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# HG changeset patch
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# User Benjamin Peterson <benjamin@python.org>
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# Date 1389671978 18000
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# Node ID 87673659d8f7ba1623cd4914f09ad3d2ade034e9
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# Parent  2631d33ee7fbd5f0288931ef37872218d511d2e8
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complain when nbytes > buflen to fix possible buffer overflow (closes #20246)
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diff --git a/Lib/test/test_socket.py b/Lib/test/test_socket.py
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--- a/Lib/test/test_socket.py
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+++ b/Lib/test/test_socket.py
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@@ -1620,6 +1620,16 @@ class BufferIOTest(SocketConnectedTest):
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     _testRecvFromIntoMemoryview = _testRecvFromIntoArray
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+    def testRecvFromIntoSmallBuffer(self):
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+        # See issue #20246.
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+        buf = bytearray(8)
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+        self.assertRaises(ValueError, self.cli_conn.recvfrom_into, buf, 1024)
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+
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+    def _testRecvFromIntoSmallBuffer(self):
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+        with test_support.check_py3k_warnings():
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+            buf = buffer(MSG*2048)
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+        self.serv_conn.send(buf)
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+
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 TIPC_STYPE = 2000
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 TIPC_LOWER = 200
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diff --git a/Modules/socketmodule.c b/Modules/socketmodule.c
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--- a/Modules/socketmodule.c
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+++ b/Modules/socketmodule.c
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@@ -2742,6 +2742,10 @@ sock_recvfrom_into(PySocketSockObject *s
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     if (recvlen == 0) {
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         /* If nbytes was not specified, use the buffer's length */
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         recvlen = buflen;
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+    } else if (recvlen > buflen) {
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+        PyErr_SetString(PyExc_ValueError,
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+                        "nbytes is greater than the length of the buffer");
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+        goto error;
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     }
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     readlen = sock_recvfrom_guts(s, buf.buf, recvlen, flags, &addr);
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