[4.2.y-ckt stable] Patch "PCI: Allow a NULL "parent" pointer in pci_bus_assign_domain_nr()" has been added to the 4.2.y-ckt tree

[Kamal Mostafa]

This is a note to let you know that I have just added a patch titled

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

to the linux-4.2.y-queue branch of the 4.2.y-ckt extended stable tree 
which can be found at:

    http://kernel.ubuntu.com/git/ubuntu/linux.git/log/?h=linux-4.2.y-queue

This patch is scheduled to be released in version 4.2.8-ckt6.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 4.2.y-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Kamal

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 <khalasa at piap.pl>
Date: Tue, 1 Mar 2016 07:07:18 +0100
Subject: PCI: Allow a NULL "parent" pointer in pci_bus_assign_domain_nr()
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commit 54c6e2dd00c313d0add58e5befe62fe6f286d03b upstream.

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 at piap.pl>
Signed-off-by: Bjorn Helgaas <bhelgaas at google.com>
Acked-by: Lorenzo Pieralisi <lorenzo.pieralisi at arm.com>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 drivers/pci/pci.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
index 0008c95..f6f2384 100644
--- a/drivers/pci/pci.c
+++ b/drivers/pci/pci.c
@@ -4487,8 +4487,10 @@ 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.
 	 *
--
2.7.0