tools/mpremote: Prevent access outside mounted dir.

Signed-off-by: Damien George <damien@micropython.org>

tools/mpremote/src/mpremote/pyboardextended.py

@@ -1,4 +1,5 @@
 import os, re, serial, struct, time
+from errno import EPERM
 from .console import VT_ENABLED
 
 try:
@@ -262,7 +263,10 @@ def ilistdir(self, path):
         c = self.cmd
         c.begin(CMD_ILISTDIR_START)
         c.wr_str(self.path + path)
+        res = c.rd_s8()
         c.end()
+        if res < 0:
+            raise OSError(-res)
         def next():
             while True:
                 c.begin(CMD_ILISTDIR_NEXT)
@@ -350,13 +354,20 @@ def wr_str(self, s):
     def log_cmd(self, msg):
         print(f"[{msg}]", end="\r\n")
 
+    def path_check(self, path):
+        parent = os.path.realpath(self.root)
+        child = os.path.realpath(path)
+        if parent != os.path.commonpath([parent, child]):
+            raise OSError(EPERM, "")  # File is outside mounted dir
+
     def do_stat(self):
         path = self.root + self.rd_str()
         # self.log_cmd(f"stat {path}")
         try:
+            self.path_check(path)
             stat = os.stat(path)
         except OSError as er:
-            self.wr_s8(-abs(er.args[0]))
+            self.wr_s8(-abs(er.errno))
         else:
             self.wr_s8(0)
             # Note: st_ino would need to be 64-bit if added here
@@ -368,8 +379,14 @@ def do_stat(self):
 
     def do_ilistdir_start(self):
         path = self.root + self.rd_str()
-        self.data_ilistdir[0] = path
-        self.data_ilistdir[1] = os.listdir(path)
+        try:
+            self.path_check(path)
+            self.wr_s8(0)
+        except OSError as er:
+            self.wr_s8(-abs(er.errno))
+        else:
+            self.data_ilistdir[0] = path
+            self.data_ilistdir[1] = os.listdir(path)
 
     def do_ilistdir_next(self):
         if self.data_ilistdir[1]:
@@ -389,9 +406,10 @@ def do_open(self):
         mode = self.rd_str()
         # self.log_cmd(f"open {path} {mode}")
         try:
+            self.path_check(path)
             f = open(path, mode)
         except OSError as er:
-            self.wr_s8(-abs(er.args[0]))
+            self.wr_s8(-abs(er.errno))
         else:
             is_text = mode.find("b") == -1
             try:
@@ -437,21 +455,24 @@ def do_remove(self):
         path = self.root + self.rd_str()
         # self.log_cmd(f"remove {path}")
         try:
+            self.path_check(path)
             os.remove(path)
             ret = 0
         except OSError as er:
-            ret = -abs(er.args[0])
+            ret = -abs(er.errno)
         self.wr_s32(ret)
 
     def do_rename(self):
         old = self.root + self.rd_str()
         new = self.root + self.rd_str()
         # self.log_cmd(f"rename {old} {new}")
         try:
+            self.path_check(old)
+            self.path_check(new)
             os.rename(old, new)
             ret = 0
         except OSError as er:
-            ret = -abs(er.args[0])
+            ret = -abs(er.errno)
         self.wr_s32(ret)
 
     cmd_table = {