Description

In the Linux kernel, the following vulnerability has been resolved: comedi: pcl818: fix null-ptr-deref in pcl818_ai_cancel() Syzbot identified an issue [1] in pcl818_ai_cancel(), which stems from the fact that in case of early device detach via pcl818_detach(), subdevice dev->read_subdev may not have initialized its pointer to &struct comedi_async as intended. Thus, any such dereferencing of &s->async->cmd will lead to general protection fault and kernel crash. Mitigate this problem by removing a call to pcl818_ai_cancel() from pcl818_detach() altogether. This way, if the subdevice setups its support for async commands, everything async-related will be handled via subdevice's own ->cancel() function in comedi_device_detach_locked() even before pcl818_detach(). If no support for asynchronous commands is provided, there is no need to cancel anything either. [1] Syzbot crash: Oops: general protection fault, probably for non-canonical address 0xdffffc0000000005: 0000 [#1] SMP KASAN PTI KASAN: null-ptr-deref in range [0x0000000000000028-0x000000000000002f] CPU: 1 UID: 0 PID: 6050 Comm: syz.0.18 Not tainted syzkaller #0 PREEMPT(full) Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/18/2025 RIP: 0010:pcl818_ai_cancel+0x69/0x3f0 drivers/comedi/drivers/pcl818.c:762 ... Call Trace: <TASK> pcl818_detach+0x66/0xd0 drivers/comedi/drivers/pcl818.c:1115 comedi_device_detach_locked+0x178/0x750 drivers/comedi/drivers.c:207 do_devconfig_ioctl drivers/comedi/comedi_fops.c:848 [inline] comedi_unlocked_ioctl+0xcde/0x1020 drivers/comedi/comedi_fops.c:2178 vfs_ioctl fs/ioctl.c:51 [inline] __do_sys_ioctl fs/ioctl.c:597 [inline] ...

References 7

• git.kernel.org https://git.kernel.org/stable/c/5caa40e7c6a43e08e3574f990865127705c22861
• git.kernel.org https://git.kernel.org/stable/c/877adccfacb32687b90714a27cfb09f444fdfa16
• git.kernel.org https://git.kernel.org/stable/c/88d99ca5adbd01ff088f5fb2ddeba5755e085e52
• git.kernel.org https://git.kernel.org/stable/c/935ad4b3c325c24fff2c702da403283025ffc722
• git.kernel.org https://git.kernel.org/stable/c/a51f025b5038abd3d22eed2ede4cd46793d89565
• git.kernel.org https://git.kernel.org/stable/c/b2a5b172dc05be6c4f2c5542c1bbc6b14d60ff16
• git.kernel.org https://git.kernel.org/stable/c/d948c53dec36dafe182631457597c49c1f1df5ea

Remediation