PCI: aer_inject: Don't call config read/write functions with invalid ops structure.

From: David Daney <david.daney@cavium.com>

The aer_inject module, when active, replaces the pci_ops structure of
the bus so that it can intercept config space accesses.  If the config
space access needs to be forwarded to the original pci_ops, we must
restore the bus's original ops, as the read()/write() functions may
require use of the data in the pci_ops structure.  An example of such
functions are the pci_generic_config*() functions in
drivers/pci/access.c.  A failure to call these with a valid bus->ops
results in dereferencing an invalid bus->ops->map_bus pointer and
subsequent OOPs and system crash.

So, do as suggested above.  When calling to the original
read()/write() functions, temporarily switch back to the original
pci_ops.  This is safe to do as the pci_lock must already be held, and
thus no other users of the bus->ops are possible.

Signed-off-by: David Daney <david.daney@cavium.com>
---
 drivers/pci/pcie/aer/aer_inject.c | 30 ++++++++++++++++++++++++++++--
 1 file changed, 28 insertions(+), 2 deletions(-)

On Tue, Dec 22, 2015 at 01:44:51PM -0800, David Daney wrote:
> From: David Daney <david.daney@cavium.com>
> 
> The aer_inject module, when active, replaces the pci_ops structure of
> the bus so that it can intercept config space accesses.  If the config
> space access needs to be forwarded to the original pci_ops, we must
> restore the bus's original ops, as the read()/write() functions may
> require use of the data in the pci_ops structure.  An example of such
> functions are the pci_generic_config*() functions in
> drivers/pci/access.c.  A failure to call these with a valid bus->ops
> results in dereferencing an invalid bus->ops->map_bus pointer and
> subsequent OOPs and system crash.
> 
> So, do as suggested above.  When calling to the original
> read()/write() functions, temporarily switch back to the original
> pci_ops.  This is safe to do as the pci_lock must already be held, and
> thus no other users of the bus->ops are possible.
> 
> Signed-off-by: David Daney <david.daney@cavium.com>

Applied to pci/aer for v4.6, thanks, David!

> ---
>  drivers/pci/pcie/aer/aer_inject.c | 30 ++++++++++++++++++++++++++++--
>  1 file changed, 28 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/pci/pcie/aer/aer_inject.c b/drivers/pci/pcie/aer/aer_inject.c
> index 182224a..2d60e0e 100644
> --- a/drivers/pci/pcie/aer/aer_inject.c
> +++ b/drivers/pci/pcie/aer/aer_inject.c
> @@ -188,7 +188,9 @@ static int pci_read_aer(struct pci_bus *bus, unsigned int devfn, int where,
>  	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 pci_read_aer(struct pci_bus *bus, unsigned int devfn, int where,
>  	}
>  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 pci_write_aer(struct pci_bus *bus, unsigned int devfn, int where,
> @@ -220,7 +233,9 @@ static int pci_write_aer(struct pci_bus *bus, unsigned int devfn, int where,
>  	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 pci_write_aer(struct pci_bus *bus, unsigned int devfn, int where,
>  	}
>  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 pci_ops_aer = {
> -- 
> 1.8.3.1
> 
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