Re: [PATCH] misc: hpilo: Fix use after free bug in ilo_remove due to race condition with ilo_open

[Dan Carpenter]

On Fri, May 05, 2023 at 12:01:17PM +0800, Zheng Hacker wrote:
> Dear Dan,
> 
> Thanks for your reply. I'm not so familiar with the code here. Is the
> warning says we should check ilo_hw to see if it's not NULL?
> 

Just delete the NULL check.  It's impossible.

regards,
dan carpenter

> Best regards,
> Zheng
> 
> Dan Carpenter <dan.carpenter@xxxxxxxxxx> 于2023年5月2日周二 19:46写道：
> >
> > Hi Zheng,
> >
> > kernel test robot noticed the following build warnings:
> >
> > https://git-scm.com/docs/git-format-patch#_base_tree_information]
> >
> > url:    https://github.com/intel-lab-lkp/linux/commits/Zheng-Wang/misc-hpilo-Fix-use-after-free-bug-in-ilo_remove-due-to-race-condition-with-ilo_open/20230418-005502
> > base:   char-misc/char-misc-testing
> > patch link:    https://lore.kernel.org/r/20230417165246.467723-1-zyytlz.wz%40163.com
> > patch subject: [PATCH] misc: hpilo: Fix use after free bug in ilo_remove due  to race condition with ilo_open
> > config: i386-randconfig-m021 (https://download.01.org/0day-ci/archive/20230430/202304300909.ALHN6Vry-lkp@xxxxxxxxx/config)
> > compiler: gcc-11 (Debian 11.3.0-12) 11.3.0
> >
> > If you fix the issue, kindly add following tag where applicable
> > | Reported-by: kernel test robot <lkp@xxxxxxxxx>
> > | Reported-by: Dan Carpenter <error27@xxxxxxxxx>
> > | Link: https://lore.kernel.org/r/202304300909.ALHN6Vry-lkp@xxxxxxxxx/
> >
> > smatch warnings:
> > drivers/misc/hpilo.c:755 ilo_delete() warn: can 'ilo_hw' even be NULL?
> >
> > vim +/ilo_hw +755 drivers/misc/hpilo.c
> >
> > 13a22f45e6cb1e Zheng Wang      2023-04-18  749  static void ilo_delete(struct kref *kref)
> > 13a22f45e6cb1e Zheng Wang      2023-04-18  750  {
> > 13a22f45e6cb1e Zheng Wang      2023-04-18  751          int i, minor;
> > 13a22f45e6cb1e Zheng Wang      2023-04-18  752          struct ilo_hwinfo *ilo_hw = container_of(kref, struct ilo_hwinfo, refcnt);
> > 13a22f45e6cb1e Zheng Wang      2023-04-18  753          struct pci_dev *pdev = ilo_hw->ilo_dev;
> > 89bcb05d9bbf8b David Altobelli 2008-07-02  754
> > ebf1b764aa5cb3 Mark Rusk       2012-11-06 @755          if (!ilo_hw)
> >                                                             ^^^^^^^
> >
> > ->refcnt member isn't the first struct member so this NULL check
> > doesn't make sense.  Generally checking container_of() is ugly.  Some
> > people do it and add BUILD_BUG_ON() to ensure that they're checking the
> > first struct member but really it's best to avoid that if possible.
> >
> > ebf1b764aa5cb3 Mark Rusk       2012-11-06  756                  return;
> > ebf1b764aa5cb3 Mark Rusk       2012-11-06  757
> > 89bcb05d9bbf8b David Altobelli 2008-07-02  758          clear_device(ilo_hw);
> > 89bcb05d9bbf8b David Altobelli 2008-07-02  759
> > 89bcb05d9bbf8b David Altobelli 2008-07-02  760          minor = MINOR(ilo_hw->cdev.dev);
> > 98dcd59dd063dd Camuso, Tony    2012-06-10  761          for (i = minor; i < minor + max_ccb; i++)
> > 89bcb05d9bbf8b David Altobelli 2008-07-02  762                  device_destroy(ilo_class, MKDEV(ilo_major, i));
> > 89bcb05d9bbf8b David Altobelli 2008-07-02  763
> > 89bcb05d9bbf8b David Altobelli 2008-07-02  764          cdev_del(&ilo_hw->cdev);
> > 9f7048412163d8 David Altobelli 2009-08-17  765          ilo_disable_interrupts(ilo_hw);
> > 9f7048412163d8 David Altobelli 2009-08-17  766          free_irq(pdev->irq, ilo_hw);
> > 89bcb05d9bbf8b David Altobelli 2008-07-02  767          ilo_unmap_device(pdev, ilo_hw);
> > 89bcb05d9bbf8b David Altobelli 2008-07-02  768          pci_release_regions(pdev);
> > bcdee04ea7ae04 Jiri Slaby      2012-09-13  769          /*
> > bcdee04ea7ae04 Jiri Slaby      2012-09-13  770           * pci_disable_device(pdev) used to be here. But this PCI device has
> > bcdee04ea7ae04 Jiri Slaby      2012-09-13  771           * two functions with interrupt lines connected to a single pin. The
> > bcdee04ea7ae04 Jiri Slaby      2012-09-13  772           * other one is a USB host controller. So when we disable the PIN here
> > bcdee04ea7ae04 Jiri Slaby      2012-09-13  773           * e.g. by rmmod hpilo, the controller stops working. It is because
> > bcdee04ea7ae04 Jiri Slaby      2012-09-13  774           * the interrupt link is disabled in ACPI since it is not refcounted
> > bcdee04ea7ae04 Jiri Slaby      2012-09-13  775           * yet. See acpi_pci_link_free_irq called from acpi_pci_irq_disable.
> > bcdee04ea7ae04 Jiri Slaby      2012-09-13  776           */
> > 89bcb05d9bbf8b David Altobelli 2008-07-02  777          kfree(ilo_hw);
> > 98dcd59dd063dd Camuso, Tony    2012-06-10  778          ilo_hwdev[(minor / max_ccb)] = 0;
> > 89bcb05d9bbf8b David Altobelli 2008-07-02  779  }
> >
> > --
> > 0-DAY CI Kernel Test Service
> > https://github.com/intel/lkp-tests
> >