CVE-2026-31584 (GCVE-0-2026-31584)

Vulnerability from cvelistv5 – Published: 2026-04-24 14:42 – Updated: 2026-04-27 14:04
VLAI?
Title
media: mediatek: vcodec: fix use-after-free in encoder release path
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.
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
Linux Linux Affected: 0934d37596151edce115c6d0843a9ad7d5e5d232 , < 9a9bdaf9dc42ccca50e53f82165292f74a365c11 (git)
Affected: 0934d37596151edce115c6d0843a9ad7d5e5d232 , < a8a55913552aed45108525d1851c65e1db0cc25b (git)
Affected: 0934d37596151edce115c6d0843a9ad7d5e5d232 , < f99353cd0e9f58bf17889049137b8d65fb44ebf1 (git)
Affected: 0934d37596151edce115c6d0843a9ad7d5e5d232 , < 93d9a58961a9e09306857e999b3ee76aa4be67f0 (git)
Affected: 0934d37596151edce115c6d0843a9ad7d5e5d232 , < f1692337c6fa26e04f89b22a4d84bf5b7ada50d1 (git)
Affected: 0934d37596151edce115c6d0843a9ad7d5e5d232 , < 76e35091ffc722ba39b303e48bc5d08abb59dd56 (git)
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    Linux Linux Affected: 6.6
Unaffected: 0 , < 6.6 (semver)
Unaffected: 6.6.136 , ≤ 6.6.* (semver)
Unaffected: 6.12.83 , ≤ 6.12.* (semver)
Unaffected: 6.18.24 , ≤ 6.18.* (semver)
Unaffected: 6.19.14 , ≤ 6.19.* (semver)
Unaffected: 7.0.1 , ≤ 7.0.* (semver)
Unaffected: 7.1-rc1 , ≤ * (original_commit_for_fix)
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          "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."
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    "dateReserved": "2026-03-09T15:48:24.120Z",
    "dateUpdated": "2026-04-27T14:04:10.188Z",
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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. 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}


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  • Seen: The vulnerability was mentioned, discussed, or observed by the user.
  • Confirmed: The vulnerability has been validated from an analyst's perspective.
  • Published Proof of Concept: A public proof of concept is available for this vulnerability.
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