{"id":"CVE-2026-31584","summary":"media: mediatek: vcodec: fix use-after-free in encoder release path","details":"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, &ctx-\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(&ctx-\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(&ctx-\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.","modified":"2026-06-24T18:29:23.226848645Z","published":"2026-04-24T14:42:13.586Z","related":["CGA-624h-xfm2-g54m","SUSE-SU-2026:22099-1","SUSE-SU-2026:22112-1","SUSE-SU-2026:22127-1","openSUSE-SU-2026:10703-1","openSUSE-SU-2026:20965-1"],"database_specific":{"cna_assigner":"Linux","osv_generated_from":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/31xxx/CVE-2026-31584.json"},"references":[{"type":"WEB","url":"https://git.kernel.org/stable/c/76e35091ffc722ba39b303e48bc5d08abb59dd56"},{"type":"WEB","url":"https://git.kernel.org/stable/c/93d9a58961a9e09306857e999b3ee76aa4be67f0"},{"type":"WEB","url":"https://git.kernel.org/stable/c/9a9bdaf9dc42ccca50e53f82165292f74a365c11"},{"type":"WEB","url":"https://git.kernel.org/stable/c/a8a55913552aed45108525d1851c65e1db0cc25b"},{"type":"WEB","url":"https://git.kernel.org/stable/c/f1692337c6fa26e04f89b22a4d84bf5b7ada50d1"},{"type":"WEB","url":"https://git.kernel.org/stable/c/f99353cd0e9f58bf17889049137b8d65fb44ebf1"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/31xxx/CVE-2026-31584.json"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-31584"},{"type":"PACKAGE","url":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git"}],"affected":[{"ranges":[{"type":"GIT","repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","events":[{"introduced":"0934d37596151edce115c6d0843a9ad7d5e5d232"},{"fixed":"9a9bdaf9dc42ccca50e53f82165292f74a365c11"},{"fixed":"a8a55913552aed45108525d1851c65e1db0cc25b"},{"fixed":"f99353cd0e9f58bf17889049137b8d65fb44ebf1"},{"fixed":"93d9a58961a9e09306857e999b3ee76aa4be67f0"},{"fixed":"f1692337c6fa26e04f89b22a4d84bf5b7ada50d1"},{"fixed":"76e35091ffc722ba39b303e48bc5d08abb59dd56"}]}],"database_specific":{"source":"https://storage.googleapis.com/osv-test-cve-osv-conversion/osv-output/CVE-2026-31584.json"}},{"package":{"name":"Kernel","ecosystem":"Linux"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"6.6.0"},{"fixed":"6.6.136"}]},{"type":"ECOSYSTEM","events":[{"introduced":"6.7.0"},{"fixed":"6.12.83"}]},{"type":"ECOSYSTEM","events":[{"introduced":"6.13.0"},{"fixed":"6.18.24"}]},{"type":"ECOSYSTEM","events":[{"introduced":"6.19.0"},{"fixed":"6.19.14"}]},{"type":"ECOSYSTEM","events":[{"introduced":"6.20.0"},{"fixed":"7.0.1"}]}],"database_specific":{"source":"https://storage.googleapis.com/osv-test-cve-osv-conversion/osv-output/CVE-2026-31584.json"}}],"schema_version":"1.7.5","severity":[{"type":"CVSS_V3","score":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H"}]}