👌 fix possible ReDOS in newline rule (#275)

Implements upstream: markdown-it/markdown-it@ffc49ab

Author: chrisjsewell

markdown_it/port.yaml

@@ -1,7 +1,7 @@
 - package: markdown-it/markdown-it
-  version: 12.3.1
-  commit: 76469e83dc1a1e3ed943b483b554003a666bddf7
-  date: Jan 7, 2022
+  version: 12.3.2
+  commit: d72c68b520cedacae7878caa92bf7fe32e3e0e6f
+  date: Jan 8, 2022
   notes:
     - Rename variables that use python built-in names, e.g.
       - `max` -> `maximum`

markdown_it/rules_inline/newline.py

@@ -1,11 +1,7 @@
-# Proceess '\n'
-import re
-
+"""Proceess '\n'."""
 from ..common.utils import charStrAt, isStrSpace
 from .state_inline import StateInline
 
-endSpace = re.compile(r" +$")
-
 
 def newline(state: StateInline, silent: bool) -> bool:
     pos = state.pos
@@ -23,7 +19,12 @@ def newline(state: StateInline, silent: bool) -> bool:
     if not silent:
         if pmax >= 0 and charStrAt(state.pending, pmax) == " ":
             if pmax >= 1 and charStrAt(state.pending, pmax - 1) == " ":
-                state.pending = endSpace.sub("", state.pending)
+                # Find whitespaces tail of pending chars.
+                ws = pmax - 1
+                while ws >= 1 and charStrAt(state.pending, ws - 1) == " ":
+                    ws -= 1
+                state.pending = state.pending[:ws]
+
                 state.push("hardbreak", "br", 0)
             else:
                 state.pending = state.pending[:-1]