From 17221216ae8ce6a24e8a4e787382e3ebc81b88a8 Mon Sep 17 00:00:00 2001 From: Ian Abbott Date: Wed, 27 May 2026 13:51:03 +0100 Subject: [PATCH] comedi: comedi_parport: deal with premature interrupt Syzbot reported a general protection fault in `comedi_get_is_subdevice_running()`, which was called from the interrupt handler `parport_interrupt()` in the "comedi_parport" driver, but it does not currently have a C reproducer for the problem. It's probably due to a premature interrupt for one of two reasons: 1. The driver sets up the interrupt handler before the comedi subdevices used by the interrupt handler have been allocated, but does not disable the interrupt in the parallel port's CTRL register first. 2. The driver uses a user-supplied I/O port base address which Syzbot would have supplied, but it might not be backed by real parallel port hardware. Change the initialization order in the driver's comedi "attach" handler (`parport_attach()`) so that the hardware registers are initialized before the interrupt handler is requested. This should prevent premature interrupts occurring for real hardware. Also add a test to the interrupt handler to ensure the comedi device is fully attached and return early if it isn't. Fixes: 241ab6ad7108e ("Staging: comedi: add comedi_parport driver") Reported-by: syzbot+f24c3d5d316011bacc70@syzkaller.appspotmail.com Cc: stable Signed-off-by: Ian Abbott Link: https://patch.msgid.link/20260527125104.96596-1-abbotti@mev.co.uk Signed-off-by: Greg Kroah-Hartman --- drivers/comedi/drivers/comedi_parport.c | 13 ++++++++++--- 1 file changed, 10 insertions(+), 3 deletions(-) diff --git a/drivers/comedi/drivers/comedi_parport.c b/drivers/comedi/drivers/comedi_parport.c index 2604680d86c4..57ee3f9dfba2 100644 --- a/drivers/comedi/drivers/comedi_parport.c +++ b/drivers/comedi/drivers/comedi_parport.c @@ -211,6 +211,13 @@ static irqreturn_t parport_interrupt(int irq, void *d) unsigned int ctrl; unsigned short val = 0; + /* + * Check device is fully attached. Device interrupts should have + * been disabled, but do this in case of bad hardware. + */ + if (!dev->attached) + return IRQ_NONE; + ctrl = inb(dev->iobase + PARPORT_CTRL_REG); if (!(ctrl & PARPORT_CTRL_IRQ_ENA)) return IRQ_NONE; @@ -233,6 +240,9 @@ static int parport_attach(struct comedi_device *dev, if (ret) return ret; + outb(0, dev->iobase + PARPORT_DATA_REG); + outb(0, dev->iobase + PARPORT_CTRL_REG); + if (it->options[1]) { ret = request_irq(it->options[1], parport_interrupt, 0, dev->board_name, dev); @@ -288,9 +298,6 @@ static int parport_attach(struct comedi_device *dev, s->cancel = parport_intr_cancel; } - outb(0, dev->iobase + PARPORT_DATA_REG); - outb(0, dev->iobase + PARPORT_CTRL_REG); - return 0; }