Description

In the Linux kernel, the following vulnerability has been resolved: misc: fastrpc: fix use-after-free of fastrpc_user in workqueue context There is a race between fastrpc_device_release() and the workqueue that processes DSP responses. When the user closes the file descriptor, fastrpc_device_release() frees the fastrpc_user structure. Concurrently, an in-flight DSP invocation can complete and fastrpc_rpmsg_callback() schedules context cleanup via schedule_work(&ctx->put_work). If the workqueue runs fastrpc_context_free() in parallel with or after fastrpc_device_release() has freed the user structure, it dereferences the freed fastrpc_user. Depending on the state of the context at the time of the race, any one of the following accesses can be hit: 1. fastrpc_buf_free() calls fastrpc_ipa_to_dma_addr(buf->fl->cctx, ...) to strip the SID bits from the stored IOVA before passing the physical address to dma_free_coherent(). 2. fastrpc_free_map() reads map->fl->cctx->vmperms[0].vmid to reconstruct the source permission bitmask needed for the qcom_scm_assign_mem() call that returns memory from the DSP VM back to HLOS. 3. fastrpc_free_map() acquires map->fl->lock to safely remove the map node from the fl->maps list. The resulting use-after-free manifests as: pc : fastrpc_buf_free+0x38/0x80 [fastrpc] lr : fastrpc_context_free+0xa8/0x1b0 [fastrpc] fastrpc_context_free+0xa8/0x1b0 [fastrpc] fastrpc_context_put_wq+0x78/0xa0 [fastrpc] process_one_work+0x180/0x450 worker_thread+0x26c/0x388 Add kref-based reference counting to fastrpc_user. Have each invoke context take a reference on the user at allocation time and release it when the context is freed. Release the initial reference in fastrpc_device_release() at file close. Move the teardown of the user structure — freeing pending contexts, maps, mmaps, and the channel context reference — into the kref release callback fastrpc_user_free(), so that it runs only when the last reference is dropped, regardless of whether that happens at device close or after the final in-flight context completes.

Predictions

Heuristic predictions, AS-IS, for prioritization only.

Mitigations

https://git.kernel.org/linus/e85eb5feca8e254905ffa6c57a3c99c89a674a0f (7.1)

https://git.kernel.org/linus/e85eb5feca8e254905ffa6c57a3c99c89a674a0f (7.1)

References

• https://git.kernel.org/stable/c/c6e5c2be09f814377d7f1ce97370a5b7b3e02814
• https://git.kernel.org/stable/c/e1e3a05efe5954d5bad01157d79429d39a67a7ae
• https://git.kernel.org/stable/c/d42679eef34dd590b694ce3b666c5e2ba10cd4bf
• https://git.kernel.org/stable/c/df08fadcf0e5f3708365ec3b6d30b5aafd98bea1
• https://git.kernel.org/stable/c/ecea4967c2bff92c2fafbc59893f711b39f7b152
• https://git.kernel.org/stable/c/5278ccd357e0d7aeeb1e76c0f3e0e02894a9897c
• https://git.kernel.org/stable/c/fbe0947420eec18a84638d29468c2d563ce4e6a3
• https://git.kernel.org/stable/c/e85eb5feca8e254905ffa6c57a3c99c89a674a0f
• https://security-tracker.debian.org/tracker/CVE-2026-53161