From 1c6b8752b891c1a25524d8dfaa8efb7176c0dbec Mon Sep 17 00:00:00 2001
From: Andrew Morgan <1342360+anoadragon453@users.noreply.github.com>
Date: Tue, 29 Sep 2020 12:36:44 +0100
Subject: [PATCH] Only assert valid next_link params when provided (#8417)

Broken in https://github.com/matrix-org/synapse/pull/8275 and has yet to be put in a release. Fixes https://github.com/matrix-org/synapse/issues/8418.

`next_link` is an optional parameter. However, we were checking whether the `next_link` param was valid, even if it wasn't provided. In that case, `next_link` was `None`, which would clearly not be a valid URL.

This would prevent password reset and other operations if `next_link` was not provided, and the `next_link_domain_whitelist` config option was set.
---
 changelog.d/8417.feature                   |  1 +
 synapse/rest/client/v2_alpha/account.py    | 15 +++++++++------
 tests/rest/client/v2_alpha/test_account.py |  6 ++++++
 3 files changed, 16 insertions(+), 6 deletions(-)
 create mode 100644 changelog.d/8417.feature

diff --git a/changelog.d/8417.feature b/changelog.d/8417.feature
new file mode 100644
index 000000000000..17549c3df39a
--- /dev/null
+++ b/changelog.d/8417.feature
@@ -0,0 +1 @@
+Add a config option to specify a whitelist of domains that a user can be redirected to after validating their email or phone number.
\ No newline at end of file
diff --git a/synapse/rest/client/v2_alpha/account.py b/synapse/rest/client/v2_alpha/account.py
index c3ce0f62592a..9245214f36eb 100644
--- a/synapse/rest/client/v2_alpha/account.py
+++ b/synapse/rest/client/v2_alpha/account.py
@@ -103,8 +103,9 @@ async def on_POST(self, request):
                 Codes.THREEPID_DENIED,
             )
 
-        # Raise if the provided next_link value isn't valid
-        assert_valid_next_link(self.hs, next_link)
+        if next_link:
+            # Raise if the provided next_link value isn't valid
+            assert_valid_next_link(self.hs, next_link)
 
         # The email will be sent to the stored address.
         # This avoids a potential account hijack by requesting a password reset to
@@ -379,8 +380,9 @@ async def on_POST(self, request):
                 Codes.THREEPID_DENIED,
             )
 
-        # Raise if the provided next_link value isn't valid
-        assert_valid_next_link(self.hs, next_link)
+        if next_link:
+            # Raise if the provided next_link value isn't valid
+            assert_valid_next_link(self.hs, next_link)
 
         existing_user_id = await self.store.get_user_id_by_threepid("email", email)
 
@@ -453,8 +455,9 @@ async def on_POST(self, request):
                 Codes.THREEPID_DENIED,
             )
 
-        # Raise if the provided next_link value isn't valid
-        assert_valid_next_link(self.hs, next_link)
+        if next_link:
+            # Raise if the provided next_link value isn't valid
+            assert_valid_next_link(self.hs, next_link)
 
         existing_user_id = await self.store.get_user_id_by_threepid("msisdn", msisdn)
 
diff --git a/tests/rest/client/v2_alpha/test_account.py b/tests/rest/client/v2_alpha/test_account.py
index 93f899d86133..ae2cd67f35de 100644
--- a/tests/rest/client/v2_alpha/test_account.py
+++ b/tests/rest/client/v2_alpha/test_account.py
@@ -732,6 +732,12 @@ def test_next_link_file_uri(self):
     @override_config({"next_link_domain_whitelist": ["example.com", "example.org"]})
     def test_next_link_domain_whitelist(self):
         """Tests next_link parameters must fit the whitelist if provided"""
+
+        # Ensure not providing a next_link parameter still works
+        self._request_token(
+            "something@example.com", "some_secret", next_link=None, expect_code=200,
+        )
+
         self._request_token(
             "something@example.com",
             "some_secret",