[PATCH] USB: EHCI: fix conflation of buf == 0 with len == 0

When the ehci-hcd driver prepares a control URB, it tests for a
zero-length data stage by looking at the transfer_dma value instead of
the transfer_buffer_length.  (In fact it does this even for non-control
URBs, which is an additional aspect of the same bug.)

However, under certain circumstances it's possible for transfer_dma to
be 0 while transfer_buffer_length is non-zero.  This can happen when a
freshly allocated page (mapped to address 0 and marked Copy-On-Write,
but never written to) is used as the source buffer for an OUT transfer.
This patch (as598) fixes the problem.

Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

1 files changed, 7 insertions, 7 deletions

diff --git a/drivers/usb/host/ehci-q.c b/drivers/usb/host/ehci-q.c
index bf03ec0d8ee2..9b13bf2fa98d 100644
--- a/drivers/usb/host/ehci-q.c
+++ b/drivers/usb/host/ehci-q.c
@@ -514,18 +514,18 @@ qh_urb_transaction (
                 qtd->urb = urb;
                 qtd_prev->hw_next = QTD_NEXT (qtd->qtd_dma);
                 list_add_tail (&qtd->qtd_list, head);
+
+                /* for zero length DATA stages, STATUS is always IN */
+                if (len == 0)
+                        token |= (1 /* "in" */ << 8);
         } 
 
         /*
          * data transfer stage:  buffer setup
          */
-        if (likely (len > 0))
-                buf = urb->transfer_dma;
-        else
-                buf = 0;
+        buf = urb->transfer_dma;
 
-        /* for zero length DATA stages, STATUS is always IN */
-        if (!buf || is_input)
+        if (is_input)
                 token |= (1 /* "in" */ << 8);
         /* else it's already initted to "out" pid (0 << 8) */
 
@@ -572,7 +572,7 @@ qh_urb_transaction (
          * control requests may need a terminating data "status" ack;
          * bulk ones may need a terminating short packet (zero length).
          */
-        if (likely (buf != 0)) {
+        if (likely (urb->transfer_buffer_length != 0)) {
                 int     one_more = 0;
 
                 if (usb_pipecontrol (urb->pipe)) {