab_map_lookup_and_delete_batch()\n\n__htab_map_lookup_and_delete_batch() has no rescheduling point. The\nbatch count bounds how many entries are copied out, not how many\nbuckets are visited, so one BPF_MAP_LOOKUP_BATCH call can walk the\nmap end to end. The empty-bucket fast path is worse: it stays inside\na single rcu_read_lock() / bpf_disable_instrumentation() section for\nany run of consecutive empty buckets.\n\nThat holds up on small maps, but it falls apart at scale. On a\n144-CPU arm64 host running a CONFIG_PREEMPT_NONE kernel, periodic\nBPF_MAP_LOOKUP_BATCH calls against an LRU hash map with 16,777,216\nbuckets held a CPU inside the batch op for 77+ seconds and triggered\nthe soft lockup watchdog.\n\nCommit 75134f16e7dd (\"bpf: Add schedule points in batch ops\") fixed this\nsame problem in the generic batch ops, but not in this htab-native path,\nwhich every htab-based hash map variant uses for its lookup[_and_delete]\nbatch ops.\n\nComplete that fix here. Leave the critical section after 64 consecutive\nempty buckets, call cond_resched_tasks_rcu_qs(), and resume at the saved\nbucket cursor. No locks are held at that point, and resuming from the\ncursor is already the function\u0027s behavior for non-empty buckets. Add the\nsame call to the per-bucket loop after copy_to_user(), where every lock\nhas been dropped. cond_resched_rcu() is not enough here: sleeping with\nbpf_prog_active elevated makes tracing programs on that CPU silently\nskip their invocations.\n\nPlain cond_resched() is not enough either. It is a no-op under PREEMPT\nand PREEMPT_LAZY, the only models arm64 and x86 have offered since\ncommit 7dadeaa6e851 (\"sched: Further restrict the preemption modes\").\nIt is also never a Tasks RCU quiescent state, in any model: the\nreschedule counts as a preemption. The walking task stays a holdout and\nstalls every synchronize_rcu_tasks() caller, ftrace and BPF trampoline\nteardown included, until the syscall returns [1].\ncond_resched_tasks_rcu_qs() is the usual tool for that [2]. It reports\nthe quiescent state at each yield and still reschedules as\ncond_resched() does on PREEMPT_NONE and PREEMPT_VOLUNTARY kernels."
    }
  ],
  "id": "CVE-2026-98644",
  "lastModified": "2026-10-19T10:19:28.723",
  "metrics": {},
  "published": "2026-10-18T16:17:17.623",
  "references": [
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/44f9bcb5ab2b268bc763ed3ebec83308b4972936"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/4e48fe9b1c77966bede0a73feb3059d7595f642d"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/5c8b1869cb99a32a962388848cd19604fb41263e"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/77a3b52b4455e6377e549539e757bc55eedefb51"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/85136bf22404474a815fc0ed26ec0d1cbc1bc3f9"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/ca5bd55fc508fbb5c08c62206d02237a5b6fc7e8"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/f0c09de08ec077098b7e1563f2285f1c136cd816"
    }
  ],
  "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
  "vulnStatus": "Received"
}



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