fix: _NoAddress.__eq__ unconditionally returns True

Closes #3014

CHANGELOG.md

@@ -14,6 +14,8 @@
 - fix lots of linter errors identified by pyright @williballenthin #3052
 - fix: elf.py vdso_guess exception handler clobbers symtab_guess @williballenthin #3013
 
+- fix: _NoAddress.__eq__ unconditionally returns True @williballenthin #3014
+
 ### capa Explorer Web
 
 ### capa Explorer IDA Pro plugin

capa/features/address.py

@@ -184,7 +184,7 @@ class DNTokenOffsetAddress(Address):
 
 class _NoAddress(Address):
     def __eq__(self, other):
-        return True
+        return isinstance(other, _NoAddress)
 
     def __lt__(self, other):
         return False
@@ -195,7 +195,7 @@ class _NoAddress(Address):
         return other is not self
 
     def __hash__(self):
-        return hash(0)
+        return hash(None)
 
     def __repr__(self):
         return "no address"

tests/test_engine.py

@@ -22,6 +22,30 @@ ADDR3 = capa.features.address.AbsoluteVirtualAddress(0x401003)
 ADDR4 = capa.features.address.AbsoluteVirtualAddress(0x401004)
 
 
+def test_no_address_equality():
+    no_addr = capa.features.address.NO_ADDRESS
+    addr_zero = capa.features.address.AbsoluteVirtualAddress(0)
+
+    assert no_addr == no_addr
+    assert no_addr != addr_zero
+    assert addr_zero != no_addr
+    assert no_addr != ADDR1
+
+
+def test_no_address_hash():
+    no_addr = capa.features.address.NO_ADDRESS
+    addr_zero = capa.features.address.AbsoluteVirtualAddress(0)
+
+    assert hash(no_addr) != hash(addr_zero)
+
+    s = {no_addr, addr_zero}
+    assert len(s) == 2
+
+    d = {no_addr: "no", addr_zero: "zero"}
+    assert d[no_addr] == "no"
+    assert d[addr_zero] == "zero"
+
+
 def test_number():
     assert bool(Number(1).evaluate({Number(0): {ADDR1}})) is False
     assert bool(Number(1).evaluate({Number(1): {ADDR1}})) is True