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

4 files changed, 17 insertions, 0 deletions

diff --git a/Lib/test/test_socket.py b/Lib/test/test_socket.py
index 6a9497bc7d..c242a57991 100644
--- a/Lib/test/test_socket.py
+++ b/Lib/test/test_socket.py
@@ -1424,6 +1424,14 @@ class BufferIOTest(SocketConnectedTest):
         buf = bytes(MSG)
         self.serv_conn.send(buf)
 
+    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 e74324f112..0de41015b6 100644
--- a/Misc/ACKS
+++ b/Misc/ACKS
@@ -757,6 +757,7 @@ Kragen Sitaker
 Eric V. Smith
 Christopher Smith
 Gregory P. Smith
+Ryan Smith-Roberts
 Rafal Smotrzyk
 Dirk Soede
 Paul Sokolovsky
diff --git a/Misc/NEWS b/Misc/NEWS
index d3f8b2ff86..437acbf33f 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -13,6 +13,8 @@ Core and Builtins
 Library
 -------
 
+- Issue #20246: Fix buffer overflow in socket.recvfrom_into.
+
 - Issue #19435: Fix directory traversal attack on CGIHttpRequestHandler.
 
 - Issue #14984: On POSIX systems, when netrc is called without a filename
diff --git a/Modules/socketmodule.c b/Modules/socketmodule.c
index 5e911e0584..ebaebf51d1 100644
--- a/Modules/socketmodule.c
+++ b/Modules/socketmodule.c
@@ -2494,6 +2494,12 @@ 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);
+        Py_XDECREF(addr);
+        PyErr_SetString(PyExc_ValueError,
+                        "nbytes is greater than the length of the buffer");
+        return NULL;
     }
 
     readlen = sock_recvfrom_guts(s, buf, recvlen, flags, &addr);