[PATCH] USB: EHCI: fix NULL pointer dererence in HCDs that use HCD_LOCAL_MEM

[Andrea Righi <arighi@develer.com>]

If we use the HCD_LOCAL_MEM flag and dma_declare_coherent_memory() to
enforce the host controller's local memory utilization we also need to
disable native scatter-gather support, otherwise hcd_alloc_coherent() in
map_urb_for_dma() is called with urb->transfer_buffer == NULL, that
triggers a NULL pointer dereference.

We can also consider to add a WARN_ON() and return an error code to
better catch this problem in the future.

Signed-off-by: Andrea Righi <arighi@develer.com>
---
 drivers/usb/core/hcd.c      |    5 +++++
 drivers/usb/host/ehci-hcd.c |    3 ++-
 2 files changed, 7 insertions(+), 1 deletions(-)

diff --git a/drivers/usb/core/hcd.c b/drivers/usb/core/hcd.c
index 12742f1..161c757 100644
--- a/drivers/usb/core/hcd.c
+++ b/drivers/usb/core/hcd.c
@@ -1219,6 +1219,11 @@ static int hcd_alloc_coherent(struct usb_bus *bus,
 {
 	unsigned char *vaddr;
 
+	if (*vaddr_handle == NULL) {
+		WARN_ON_ONCE(1);
+		return -EFAULT;
+	}
+
 	vaddr = hcd_buffer_alloc(bus, size + sizeof(vaddr),
 				 mem_flags, dma_handle);
 	if (!vaddr)
diff --git a/drivers/usb/host/ehci-hcd.c b/drivers/usb/host/ehci-hcd.c
index a3ef2a9..27e0351 100644
--- a/drivers/usb/host/ehci-hcd.c
+++ b/drivers/usb/host/ehci-hcd.c
@@ -606,7 +606,8 @@ static int ehci_init(struct usb_hcd *hcd)
 	ehci->command = temp;
 
 	/* Accept arbitrarily long scatter-gather lists */
-	hcd->self.sg_tablesize = ~0;
+	if (!(hcd->driver->flags & HCD_LOCAL_MEM))
+		hcd->self.sg_tablesize = ~0;
 	return 0;
 }