mm: fix overflow in vm_map_ram()

When remapping pages accounting for 4G or more memory space, the
operation 'count << PAGE_SHIFT' overflows as it is performed on an
integer. Solution: cast before doing the bitshift.

[[e-mail]: fix vm_unmap_ram() also]
[[e-mail]: fix vmap() as well, per Guillermo]
Link: http://lkml.kernel.org/r/[e-mail]
Signed-off-by: Guillermo Julián Moreno <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

mm/vmalloc.c

···
  */
 void vm_unmap_ram(const void *mem, unsigned int count)
 {
-	unsigned long size = count << PAGE_SHIFT;
+	unsigned long size = (unsigned long)count << PAGE_SHIFT;
 	unsigned long addr = (unsigned long)mem;
 
 	BUG_ON(!addr);
···
  */
 void *vm_map_ram(struct page **pages, unsigned int count, int node, pgprot_t prot)
 {
-	unsigned long size = count << PAGE_SHIFT;
+	unsigned long size = (unsigned long)count << PAGE_SHIFT;
 	unsigned long addr;
 	void *mem;
 
···
 		unsigned long flags, pgprot_t prot)
 {
 	struct vm_struct *area;
+	unsigned long size;		/* In bytes */
 
 	might_sleep();
 
 	if (count > totalram_pages)
 		return NULL;
 
-	area = get_vm_area_caller((count << PAGE_SHIFT), flags,
-					__builtin_return_address(0));
+	size = (unsigned long)count << PAGE_SHIFT;
+	area = get_vm_area_caller(size, flags, __builtin_return_address(0));
 	if (!area)
 		return NULL;