mremap: don't leak new_vma if f_op->mremap() fails

move_vma() can't just return if f_op->mremap() fails, we should unmap the
new vma like we do if move_page_tables() fails.  To avoid the code
duplication this patch moves the "move entries back" under the new "if
(err)" branch.

Signed-off-by: Oleg Nesterov <[email protected]>
Acked-by: David Rientjes <[email protected]>
Cc: Benjamin LaHaise <[email protected]>
Cc: Hugh Dickins <[email protected]>
Cc: Jeff Moyer <[email protected]>
Cc: Kirill Shutemov <[email protected]>
Cc: Pavel Emelyanov <[email protected]>
Cc: Laurent Dufour <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

mm/mremap.c

@@ -276,6 +276,12 @@ static unsigned long move_vma(struct vm_area_struct *vma,
 	moved_len = move_page_tables(vma, old_addr, new_vma, new_addr, old_len,
 				     need_rmap_locks);
 	if (moved_len < old_len) {
+		err = -ENOMEM;
+	} else if (vma->vm_file && vma->vm_file->f_op->mremap) {
+		err = vma->vm_file->f_op->mremap(vma->vm_file, new_vma);
+	}
+
+	if (unlikely(err)) {
 		/*
 		 * On error, move entries back from new area to old,
 		 * which will succeed since page tables still there,
@@ -286,16 +292,8 @@ static unsigned long move_vma(struct vm_area_struct *vma,
 		vma = new_vma;
 		old_len = new_len;
 		old_addr = new_addr;
-		new_addr = -ENOMEM;
+		new_addr = err;
 	} else {
-		if (vma->vm_file && vma->vm_file->f_op->mremap) {
-			err = vma->vm_file->f_op->mremap(vma->vm_file, new_vma);
-			if (err < 0) {
-				move_page_tables(new_vma, new_addr, vma,
-						 old_addr, moved_len, true);
-				return err;
-			}
-		}
 		arch_remap(mm, old_addr, old_addr + old_len,
 			   new_addr, new_addr + new_len);
 	}