CVE-2026-31584 (GCVE-0-2026-31584)
Vulnerability from cvelistv5
Published
2026-04-24 14:42
Modified
2026-08-05 12:23
Severity ?
7.8 (High) - CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
Summary
In the Linux kernel, the following vulnerability has been resolved: media: mediatek: vcodec: fix use-after-free in encoder release path The fops_vcodec_release() function frees the context structure (ctx) without first cancelling any pending or running work in ctx->encode_work. This creates a race window where the workqueue handler (mtk_venc_worker) may still be accessing the context memory after it has been freed. Race condition: CPU 0 (release path) CPU 1 (workqueue) --------------------- ------------------ fops_vcodec_release() v4l2_m2m_ctx_release() v4l2_m2m_cancel_job() // waits for m2m job "done" mtk_venc_worker() v4l2_m2m_job_finish() // m2m job "done" // BUT worker still running! // post-job_finish access: other ctx dereferences // UAF if ctx already freed // returns (job "done") kfree(ctx) // ctx freed Root cause: The v4l2_m2m_ctx_release() only waits for the m2m job lifecycle (via TRANS_RUNNING flag), not the workqueue lifecycle. After v4l2_m2m_job_finish() is called, the m2m framework considers the job complete and v4l2_m2m_ctx_release() returns, but the worker function continues executing and may still access ctx. The work is queued during encode operations via: queue_work(ctx->dev->encode_workqueue, &ctx->encode_work) The worker function accesses ctx->m2m_ctx, ctx->dev, and other ctx fields even after calling v4l2_m2m_job_finish(). This vulnerability was confirmed with KASAN by running an instrumented test module that widens the post-job_finish race window. KASAN detected: BUG: KASAN: slab-use-after-free in mtk_venc_worker+0x159/0x180 Read of size 4 at addr ffff88800326e000 by task kworker/u8:0/12 Workqueue: mtk_vcodec_enc_wq mtk_venc_worker Allocated by task 47: __kasan_kmalloc+0x7f/0x90 fops_vcodec_open+0x85/0x1a0 Freed by task 47: __kasan_slab_free+0x43/0x70 kfree+0xee/0x3a0 fops_vcodec_release+0xb7/0x190 Fix this by calling cancel_work_sync(&ctx->encode_work) before kfree(ctx). This ensures the workqueue handler is both cancelled (if pending) and synchronized (waits for any running handler to complete) before the context is freed. Placement rationale: The fix is placed after v4l2_ctrl_handler_free() and before list_del_init(&ctx->list). At this point, all m2m operations are done (v4l2_m2m_ctx_release() has returned), and we need to ensure the workqueue is synchronized before removing ctx from the list and freeing it. Note: The open error path does NOT need cancel_work_sync() because INIT_WORK() only initializes the work structure - it does not schedule it. Work is only scheduled later during device_run() operations.
References
Impacted products
Vendor Product Version
Linux Linux Version: 0934d37596151edce115c6d0843a9ad7d5e5d232
Version: 0934d37596151edce115c6d0843a9ad7d5e5d232
Version: 0934d37596151edce115c6d0843a9ad7d5e5d232
Version: 0934d37596151edce115c6d0843a9ad7d5e5d232
Version: 0934d37596151edce115c6d0843a9ad7d5e5d232
Version: 0934d37596151edce115c6d0843a9ad7d5e5d232
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{
  "containers": {
    "cna": {
      "affected": [
        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "drivers/media/platform/mediatek/vcodec/encoder/mtk_vcodec_enc_drv.c"
          ],
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        {
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          "product": "Linux",
          "programFiles": [
            "drivers/media/platform/mediatek/vcodec/encoder/mtk_vcodec_enc_drv.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
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              "version": "7.0.1",
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            },
            {
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              "status": "unaffected",
              "version": "7.1",
              "versionType": "original_commit_for_fix"
            }
          ]
        }
      ],
      "cpeApplicability": [
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          "nodes": [
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                  "vulnerable": true
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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\nmedia: mediatek: vcodec: fix use-after-free in encoder release path\n\nThe fops_vcodec_release() function frees the context structure (ctx)\nwithout first cancelling any pending or running work in ctx-\u003eencode_work.\nThis creates a race window where the workqueue handler (mtk_venc_worker)\nmay still be accessing the context memory after it has been freed.\n\nRace condition:\n\n    CPU 0 (release path)               CPU 1 (workqueue)\n    ---------------------               ------------------\n    fops_vcodec_release()\n      v4l2_m2m_ctx_release()\n        v4l2_m2m_cancel_job()\n        // waits for m2m job \"done\"\n                                        mtk_venc_worker()\n                                          v4l2_m2m_job_finish()\n                                          // m2m job \"done\"\n                                          // BUT worker still running!