UIO: Fix mapping of logical and virtual memory

mmap() doesn't work as expected for UIO_MEM_LOGICAL or UIO_MEM_VIRTUAL
mappings. The offset into the memory needs to be added, otherwise
uio_vma_fault always returns the first page only. Note that for UIO
userspace calls mmap() with offset = N * getpagesize() to access
mapping N. This must be compensated when calculating the offset. A
comment was added to explain this since it is not obvious.

Signed-off-by: Andrew G. Harvey <[email protected]>
Signed-off-by: Hans J. Koch <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>

drivers/uio/uio.c

@@ -490,15 +490,23 @@ static int uio_vma_fault(struct vm_area_struct *vma, struct vm_fault *vmf)
 {
 	struct uio_device *idev = vma->vm_private_data;
 	struct page *page;
+	unsigned long offset;
 
 	int mi = uio_find_mem_index(vma);
 	if (mi < 0)
 		return VM_FAULT_SIGBUS;
 
+	/*
+	 * We need to subtract mi because userspace uses offset = N*PAGE_SIZE
+	 * to use mem[N].
+	 */
+	offset = (vmf->pgoff - mi) << PAGE_SHIFT;
+
 	if (idev->info->mem[mi].memtype == UIO_MEM_LOGICAL)
-		page = virt_to_page(idev->info->mem[mi].addr);
+		page = virt_to_page(idev->info->mem[mi].addr + offset);
 	else
-		page = vmalloc_to_page((void*)idev->info->mem[mi].addr);
+		page = vmalloc_to_page((void *)idev->info->mem[mi].addr
+							+ offset);
 	get_page(page);
 	vmf->page = page;
 	return 0;