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

mm/mmap.c

@@ -2653,16 +2653,18 @@ static inline void verify_mm_writelocked(struct mm_struct *mm)
  *  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;