mm: refuse wrapped vm_brk requests

The vm_brk() alignment calculations should refuse to overflow. The ELF
loader depending on this, but it has been fixed now. No other unsafe
callers have been found.

Link: http://lkml.kernel.org/r/[e-mail]
Signed-off-by: Kees Cook <[e-mail]>
Reported-by: Hector Marco-Gisbert <[e-mail]>
Cc: Ismael Ripoll Ripoll <[e-mail]>
Cc: Alexander Viro <[e-mail]>
Cc: "Kirill A. Shutemov" <[e-mail]>
Cc: Oleg Nesterov <[e-mail]>
Cc: Chen Gang <[e-mail]>
Cc: Michal Hocko <[e-mail]>
Cc: Konstantin Khlebnikov <[e-mail]>
Cc: Andrea Arcangeli <[e-mail]>
Cc: Andrey Ryabinin <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

mm/mmap.c

···
  *  anonymous maps.  eventually we may be able to do some
  *  brk-specific accounting here.
  */
-static int do_brk(unsigned long addr, unsigned long len)
+static int do_brk(unsigned long addr, unsigned long request)
 {
 	struct mm_struct *mm = current->mm;
 	struct vm_area_struct *vma, *prev;
-	unsigned long flags;
+	unsigned long flags, len;
 	struct rb_node **rb_link, *rb_parent;
 	pgoff_t pgoff = addr >> PAGE_SHIFT;
 	int error;
 
-	len = PAGE_ALIGN(len);
+	len = PAGE_ALIGN(request);
+	if (len < request)
+		return -ENOMEM;
 	if (!len)
 		return 0;