[Python-checkins] bpo-41004: Resolve hash collisions for IPv4Interface and IPv6Interface (GH-21033)

[Ravi Teja P]

https://github.com/python/cpython/commit/b30ee26e366bf509b7538d79bfec6c6d38d53f28
commit: b30ee26e366bf509b7538d79bfec6c6d38d53f28
branch: master
author: Ravi Teja P <rvteja92 at gmail.com>
committer: GitHub <noreply at github.com>
date: 2020-06-29T13:39:29-04:00
summary:

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

files:
A Misc/NEWS.d/next/Security/2020-06-29-16-02-29.bpo-41004.ovF0KZ.rst
M Lib/ipaddress.py
M Lib/test/test_ipaddress.py

diff --git a/Lib/ipaddress.py b/Lib/ipaddress.py
index 6e5a754c2acf1..75b4c352c1d25 100644
--- a/Lib/ipaddress.py
+++ b/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__
 
diff --git a/Lib/test/test_ipaddress.py b/Lib/test/test_ipaddress.py
index 6d5814c9774a0..3c070080a6aae 100644
--- a/Lib/test/test_ipaddress.py
+++ b/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()
diff --git a/Misc/NEWS.d/next/Security/2020-06-29-16-02-29.bpo-41004.ovF0KZ.rst b/Misc/NEWS.d/next/Security/2020-06-29-16-02-29.bpo-41004.ovF0KZ.rst
new file mode 100644
index 0000000000000..1380b31fbe9f4
--- /dev/null
+++ b/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).