UBUNTU-CVE-2025-68257: Null Pointer Dereference
In the Linux kernel, the following vulnerability has been resolved: comedi: check device's attached status in compat ioctls Syzbot identified an issue [1] that crashes kernel, seemingly due to unexistent callback dev->getvalidroutes(). By all means, this should not occur as said callback must always be set to getzerovalidroutes() in comedidevicepostconfig(). As the crash seems to appear exclusively in i386 kernels, at least, judging from [1] reports, the blame lies with compat versions of standard IOCTL handlers. Several of them are modified and do not use comediunlockedioctl(). While functionality of these ioctls essentially copy their original versions, they do not have required sanity check for device's attached status. This, in turn, leads to a possibility of calling select IOCTLs on a device that has not been properly setup, even via COMEDIDEVCONFIG. Doing so on unconfigured devices means that several crucial steps are missed, for instance, specifying dev->getvalidroutes() callback. Fix this somewhat crudely by ensuring device's attached status before performing any ioctls, improving logic consistency between modern and compat functions. [1] Syzbot report: BUG: kernel NULL pointer dereference, address: 0000000000000000 ... CR2: ffffffffffffffd6 CR3: 000000006c717000 CR4: 0000000000352ef0 Call Trace: <TASK> getvalidroutes drivers/comedi/comedifops.c:1322 [inline] parseinsn+0x78c/0x1970 drivers/comedi/comedifops.c:1401 doinsnlistioctl+0x272/0x700 drivers/comedi/comedifops.c:1594 compatinsnlist drivers/comedi/comedifops.c:3208 [inline] comedicompatioctl+0x810/0x990 drivers/comedi/comedifops.c:3273 docompatsysioctl fs/ioctl.c:695 [inline] secompatsysioctl fs/ioctl.c:638 [inline] ia32compatsysioctl+0x242/0x370 fs/ioctl.c:638 dosyscall32irqson arch/x86/entry/syscall32.c:83 [inline] ...
Affected Software
Remediation
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Ensure the device's attached status is checked before performing any ioctl, including compat ioctls, so ioctls cannot run on unconfigured devices.
Event History
Frequently Asked Questions
Which systems appear most likely to be affected?
The reported crashes appear to be exclusive to i386 kernels, based on the cited Syzbot reports. The issue is in compatibility versions of Comedi IOCTL handlers.
What condition is required to trigger the issue?
Selected Comedi IOCTLs must be invoked through compatibility handlers on a device that has not been properly configured or attached. This can occur even through COMEDI_DEVCONFIG, leaving callbacks such as dev->get_valid_routes() unset.
What is the observable impact?
The condition can cause a kernel crash through a null pointer dereference when an IOCTL reaches an expected device callback that was never initialized.