CVE-2025-38687 — comedi: fix race between polling and detaching

Affected: Linux, Siemens SIMATIC CN 4100

In the Linux kernel, the following vulnerability has been resolved:

comedi: fix race between polling and detaching

syzbot reports a use-after-free in comedi in the below link, which is due to comedi gladly removing the allocated async area even though poll requests are still active on the wait_queue_head inside of it. This can cause a use-after-free when the poll entries are later triggered or removed, as the memory for the wait_queue_head has been freed. We need to check there are no tasks queued on any of the subdevices' wait queues before allowing the device to be detached by the `COMEDI_DEVCONFIG` ioctl.

Tasks will read-lock `dev->attach_lock` before adding themselves to the subdevice wait queue, so fix the problem in the `COMEDI_DEVCONFIG` ioctl handler by write-locking `dev->attach_lock` before checking that all of the subdevices are safe to be deleted. This includes testing for any sleepers on the subdevices' wait queues. It remains locked until the device has been detached. This requires the `comedi_device_detach()` function to be refactored slightly, moving the bulk of it into new function `comedi_device_detach_locked()`.

Note that the refactor of `comedi_device_detach()` results in `comedi_device_cancel_all()` now being called while `dev->attach_lock` is write-locked, which wasn't the case previously, but that does not matter.

Thanks to Jens Axboe for diagnosing the problem and co-developing this patch.

USN-7909-1 — linux, linux-aws, linux-aws-5.15, linux-gcp-5.15, linux-hwe-5.15, linux-ibm, linux-ibm-5.15, linux-intel-iotg, linux-in…

Affected: Ubuntu:Pro:20.04:LTS: linux-aws-5.15, Ubuntu:Pro:20.04:LTS: linux-gcp-5.15, Ubuntu:Pro:20.04:LTS: linux-hwe-5.15, Ubuntu:Pro:20.04:LTS: linux-ibm-5.15, Ubuntu:Pro:20.04:LTS: linux-intel-iotg-5.15, Ubuntu:Pro:20.04:LTS: linux-lowlatency-hwe-5.15, Ubuntu:Pro:20.04:LTS: linux-nvidia-tegra-5.15, Ubuntu:Pro:20.04:LTS: linux-oracle-5.15, Ubuntu:22.04:LTS: linux, Ubuntu:22.04:LTS: linux-aws and 8 more

Several security issues were discovered in the Linux kernel. An attacker could possibly use these to compromise the system. This update corrects flaws in the following subsystems: - ARM32 architecture; - ARM64 architecture; - MIPS architecture; - PowerPC architecture; - RISC-V architecture; - S390 architecture; - x86 architecture; - Block layer subsystem; - ACPI drivers; - ATM drivers; - DRBD Distributed Replicated Block Device drivers; - Bus devices; - Clock framework and drivers; - Data acquisition framework and drivers; - Hardware crypto device drivers; - Device frequency scaling framework; - Buffer Sharing and Synchronization framework; - DMA engine subsystem; - ARM SCMI message protocol; - GPU drivers; - HID subsystem; - Hardware monitoring drivers; - I2C subsystem; - I3C subsystem; - IIO subsystem; - InfiniBand drivers; - Input Device core drivers; - IOMMU subsystem; - Media drivers; - Network drivers; - Mellanox network drivers; - PCI subsystem; - PCCARD (PCMCIA/CardBus) bus subsystem; - PHY drivers; - Power supply drivers; - Voltage and Current Regulator drivers; - SCSI subsystem; - ASPEED SoC drivers; - QCOM SoC drivers; - small TFT LCD display modules; - Trusted Execution Environment drivers; - TTY drivers; - UFS subsystem; - USB core drivers; - DesignWare USB3 driver; - USB Gadget drivers; - Framebuffer layer; - BTRFS file system; - File systems infrastructure; - EF…

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CVE-2025-38687 — comedi: fix race between polling and detaching

USN-7909-1 — linux, linux-aws, linux-aws-5.15, linux-gcp-5.15, linux-hwe-5.15, linux-ibm, linux-ibm-5.15, linux-intel-iotg, linux-in…