bpo-41004: Resolve hash collisions for IPv4Interface and IPv6Interface (GH-21033)

The __hash__() methods of classes IPv4Interface and IPv6Interface had issue
of generating constant hash values of 32 and 128 respectively causing hash collisions.
The fix uses the hash() function to generate hash values for the objects
instead of XOR operation
(cherry picked from commit b30ee26)

Co-authored-by: Ravi Teja P <[email protected]>

Author: miss-islington

Lib/ipaddress.py

@@ -1420,7 +1420,7 @@ def __lt__(self, other):
             return False
 
     def __hash__(self):
-        return self._ip ^ self._prefixlen ^ int(self.network.network_address)
+        return hash((self._ip, self._prefixlen, int(self.network.network_address)))
 
     __reduce__ = _IPAddressBase.__reduce__
 
@@ -2120,7 +2120,7 @@ def __lt__(self, other):
             return False
 
     def __hash__(self):
-        return self._ip ^ self._prefixlen ^ int(self.network.network_address)
+        return hash((self._ip, self._prefixlen, int(self.network.network_address)))
 
     __reduce__ = _IPAddressBase.__reduce__
 

Lib/test/test_ipaddress.py

@@ -2548,6 +2548,18 @@ def testsixtofour(self):
                          sixtofouraddr.sixtofour)
         self.assertFalse(bad_addr.sixtofour)
 
+    # issue41004 Hash collisions in IPv4Interface and IPv6Interface
+    def testV4HashIsNotConstant(self):
+        ipv4_address1 = ipaddress.IPv4Interface("1.2.3.4")
+        ipv4_address2 = ipaddress.IPv4Interface("2.3.4.5")
+        self.assertNotEqual(ipv4_address1.__hash__(), ipv4_address2.__hash__())
+
+    # issue41004 Hash collisions in IPv4Interface and IPv6Interface
+    def testV6HashIsNotConstant(self):
+        ipv6_address1 = ipaddress.IPv6Interface("2001:658:22a:cafe:200:0:0:1")
+        ipv6_address2 = ipaddress.IPv6Interface("2001:658:22a:cafe:200:0:0:2")
+        self.assertNotEqual(ipv6_address1.__hash__(), ipv6_address2.__hash__())
+
 
 if __name__ == '__main__':
     unittest.main()

Misc/NEWS.d/next/Security/2020-06-29-16-02-29.bpo-41004.ovF0KZ.rst

@@ -0,0 +1 @@
+The __hash__() methods of  ipaddress.IPv4Interface and ipaddress.IPv6Interface incorrectly generated constant hash values of 32 and 128 respectively. This resulted in always causing hash collisions. The fix uses hash() to generate hash values for the tuple of (address, mask length, network address).