p2p: allow NetPermissions::ClearFlag() only with PF_ISIMPLICIT

NetPermissions::ClearFlag() is currently only called in the codebase with
an `f` value of NetPermissionFlags::PF_ISIMPLICIT.

If that should change in the future, ClearFlag() should not be called
with `f` being 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 NetPermissionFlags.

Therefore, allow only calling ClearFlag with the implicit flag for now.

Co-authored-by: Vasil Dimov <vd@FreeBSD.org>

2 files changed, 8 insertions, 2 deletions

diff --git a/src/net_permissions.h b/src/net_permissions.h
index bba0ea1695..142b317bf6 100644
--- a/src/net_permissions.h
+++ b/src/net_permissions.h
@@ -51,8 +51,14 @@ public:
     {
         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);
     }
 };
diff --git a/src/test/fuzz/net_permissions.cpp b/src/test/fuzz/net_permissions.cpp
index 544a33047b..6fdf4b653c 100644
--- a/src/test/fuzz/net_permissions.cpp
+++ b/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);
     }
 }