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

[Lorenzo Pieralisi]

On Mon, Mar 07, 2016 at 04:33:11PM -0600, Bjorn Helgaas wrote:
> [+cc Lorenzo]
> 
> On Tue, Mar 01, 2016 at 07:07:18AM +0100, Krzysztof Ha??asa 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 Ha??asa <khalasa at piap.pl>
> > Cc: stable at 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.

That's really unfortunate, when I moved code from arm64 to generic I
did not spot this issue in the original code and carried it over, you
summarized the reasons in the commit log so without any further ado (and
with my apologies):

Acked-by: Lorenzo Pieralisi <lorenzo.pieralisi at arm.com>

> 
> Bjorn
> 
> 
> 
> commit 71babd2a89fe
> Author: Krzysztof =?utf-8?Q?Ha=C5=82asa?= <khalasa at 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 Ha??asa <khalasa at piap.pl>
>     Signed-off-by: Bjorn Helgaas <bhelgaas at google.com>
>     CC: stable at 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.
>  	 *
>