Re: [PATCH] Fix NULL ptr dereference in pci_bus_assign_domain_nr() on ARM

Bjorn Helgaas
2016-03-07T22:33:25Z

[+cc Lorenzo]

On Tue, Mar 01, 2016 at 07:07:18AM +0100, Krzysztof Hałasa wrote:
> Many ARM platforms use a wrapper:
> /*
> * Compatibility wrapper for older platforms that do not care about
> * passing the parent device.
> */
> static inline void pci_common_init(struct hw_pci *hw)
> {
> pci_common_init_dev(NULL, hw);
> }
>
> which means that pci_bus_assign_domain_nr() can be called without
> a parent. This patch fixes the NULL pointer dereference.
>
> Signed-off-by: Krzysztof Hałasa <khalasa@piap.pl>
> Cc: stable@vger.kernel.org

I applied this to for-linus with changelog as below for v4.5, thanks!

Wow, this is terrible. All ARM32 systems that use pci_common_init()
crash at boot. That includes cns3xxx, dove, footbridge, iopl13xx,
ip32x, iop33x, ixp4xx, ks8695, mv78xx0, orion5x, pxa, sa1100, etc.
Apparently they've been crashing since v4.0, when 7c674700098c and
8c7d14746abc appeared. I can hardly believe nobody noticed until now.

Actually, I did find one problem report:
http://forum.doozan.com/read.php?2,17868,22070,quote=1 from last May,
but apparently it got lost in a forum and never found its way
upstream.

I reworked the changelog because this problem will affect *any* arch
that enables CONFIG_PCI_DOMAINS_GENERIC and supplies NULL "parent"
pointers -- ia64, mips, mn10300, s390, x86, etc., would be affected if
they enabled CONFIG_PCI_DOMAINS_GENERIC.

I also added a "Fixes:" tag for 7c674700098c, since that's the commit
that added the generic code we're fixing. Backports of 7c674700098c
should also backport this change.

Bjorn

commit 71babd2a89fe
Author: Krzysztof =?utf-8?Q?Ha=C5=82asa?= <khalasa@piap.pl>
Date: Tue Mar 1 07:07:18 2016 +0100

PCI: Allow a NULL "parent" pointer in pci_bus_assign_domain_nr()

pci_create_root_bus() passes a "parent" pointer to
pci_bus_assign_domain_nr(). When CONFIG_PCI_DOMAINS_GENERIC is defined,
pci_bus_assign_domain_nr() dereferences that pointer. Many callers of
pci_create_root_bus() supply a NULL "parent" pointer, which leads to a NULL
pointer dereference error.

7c674700098c ("PCI: Move domain assignment from arm64 to generic code")
moved the "parent" dereference from arm64 to generic code. Only arm64 used
that code (because only arm64 defined CONFIG_PCI_DOMAINS_GENERIC), and it
always supplied a valid "parent" pointer. Other arches supplied NULL
"parent" pointers but didn't defined CONFIG_PCI_DOMAINS_GENERIC, so they
used a no-op version of pci_bus_assign_domain_nr().

8c7d14746abc ("ARM/PCI: Move to generic PCI domains") defined
CONFIG_PCI_DOMAINS_GENERIC on ARM, and many ARM platforms use
pci_common_init(), which supplies a NULL "parent" pointer.
These platforms (cns3xxx, dove, footbridge, iop13xx, etc.) crash
with a NULL pointer dereference like this while probing PCI:

Unable to handle kernel NULL pointer dereference at virtual address 000000a4
PC is at pci_bus_assign_domain_nr+0x10/0x84
LR is at pci_create_root_bus+0x48/0x2e4
Kernel panic - not syncing: Attempted to kill init!

[bhelgaas: changelog, add "Reported:" and "Fixes:" tags]
Reported: http://forum.doozan.com/read.php?2,17868,22070,quote=1
Fixes: 8c7d14746abc ("ARM/PCI: Move to generic PCI domains")
Fixes: 7c674700098c ("PCI: Move domain assignment from arm64 to generic code")
Signed-off-by: Krzysztof Hałasa <khalasa@piap.pl>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
CC: stable@vger.kernel.org # v4.0+

diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
index 602eb42..f89db3a 100644
--- a/drivers/pci/pci.c
+++ b/drivers/pci/pci.c
@@ -4772,8 +4772,10 @@ int pci_get_new_domain_nr(void)
void pci_bus_assign_domain_nr(struct pci_bus *bus, struct device *parent)
{
static int use_dt_domains = -1;
- int domain = of_get_pci_domain_nr(parent->of_node);
+ int domain = -1;

+ if (parent)
+ domain = of_get_pci_domain_nr(parent->of_node);
/*
* Check DT domain and use_dt_domains values.
*