Merge bitcoin/bitcoin#21644: p2p, bugfix: use NetPermissions::HasFlag() in CConnman::Bind()

36fb036 p2p: allow NetPermissions::ClearFlag() only with PF_ISIMPLICIT (Jon Atack)
4e0d578 test: add net permissions noban/download unit test coverage (Jon Atack)
dde69f2 p2p, bugfix: use NetPermissions::HasFlag() in CConnman::Bind() (Jon Atack)

Pull request description:

  This is a bugfix follow-up to #16248 and #19191 that was noticed in #21506. Both v0.21 and master are affected.

  Since #19191, noban is a multi-flag that implies download, so the conditional in `CConnman::Bind()` using a bitwise AND on noban will return the same result for both the noban status and the download status. This means that download peers are incorrectly not being added to local addresses because they are mistakenly seen as noban peers.

  The second commit adds unit test coverage to illustrate and test the noban/download relationship and the `NetPermissions` operations involving them.

  The final commit adds documentation and disallows calling `NetPermissions::ClearFlag()` with any second param other than `NetPermissionFlags` "implicit" -- per current usage in the codebase -- because `ClearFlag()` should not be called with any second param that is a subflag of a multiflag, e.g. "relay" or "download," as that would leave the result in an invalid state corresponding to none of the existing NetPermissionFlags. Thanks to Vasil Dimov for noticing this.

ACKs for top commit:
  theStack:
    re-ACK 36fb036 ☕
  vasild:
    ACK 36fb036
  hebasto:
    ACK 36fb036, I have reviewed the code and it looks OK, I agree it can be merged.
  kallewoof:
    Code review ACK 36fb036

Tree-SHA512: 5fbc7ddbf31d06b35bf238f4d77ef311e6b6ef2e1bb9893f32f889c1a0f65774a3710dcb21d94317fe6166df9334a9f2d42630809e7fe8cbd797dd6f6fc49491

Author: laanwj

src/net.cpp

@@ -2399,8 +2399,9 @@ NodeId CConnman::GetNewNodeId()
 
 
 bool CConnman::Bind(const CService &addr, unsigned int flags, NetPermissionFlags permissions) {
-    if (!(flags & BF_EXPLICIT) && !IsReachable(addr))
+    if (!(flags & BF_EXPLICIT) && !IsReachable(addr)) {
         return false;
+    }
     bilingual_str strError;
     if (!BindListenPort(addr, strError, permissions)) {
         if ((flags & BF_REPORT_ERROR) && clientInterface) {
@@ -2409,7 +2410,7 @@ bool CConnman::Bind(const CService &addr, unsigned int flags, NetPermissionFlags
         return false;
     }
 
-    if (addr.IsRoutable() && fDiscover && !(flags & BF_DONT_ADVERTISE) && !(permissions & PF_NOBAN)) {
+    if (addr.IsRoutable() && fDiscover && !(flags & BF_DONT_ADVERTISE) && !NetPermissions::HasFlag(permissions, NetPermissionFlags::PF_NOBAN)) {
         AddLocal(addr, LOCAL_BIND);
     }
 

src/net_permissions.h

@@ -51,8 +51,14 @@ class NetPermissions
     {
         flags = static_cast<NetPermissionFlags>(flags | f);
     }
+    //! ClearFlag is only called with `f` == NetPermissionFlags::PF_ISIMPLICIT.
+    //! If that should change in the future, be aware that ClearFlag should not
+    //! be called with a subflag of a multiflag, e.g. NetPermissionFlags::PF_RELAY
+    //! or NetPermissionFlags::PF_DOWNLOAD, as that would leave `flags` in an
+    //! invalid state corresponding to none of the existing flags.
     static inline void ClearFlag(NetPermissionFlags& flags, NetPermissionFlags f)
     {
+        assert(f == NetPermissionFlags::PF_ISIMPLICIT);
         flags = static_cast<NetPermissionFlags>(flags & ~f);
     }
 };

src/test/fuzz/net_permissions.cpp

@@ -25,7 +25,7 @@ FUZZ_TARGET(net_permissions)
         (void)NetPermissions::ToStrings(net_whitebind_permissions.m_flags);
         (void)NetPermissions::AddFlag(net_whitebind_permissions.m_flags, net_permission_flags);
         assert(NetPermissions::HasFlag(net_whitebind_permissions.m_flags, net_permission_flags));
-        (void)NetPermissions::ClearFlag(net_whitebind_permissions.m_flags, net_permission_flags);
+        (void)NetPermissions::ClearFlag(net_whitebind_permissions.m_flags, NetPermissionFlags::PF_ISIMPLICIT);
         (void)NetPermissions::ToStrings(net_whitebind_permissions.m_flags);
     }
 
