usb; xhci: Fix TRB offset calculations.

Greg KH introduced a bug into xhci_trb_virt_to_dma() when he changed the
type of offset to dma_addr_t from unsigned int and dropped the casts to
unsigned int around the virtual address pointer subtraction.

trb and seg->trbs are both valid pointers to virtual addresses, so the
compiler will mod the subtraction by the size of union trb (16 bytes).
segment_offset is an unsigned long, which is guaranteed to be at least as
big as a void *.

Drop the void * casts in the first if statement because trb and seg->trbs
are both pointers of the same type (pointers to union trb).

Signed-off-by: Sarah Sharp <sarah.a.sharp@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

1 files changed, 6 insertions, 7 deletions

diff --git a/drivers/usb/host/xhci-ring.c b/drivers/usb/host/xhci-ring.c
index d42a738cdaa7..02d81985c454 100644
--- a/drivers/usb/host/xhci-ring.c
+++ b/drivers/usb/host/xhci-ring.c
@@ -74,16 +74,15 @@
 dma_addr_t xhci_trb_virt_to_dma(struct xhci_segment *seg,
                 union xhci_trb *trb)
 {
-        dma_addr_t offset;
+        unsigned long segment_offset;
 
-        if (!seg || !trb || (void *) trb < (void *) seg->trbs)
+        if (!seg || !trb || trb < seg->trbs)
                 return 0;
-        /* offset in bytes, since these are byte-addressable */
-        offset = trb - seg->trbs;
-        /* SEGMENT_SIZE in bytes, trbs are 16-byte aligned */
-        if (offset > SEGMENT_SIZE || (offset % sizeof(*trb)) != 0)
+        /* offset in TRBs */
+        segment_offset = trb - seg->trbs;
+        if (segment_offset > TRBS_PER_SEGMENT)
                 return 0;
-        return seg->dma + offset;
+        return seg->dma + (segment_offset * sizeof(*trb));
 }
 
 /* Does this link TRB point to the first segment in a ring,