security: protect from stack expantion into low vm addresses

eparis · James Morris · commit 8869477a49c3 · 2007-12-06T00:24:48.000+11:00
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 &lt;eparis@redhat.com&gt;
Signed-off-by: James Morris &lt;jmorris@namei.org&gt;
diff --git a/mm/mmap.c b/mm/mmap.c
@@ -1615,15 +1615,19 @@ 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);
 
 	/*
 	 * vma->vm_start/vm_end cannot change under us because the caller
 	 * 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) {