@@ -35,7 +35,7 @@ FUZZ_TARGET(net_permissions)
         (void)NetPermissions::ToStrings(net_whitelist_permissions.m_flags);
         (void)NetPermissions::AddFlag(net_whitelist_permissions.m_flags, net_permission_flags);
         assert(NetPermissions::HasFlag(net_whitelist_permissions.m_flags, net_permission_flags));
-        (void)NetPermissions::ClearFlag(net_whitelist_permissions.m_flags, net_permission_flags);
+        (void)NetPermissions::ClearFlag(net_whitelist_permissions.m_flags, NetPermissionFlags::PF_ISIMPLICIT);
         (void)NetPermissions::ToStrings(net_whitelist_permissions.m_flags);
     }
 }

src/test/netbase_tests.cpp

@@ -395,6 +395,28 @@ BOOST_AUTO_TEST_CASE(netpermissions_test)
     BOOST_CHECK(NetWhitebindPermissions::TryParse("@1.2.3.4:32", whitebindPermissions, error));
     BOOST_CHECK_EQUAL(whitebindPermissions.m_flags, PF_NONE);
 
+    NetWhitebindPermissions noban, noban_download, download_noban, download;
+
+    // "noban" implies "download"
+    BOOST_REQUIRE(NetWhitebindPermissions::TryParse("[email protected]:32", noban, error));
+    BOOST_CHECK_EQUAL(noban.m_flags, NetPermissionFlags::PF_NOBAN);
+    BOOST_CHECK(NetPermissions::HasFlag(noban.m_flags, NetPermissionFlags::PF_DOWNLOAD));
+    BOOST_CHECK(NetPermissions::HasFlag(noban.m_flags, NetPermissionFlags::PF_NOBAN));
+
+    // "noban,download" is equivalent to "noban"
+    BOOST_REQUIRE(NetWhitebindPermissions::TryParse("noban,[email protected]:32", noban_download, error));
+    BOOST_CHECK_EQUAL(noban_download.m_flags, noban.m_flags);
+
+    // "download,noban" is equivalent to "noban"
+    BOOST_REQUIRE(NetWhitebindPermissions::TryParse("download,[email protected]:32", download_noban, error));
+    BOOST_CHECK_EQUAL(download_noban.m_flags, noban.m_flags);
+
+    // "download" excludes (does not imply) "noban"
+    BOOST_REQUIRE(NetWhitebindPermissions::TryParse("[email protected]:32", download, error));
+    BOOST_CHECK_EQUAL(download.m_flags, NetPermissionFlags::PF_DOWNLOAD);
+    BOOST_CHECK(NetPermissions::HasFlag(download.m_flags, NetPermissionFlags::PF_DOWNLOAD));
+    BOOST_CHECK(!NetPermissions::HasFlag(download.m_flags, NetPermissionFlags::PF_NOBAN));
+
     // Happy path, can parse flags
     BOOST_CHECK(NetWhitebindPermissions::TryParse("bloom,[email protected]:32", whitebindPermissions, error));
     // forcerelay should also activate the relay permission
@@ -407,7 +429,7 @@ BOOST_AUTO_TEST_CASE(netpermissions_test)
 
     // Allow dups
     BOOST_CHECK(NetWhitebindPermissions::TryParse("bloom,relay,noban,[email protected]:32", whitebindPermissions, error));
-    BOOST_CHECK_EQUAL(whitebindPermissions.m_flags, PF_BLOOMFILTER | PF_RELAY | PF_NOBAN);
+    BOOST_CHECK_EQUAL(whitebindPermissions.m_flags, PF_BLOOMFILTER | PF_RELAY | PF_NOBAN | PF_DOWNLOAD); // "noban" implies "download"
 
     // Allow empty
     BOOST_CHECK(NetWhitebindPermissions::TryParse("bloom,relay,,[email protected]:32", whitebindPermissions, error));
@@ -428,6 +450,8 @@ BOOST_AUTO_TEST_CASE(netpermissions_test)
     // Happy path for whitelist parsing
     BOOST_CHECK(NetWhitelistPermissions::TryParse("[email protected]", whitelistPermissions, error));
     BOOST_CHECK_EQUAL(whitelistPermissions.m_flags, PF_NOBAN);
+    BOOST_CHECK(NetPermissions::HasFlag(whitelistPermissions.m_flags, NetPermissionFlags::PF_NOBAN));
+
     BOOST_CHECK(NetWhitelistPermissions::TryParse("bloom,forcerelay,noban,[email protected]/32", whitelistPermissions, error));
     BOOST_CHECK_EQUAL(whitelistPermissions.m_flags, PF_BLOOMFILTER | PF_FORCERELAY | PF_NOBAN | PF_RELAY);
     BOOST_CHECK(error.empty());