CVE-2026-31584

Description

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.

Gravité et risque d'exploitation

CVE-2026-31584 obtient un score CVSS de 7.8/10, soit une gravité élevée. Selon le modèle EPSS, la probabilité qu'elle soit exploitée dans les 30 prochains jours est de 0.17 %, ce qui la place devant 6.1 % des CVE référencées.

Que faire ?

• Vérifiez si Linux (versions <=7.0.*, <=6.12.*, <f1692337c6fa26e04f89b22a4d84bf5b7ada50d1, 0, 6.12.83, 7.0.1, <9a9bdaf9dc42ccca50e53f82165292f74a365c11, <6.6, <f99353cd0e9f58bf17889049137b8d65fb44ebf1, <76e35091ffc722ba39b303e48bc5d08abb59dd56, <=6.6.*, <=6.19.*, 6.6.136, <a8a55913552aed45108525d1851c65e1db0cc25b, 6.6, 7.1, <=6.18.*, <=*, 6.19.14, <93d9a58961a9e09306857e999b3ee76aa4be67f0, 0934d37596151edce115c6d0843a9ad7d5e5d232, 6.18.24) est présent sur votre parc.
• Appliquez le correctif ou la version corrigée indiqués dans les références de l'éditeur.
• À défaut de correctif, limitez l'exposition (filtrage réseau, désactivation du composant).
• Automatisez la détection : les agents CVE Heimdall (gratuits, open source) corrèlent l'inventaire de vos serveurs avec la base CVE.

Références

• https://git.kernel.org/stable/c/9a9bdaf9dc42ccca50e53f82165292f74a365c11
• https://git.kernel.org/stable/c/a8a55913552aed45108525d1851c65e1db0cc25b
• https://git.kernel.org/stable/c/f99353cd0e9f58bf17889049137b8d65fb44ebf1
• https://git.kernel.org/stable/c/93d9a58961a9e09306857e999b3ee76aa4be67f0
• https://git.kernel.org/stable/c/f1692337c6fa26e04f89b22a4d84bf5b7ada50d1
• https://git.kernel.org/stable/c/76e35091ffc722ba39b303e48bc5d08abb59dd56