[PATCH 2.6.32.stable] ACPI: Add NULL pointer check in acpi_bus_start

[Len Brown <lenb@kernel.org>]

upstream d2f6650a950dadd20667a04a9dc785f240d43695
From: Thomas Renninger <trenn@suse.de>

If acpi_bus_add does not return a device and it's passed
to acpi_bus_start, bad things will happen:

BUG: unable to handle kernel NULL pointer dereference at 0000000000000008
IP: [<ffffffff8128402d>] acpi_bus_start+0x14/0x24
...
[<ffffffffa008977a>] acpiphp_bus_add+0xba/0x130 [acpiphp]
[<ffffffffa008aa72>] enable_device+0x132/0x2ff [acpiphp]
[<ffffffffa0089b68>] acpiphp_enable_slot+0xb8/0x130 [acpiphp]
[<ffffffffa0089df7>] handle_hotplug_event_func+0x87/0x190 [acpiphp]

Next patch would make this NULL pointer check obsolete, but
better having one more than one missing...

Signed-off-by: Thomas Renninger <trenn@suse.de>
Acked-by: Bjorn Helgaas <bjorn.helgaas@hp.com>
CC: stable@kernel.org
Signed-off-by: Len Brown <len.brown@intel.com>
---
 drivers/acpi/scan.c |    3 +++
 1 files changed, 3 insertions(+), 0 deletions(-)

diff --git a/drivers/acpi/scan.c b/drivers/acpi/scan.c
index ff9f622..8044583 100644
--- a/drivers/acpi/scan.c
+++ b/drivers/acpi/scan.c
@@ -1357,6 +1357,9 @@ int acpi_bus_start(struct acpi_device *device)
 {
 	struct acpi_bus_ops ops;
 
+	if (!device)
+		return -EINVAL;
+
 	memset(&ops, 0, sizeof(ops));
 	ops.acpi_op_start = 1;
 
-- 
1.7.0.17.g7e5eb