\n                                          // post-job_finish access:\n                                        other ctx dereferences\n                                          // UAF if ctx already freed\n        // returns (job \"done\")\n      kfree(ctx)  // ctx freed\n\nRoot cause: The v4l2_m2m_ctx_release() only waits for the m2m job\nlifecycle (via TRANS_RUNNING flag), not the workqueue lifecycle.\nAfter v4l2_m2m_job_finish() is called, the m2m framework considers\nthe job complete and v4l2_m2m_ctx_release() returns, but the worker\nfunction continues executing and may still access ctx.\n\nThe work is queued during encode operations via:\n  queue_work(ctx-\u003edev-\u003eencode_workqueue, \u0026ctx-\u003eencode_work)\nThe worker function accesses ctx-\u003em2m_ctx, ctx-\u003edev, and other ctx\nfields even after calling v4l2_m2m_job_finish().\n\nThis vulnerability was confirmed with KASAN by running an instrumented\ntest module that widens the post-job_finish race window. KASAN detected:\n\n  BUG: KASAN: slab-use-after-free in mtk_venc_worker+0x159/0x180\n  Read of size 4 at addr ffff88800326e000 by task kworker/u8:0/12\n\n  Workqueue: mtk_vcodec_enc_wq mtk_venc_worker\n\n  Allocated by task 47:\n    __kasan_kmalloc+0x7f/0x90\n    fops_vcodec_open+0x85/0x1a0\n\n  Freed by task 47:\n    __kasan_slab_free+0x43/0x70\n    kfree+0xee/0x3a0\n    fops_vcodec_release+0xb7/0x190\n\nFix this by calling cancel_work_sync(\u0026ctx-\u003eencode_work) before kfree(ctx).\nThis ensures the workqueue handler is both cancelled (if pending) and\nsynchronized (waits for any running handler to complete) before the\ncontext is freed.\n\nPlacement rationale: The fix is placed after v4l2_ctrl_handler_free()\nand before list_del_init(\u0026ctx-\u003elist). At this point, all m2m operations\nare done (v4l2_m2m_ctx_release() has returned), and we need to ensure\nthe workqueue is synchronized before removing ctx from the list and\nfreeing it.\n\nNote: The open error path does NOT need cancel_work_sync() because\nINIT_WORK() only initializes the work structure - it does not schedule\nit. Work is only scheduled later during device_run() operations."
        }
      ],
      "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 - The vulnerable path is reached through local V4L2 character device operations on the MediaTek mem2mem encoder, ending in `fops_vcodec_release()` after encode work is queued. It is not reachable directly by network packets or adjacent/physical input.\nAC:L - The attacker can queue encoder work with standard V4L2 ioctls and then close the same device while the workqueue handler is running. The race is attacker-driven and can be retried, so there are no external conditions that justify high complexity.\nPR:L - Triggering requires local access to the registered `/dev/video*` encoder node, but the driver and V4L2 core path contain no `capable()` or administrator-only checks. A basic local user with normal device-node access can reach the vulnerable ioctl/release path.\nUI:N - No victim action is required once the attacker can run code locally and access the video encoder device. The attacker controls the open, buffer queueing, streaming, and close operations.\nS:U - The vulnerability is in a kernel driver and impacts the same OS/kernel security authority. It does not cross a VM, hypervisor, IOMMU, or other separate security scope boundary.\nC:H - This is a slab use-after-free of the encoder context after `v4l2_m2m_job_finish()` lets release free the context while `mtk_venc_worker` can still dereference it. A kernel UAF is defensibly treated as enabling high confidentiality impact through heap reuse and memory disclosure primitives.\nI:H - The freed context contains pointers and state used by the worker, and UAF exploitation can be shaped with heap reuse to corrupt kernel control/data flow. Following the required overestimation rule for UAFs, integrity impact is high.\nA:H - KASAN confirmed a slab-use-after-free in `mtk_venc_worker`, and even non-exploited triggering can produce kernel oops/panic or destabilize the encoder workqueue path. Repeated local triggering can therefore cause high availability impact."
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-08-05T12:23:36.030Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "references": [
        {
          "url": "https://git.kernel.org/stable/c/9a9bdaf9dc42ccca50e53f82165292f74a365c11"
        },
        {
          "url": "https://git.kernel.org/stable/c/a8a55913552aed45108525d1851c65e1db0cc25b"
        },
        {
          "url": "https://git.kernel.org/stable/c/f99353cd0e9f58bf17889049137b8d65fb44ebf1"
        },
        {
          "url": "https://git.kernel.org/stable/c/93d9a58961a9e09306857e999b3ee76aa4be67f0"
        },
        {
          "url": "https://git.kernel.org/stable/c/f1692337c6fa26e04f89b22a4d84bf5b7ada50d1"
        },
        {
          "url": "https://git.kernel.org/stable/c/76e35091ffc722ba39b303e48bc5d08abb59dd56"
        }
      ],
      "title": "media: mediatek: vcodec: fix use-after-free in encoder release path",
      "x_generator": {
        "engine": "bippy-1.2.0"
      }
    }
  },
  "cveMetadata": {
    "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
    "assignerShortName": "Linux",
    "cveId": "CVE-2026-31584",
    "datePublished": "2026-04-24T14:42:13.586Z",
    "dateReserved": "2026-03-09T15:48:24.120Z",
    "dateUpdated": "2026-08-05T12:23:36.030Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}


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