security: protect from stack expantion into low vm addresses

Add security checks to make sure we are not attempting to expand the
stack into memory protected by mmap_min_addr

Signed-off-by: Eric Paris <eparis@redhat.com>
Signed-off-by: James Morris <jmorris@namei.org>

1 files changed, 6 insertions, 2 deletions

diff --git a/mm/mmap.c b/mm/mmap.c
index facc1a75bd4f..938313c76d02 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -1615,6 +1615,12 @@ static inline int expand_downwards(struct vm_area_struct *vma,
          */
         if (unlikely(anon_vma_prepare(vma)))
                 return -ENOMEM;
+
+        address &= PAGE_MASK;
+        error = security_file_mmap(0, 0, 0, 0, address, 1);
+        if (error)
+                return error;
+
         anon_vma_lock(vma);
 
         /*
@@ -1622,8 +1628,6 @@ static inline int expand_downwards(struct vm_area_struct *vma,
          * is required to hold the mmap_sem in read mode.  We need the
          * anon_vma lock to serialize against concurrent expand_stacks.
          */
-        address &= PAGE_MASK;
-        error = 0;
 
         /* Somebody else might have raced and expanded it already */
         if (address < vma->vm_start) {