[PATCH 2/2] mm: refuse wrapped vm_brk requests

[Kees Cook <keescook@chromium.org>]

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.

Reported-by: Hector Marco-Gisbert <hecmargi@upv.es>
Signed-off-by: Kees Cook <keescook@chromium.org>
---
 mm/mmap.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/mm/mmap.c b/mm/mmap.c
index de2c1769cc68..1874ee0e1266 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -2625,16 +2625,18 @@ 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;
 
-- 
2.7.4