From: Nikita Zhandarovich Date: Thu, 23 Oct 2025 14:14:56 +0000 (+0300) Subject: comedi: pcl818: fix null-ptr-deref in pcl818_ai_cancel() X-Git-Tag: v6.17.12~53 X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=d948c53dec36dafe182631457597c49c1f1df5ea;p=thirdparty%2Fkernel%2Fstable.git comedi: pcl818: fix null-ptr-deref in pcl818_ai_cancel() commit a51f025b5038abd3d22eed2ede4cd46793d89565 upstream. 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: 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] ... Reported-by: syzbot+fce5d9d5bd067d6fbe9b@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=fce5d9d5bd067d6fbe9b Fixes: 00aba6e7b565 ("staging: comedi: pcl818: remove 'neverending_ai' from private data") Cc: stable Signed-off-by: Nikita Zhandarovich Reviewed-by: Ian Abbott Link: https://patch.msgid.link/20251023141457.398685-1-n.zhandarovich@fintech.ru Signed-off-by: Greg Kroah-Hartman Signed-off-by: Greg Kroah-Hartman --- diff --git a/drivers/comedi/drivers/pcl818.c b/drivers/comedi/drivers/pcl818.c index 4127adcfb2295..06fe06396f23a 100644 --- a/drivers/comedi/drivers/pcl818.c +++ b/drivers/comedi/drivers/pcl818.c @@ -1111,10 +1111,9 @@ static void pcl818_detach(struct comedi_device *dev) { struct pcl818_private *devpriv = dev->private; - if (devpriv) { - pcl818_ai_cancel(dev, dev->read_subdev); + if (devpriv) pcl818_reset(dev); - } + pcl818_free_dma(dev); comedi_legacy_detach(dev); }