On 12/3/20 11:27 AM, Dan Carpenter wrote:
> tree: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
> master
> head: 3bb61aa61828499a7d0f5e560051625fd02ae7e4
> commit: 3047766bc6ec9c6bc9ece85b45a41ff401e8d988 s390/pci: fix enabling a
> reserved PCI function
>
> If you fix the issue, kindly add following tag as appropriate
> Reported-by: kernel test robot <l...@intel.com>
> Reported-by: Dan Carpenter <dan.carpen...@oracle.com>
>
> smatch warnings:
> arch/s390/pci/pci_event.c:101 __zpci_event_availability() error: we
> previously assumed 'zdev->zbus' could be null (see line 83)
>
> vim +101 arch/s390/pci/pci_event.c
>
> aa3b7c296732b43 Sebastian Ott 2013-12-12 76 static void
> __zpci_event_availability(struct zpci_ccdf_avail *ccdf)
> cbc0dd1f856b52b Jan Glauber 2012-11-29 77 {
> cbc0dd1f856b52b Jan Glauber 2012-11-29 78 struct zpci_dev *zdev =
> get_zdev_by_fid(ccdf->fid);
> 9a99649f2a89fdf Sebastian Ott 2016-01-29 79 struct pci_dev *pdev =
> NULL;
> 623bd44d3f277b7 Sebastian Ott 2017-05-09 80 enum zpci_state state;
> d795ddad36cbc82 Sebastian Ott 2013-11-15 81 int ret;
> cbc0dd1f856b52b Jan Glauber 2012-11-29 82
> 05bc1be6db4b268 Pierre Morel 2020-03-23 @83 if (zdev && zdev->zbus
> && zdev->zbus->bus)
> ^^^^^^^^^
> Check for NULL
>
> 44510d6fa0c00aa Pierre Morel 2020-04-22 84 pdev =
> pci_get_slot(zdev->zbus->bus, zdev->devfn);
> 9a99649f2a89fdf Sebastian Ott 2016-01-29 85
> 1f1dcbd4f23bd1f Sebastian Ott 2013-10-22 86 zpci_err("avail
> CCDF:\n");
> 1f1dcbd4f23bd1f Sebastian Ott 2013-10-22 87 zpci_err_hex(ccdf,
> sizeof(*ccdf));
> cbc0dd1f856b52b Jan Glauber 2012-11-29 88
> cbc0dd1f856b52b Jan Glauber 2012-11-29 89 switch (ccdf->pec) {
> 7fc611ff3ff1a0b Sebastian Ott 2015-06-16 90 case 0x0301: /*
> Reserved|Standby -> Configured */
> 7fc611ff3ff1a0b Sebastian Ott 2015-06-16 91 if (!zdev) {
> f606b3ef47c9f87 Pierre Morel 2020-03-25 92 ret =
> clp_add_pci_device(ccdf->fid, ccdf->fh, 1);
> 7fc611ff3ff1a0b Sebastian Ott 2015-06-16 93 break;
> 7fc611ff3ff1a0b Sebastian Ott 2015-06-16 94 }
> fcf2f402937a669 Sebastian Ott 2013-12-18 95 zdev->fh =
> ccdf->fh;
> f606b3ef47c9f87 Pierre Morel 2020-03-25 96 zdev->state =
> ZPCI_FN_STATE_CONFIGURED;
> 3047766bc6ec9c6 Niklas Schnelle 2020-06-18 97 ret =
> zpci_enable_device(zdev);
> 3047766bc6ec9c6 Niklas Schnelle 2020-06-18 98 if (ret)
> 3047766bc6ec9c6 Niklas Schnelle 2020-06-18 99 break;
> 3047766bc6ec9c6 Niklas Schnelle 2020-06-18 100
> 3047766bc6ec9c6 Niklas Schnelle 2020-06-18 @101 pdev =
> pci_scan_single_device(zdev->zbus->bus, zdev->devfn);
>
> ^^^^^^^^^^^^^^^^
> Unchecked dereference
First, thanks for reporting this is definitely appreciated!
We have also seen the same smatch report internally
and I determined that this is a false positive.
This is because the existing zdev->zbus NULL check could already never
trigger. Sadly this is all a bit hard to see but let me try to share
my reasoning here. That said, we do plan a couple of cleanups/rework here
that will also see the removal of the zdev->zbus NULL check at the start
of the function.
The existing check is here:
76 static void __zpci_event_availability(struct zpci_ccdf_avail *ccdf)
77 {
78 struct zpci_dev *zdev = get_zdev_by_fid(ccdf->fid);
79 struct pci_dev *pdev = NULL;
80 enum zpci_state state;
81 int ret;
82
83 if (zdev && zdev->zbus && zdev->zbus->bus)
84 pdev = pci_get_slot(zdev->zbus->bus, zdev->devfn);
Now for both the new zdev->zbus->bus dereference and the check in line 83 we
check zdev != NULL beforehand. So that's a given.
If we have the zdev it came out of get_zdev_by_fid() (line 78) which found it in
the zpci_list.
It only ever gets into that list in zpci_create_device() and
gets removed if anything in there fails, including zpci_bus_register_device()
which when successful has definitely set zdev->zbus != NULL.
Furthermore zpci_create_device() is only called in clp_add_pci_device()
which is either called during init of zPCI (in the initial CLP List PCI)
or from the kthread that handles events via zpci_event_availability()
which checks the the initialization is complete.
Therefore there is no race for the window in which
zpci_create_device() has the zdev in the list but no zbus set.
Either way, this is definitely too hard to reason about e.g.
we should only add devices to the zpci_list once they are
fully initialized and we're working on a redesign of this.
If you prefer a short term fix so this doesn't trigger
again we could simply remove the zdev->zbus NULL check.
>
... snip ...
