complain when nbytes > buflen to fix possible buffer overflow (closes #20246)

4 files changed, 16 insertions, 0 deletions

diff --git a/Lib/test/test_socket.py b/Lib/test/test_socket.py
index 4ecab952d0..290c4dd096 100644
--- a/Lib/test/test_socket.py
+++ b/Lib/test/test_socket.py
@@ -1968,6 +1968,14 @@ class BufferIOTest(SocketConnectedTest):
 
     _testRecvFromIntoMemoryview = _testRecvFromIntoArray
 
+    def testRecvFromIntoSmallBuffer(self):
+        # See issue #20246.
+        buf = bytearray(8)
+        self.assertRaises(ValueError, self.cli_conn.recvfrom_into, buf, 1024)
+
+    def _testRecvFromIntoSmallBuffer(self):
+        self.serv_conn.send(MSG*2048)
+
 
 TIPC_STYPE = 2000
 TIPC_LOWER = 200
diff --git a/Misc/ACKS b/Misc/ACKS
index 6ea3f78d76..5236e1066b 100644
--- a/Misc/ACKS
+++ b/Misc/ACKS
@@ -1020,6 +1020,7 @@ Eric V. Smith
 Christopher Smith
 Gregory P. Smith
 Roy Smith
+Ryan Smith-Roberts
 Rafal Smotrzyk
 Dirk Soede
 Paul Sokolovsky
diff --git a/Misc/NEWS b/Misc/NEWS
index 430bec2cfa..693a0c8076 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -10,6 +10,8 @@ What's New in Python 3.2.6?
 Library
 -------
 
+- Issue #20246: Fix buffer overflow in socket.recvfrom_into.
+
 - Issue #12226: HTTPS is now used by default when connecting to PyPI.
 
 - Issue #19435: Fix directory traversal attack on CGIHttpRequestHandler.
diff --git a/Modules/socketmodule.c b/Modules/socketmodule.c
index e027625024..903e10c98c 100644
--- a/Modules/socketmodule.c
+++ b/Modules/socketmodule.c
@@ -2598,6 +2598,11 @@ sock_recvfrom_into(PySocketSockObject *s, PyObject *args, PyObject* kwds)
     if (recvlen == 0) {
         /* If nbytes was not specified, use the buffer's length */
         recvlen = buflen;
+    } else if (recvlen > buflen) {
+        PyBuffer_Release(&pbuf);
+        PyErr_SetString(PyExc_ValueError,
+                        "nbytes is greater than the length of the buffer");
+        return NULL;
     }
 
     readlen = sock_recvfrom_guts(s, buf, recvlen, flags, &addr);