[#3712] Avoid assert on empty packet

/src/lib/dhcp/pkt_filter_lpf.cc
    PktFilterLPF::receive() - throw if packet has no data

/src/lib/util/buffer.h
    InputBuffer::readVecotr() - avoid peek if read request length is 0

/src/lib/util/tests/buffer_unittest.cc
    Updated test

Author: tmarkwalder

src/lib/dhcp/pkt_filter_lpf.cc

@@ -318,9 +318,14 @@ PktFilterLPF::receive(Iface& iface, const SocketInfo& socket_info) {
     decodeEthernetHeader(buf, dummy_pkt);
     decodeIpUdpHeader(buf, dummy_pkt);
 
+    auto v4_len = buf.getLength() - buf.getPosition();
+    if (v4_len <= 0) {
+        isc_throw(SocketReadError, "Pkt4FilterLpf:: packet has no DHCPv4 data");
+    }
+
     // Read the DHCP data.
     std::vector<uint8_t> dhcp_buf;
-    buf.readVector(dhcp_buf, buf.getLength() - buf.getPosition());
+    buf.readVector(dhcp_buf, v4_len);
 
     // Decode DHCP data into the Pkt4 object.
     Pkt4Ptr pkt = Pkt4Ptr(new Pkt4(&dhcp_buf[0], dhcp_buf.size()));
@@ -344,8 +349,7 @@ PktFilterLPF::receive(Iface& iface, const SocketInfo& socket_info) {
 
             struct timeval cmsg_time;
             memcpy(&cmsg_time, CMSG_DATA(cmsg), sizeof(cmsg_time));
-            pkt->addPktEvent(PktEvent::SOCKET_RECEIVED, cmsg_time);
-            break;
+            pkt->addPktEvent(PktEvent::SOCKET_RECEIVED, cmsg_time); break;
         }
 
         cmsg = CMSG_NXTHDR(&m, cmsg);

src/lib/util/buffer.h

@@ -1,4 +1,4 @@
-// Copyright (C) 2009-2024 Internet Systems Consortium, Inc. ("ISC")
+// Copyright (C) 2009-2025 Internet Systems Consortium, Inc. ("ISC")
 //
 // This Source Code Form is subject to the terms of the Mozilla Public
 // License, v. 2.0. If a copy of the MPL was not distributed with this
@@ -233,7 +233,8 @@ class InputBuffer {
     /// @details If specified buffer is too short, it will be expanded using
     /// vector::resize() method. If the remaining length of the buffer
     /// is smaller than the specified length, an exception of class
-    /// @c isc::OutOfRange will be thrown.
+    /// @c isc::OutOfRange will be thrown.  Read length zero results
+    /// in an empty vector.
     ///
     /// @param data Reference to a buffer (data will be stored there).
     /// @param len Size specified number of bytes to read in a vector.
@@ -244,7 +245,9 @@ class InputBuffer {
         }
 
         data.resize(len);
-        peekData(&data[0], len);
+        if (len) {
+            peekData(&data[0], len);
+        }
     }
 
     /// @brief Read specified number of bytes as a vector.

src/lib/util/tests/buffer_unittest.cc

@@ -1,4 +1,4 @@
-// Copyright (C) 2009-2024 Internet Systems Consortium, Inc. ("ISC")
+// Copyright (C) 2009-2025 Internet Systems Consortium, Inc. ("ISC")
 //
 // This Source Code Form is subject to the terms of the Mozilla Public
 // License, v. 2.0. If a copy of the MPL was not distributed with this
@@ -197,6 +197,12 @@ TEST_F(BufferTest, inputBufferRead) {
     ASSERT_EQ(sizeof(vdata), datav.size());
     ASSERT_EQ(0, memcmp(&vdata[0], testdata, sizeof(testdata)));
     ASSERT_EQ(sizeof(vdata), ibuffer.getPosition());
+
+    // Verify that read len of zero results in an empty
+    // vector without throwing.
+    datav.resize(8);
+    ASSERT_NO_THROW(ibuffer.readVector(datav, 0));
+    ASSERT_EQ(datav.size(), 0);
 }
 
 TEST_F(BufferTest, outputBufferReadAt) {