PCI/AER: Restore pci_ops pointer while calling original pci_ops

The aer_inject module intercepts config space accesses by replacing the
bus->ops pointer.  If it forwards accesses to the original pci_ops, and
those original ops use bus->ops, they see the aer_pci_ops instead of their
own pci_ops, which can cause a crash.

For example, pci_generic_config_read() uses the bus->ops->map_bus pointer.
If bus->ops is set to aer_pci_ops, which doesn't supply .map_bus,
pci_generic_config_read() will dereference an invalid pointer and cause a
crash.

Temporarily restore the original bus->ops pointer while calling ops->read()
or ops->write().  Callers of these functions already hold pci_lock, which
prevents other users of bus->ops until we're finished.

[bhelgaas: changelog]
Signed-off-by: David Daney <david.daney@cavium.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>

drivers/pci/pcie/aer/aer_inject.c

@@ -188,7 +188,9 @@ static int aer_inj_read_config(struct pci_bus *bus, unsigned int devfn,
 	struct aer_error *err;
 	unsigned long flags;
 	struct pci_ops *ops;
+	struct pci_ops *my_ops;
 	int domain;
+	int rv;
 
 	spin_lock_irqsave(&inject_lock, flags);
 	if (size != sizeof(u32))
@@ -208,8 +210,19 @@ static int aer_inj_read_config(struct pci_bus *bus, unsigned int devfn,
 	}
 out:
 	ops = __find_pci_bus_ops(bus);
+	/*
+	 * pci_lock must already be held, so we can directly
+	 * manipulate bus->ops.  Many config access functions,
+	 * including pci_generic_config_read() require the original
+	 * bus->ops be installed to function, so temporarily put them
+	 * back.
+	 */
+	my_ops = bus->ops;
+	bus->ops = ops;
+	rv = ops->read(bus, devfn, where, size, val);
+	bus->ops = my_ops;
 	spin_unlock_irqrestore(&inject_lock, flags);
-	return ops->read(bus, devfn, where, size, val);
+	return rv;
 }
 
 static int aer_inj_write_config(struct pci_bus *bus, unsigned int devfn,
@@ -220,7 +233,9 @@ static int aer_inj_write_config(struct pci_bus *bus, unsigned int devfn,
 	unsigned long flags;
 	int rw1cs;
 	struct pci_ops *ops;
+	struct pci_ops *my_ops;
 	int domain;
+	int rv;
 
 	spin_lock_irqsave(&inject_lock, flags);
 	if (size != sizeof(u32))
@@ -243,8 +258,19 @@ static int aer_inj_write_config(struct pci_bus *bus, unsigned int devfn,
 	}
 out:
 	ops = __find_pci_bus_ops(bus);
+	/*
+	 * pci_lock must already be held, so we can directly
+	 * manipulate bus->ops.  Many config access functions,
+	 * including pci_generic_config_write() require the original
+	 * bus->ops be installed to function, so temporarily put them
+	 * back.
+	 */
+	my_ops = bus->ops;
+	bus->ops = ops;
+	rv = ops->write(bus, devfn, where, size, val);
+	bus->ops = my_ops;
 	spin_unlock_irqrestore(&inject_lock, flags);
-	return ops->write(bus, devfn, where, size, val);
+	return rv;
 }
 
 static struct pci_ops aer_inj_pci_ops = {