6.6-stable review patch. If anyone has any objections, please let me know.
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From: Nikita Zhandarovich n.zhandarovich@fintech.ru
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: <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] ...
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 stable@kernel.org Signed-off-by: Nikita Zhandarovich n.zhandarovich@fintech.ru Reviewed-by: Ian Abbott abbotti@mev.co.uk Link: https://patch.msgid.link/20251023141457.398685-1-n.zhandarovich@fintech.ru Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- drivers/comedi/drivers/pcl818.c | 5 ++--- 1 file changed, 2 insertions(+), 3 deletions(-)
--- a/drivers/comedi/drivers/pcl818.c +++ b/drivers/comedi/drivers/pcl818.c @@ -1111,10 +1111,9 @@ static void pcl818_detach(struct comedi_ { 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); }