Explicitly check for TTL expiration when using Ping utility (#65312)

* Explicitly check for TTL expiration when using Ping utility

* Fixes

* Improve the implementation

src/libraries/System.Net.Ping/src/System/Net/NetworkInformation/Ping.PingUtility.cs

@@ -53,15 +53,15 @@ private PingReply SendWithPingUtility(IPAddress address, byte[] buffer, int time
             using (Process p = GetPingProcess(address, buffer, timeout, options))
             {
                 p.Start();
-                if (!p.WaitForExit(timeout) || p.ExitCode == 1 || p.ExitCode == 2)
+                if (!p.WaitForExit(timeout))
                 {
                     return CreatePingReply(IPStatus.TimedOut);
                 }
 
                 try
                 {
-                    string output = p.StandardOutput.ReadToEnd();
-                    return ParsePingUtilityOutput(address, output);
+                    string stdout = p.StandardOutput.ReadToEnd();
+                    return ParsePingUtilityOutput(address, p.ExitCode, stdout);
                 }
                 catch (Exception)
                 {
@@ -90,16 +90,10 @@ private async Task<PingReply> SendWithPingUtilityAsync(IPAddress address, byte[]
                     return CreatePingReply(IPStatus.TimedOut);
                 }
 
-                if (p.ExitCode == 1 || p.ExitCode == 2)
-                {
-                    // Throw timeout for known failure return codes from ping functions.
-                    return CreatePingReply(IPStatus.TimedOut);
-                }
-
                 try
                 {
-                    string output = await p.StandardOutput.ReadToEndAsync().ConfigureAwait(false);
-                    return ParsePingUtilityOutput(address, output);
+                    string stdout = await p.StandardOutput.ReadToEndAsync().ConfigureAwait(false);
+                    return ParsePingUtilityOutput(address, p.ExitCode, stdout);
                 }
                 catch (Exception)
                 {
@@ -109,15 +103,47 @@ private async Task<PingReply> SendWithPingUtilityAsync(IPAddress address, byte[]
             }
         }
 
-        private PingReply ParsePingUtilityOutput(IPAddress address, string output)
+        private static PingReply ParsePingUtilityOutput(IPAddress address, int exitCode, string stdout)
         {
-            long rtt = UnixCommandLinePing.ParseRoundTripTime(output);
-            return new PingReply(
-                address,
-                null, // Ping utility cannot accommodate these, return null to indicate they were ignored.
-                IPStatus.Success,
-                rtt,
-                Array.Empty<byte>()); // Ping utility doesn't deliver this info.
+            // Throw timeout for known failure return codes from ping functions.
+            if (exitCode == 1 || exitCode == 2)
+            {
+                // TTL exceeded may have occured
+                if (TryParseTtlExceeded(stdout, out PingReply? reply))
+                {
+                    return reply!;
+                }
+
+                // otherwise assume timeout
+                return CreatePingReply(IPStatus.TimedOut);
+            }
+
+            // On success, report RTT
+            long rtt = UnixCommandLinePing.ParseRoundTripTime(stdout);
+            return CreatePingReply(IPStatus.Success, address, rtt);
+        }
+
+        private static bool TryParseTtlExceeded(string stdout, out PingReply? reply)
+        {
+            reply = null;
+            if (!stdout.Contains("Time to live exceeded", StringComparison.Ordinal))
+            {
+                return false;
+            }
+
+            // look for address in "From 172.21.64.1 icmp_seq=1 Time to live exceeded"
+            int addressStart = stdout.IndexOf("From ", StringComparison.Ordinal) + 5;
+            int addressLength = stdout.IndexOf(' ', Math.Max(addressStart, 0)) - addressStart;
+            IPAddress? address;
+            if (addressStart < 5 || addressLength <= 0 || !IPAddress.TryParse(stdout.AsSpan(addressStart, addressLength), out address))
+            {
+                // failed to parse source address (which in case of TTL is different than the original
+                // destination address), fallback to all 0
+                address = new IPAddress(0);
+            }
+
+            reply = CreatePingReply(IPStatus.TimeExceeded, address);
+            return true;
         }
     }
 }

src/libraries/System.Net.Ping/src/System/Net/NetworkInformation/Ping.RawSocket.cs

@@ -32,10 +32,10 @@ private unsafe SocketConfig GetSocketConfig(IPAddress address, byte[] buffer, in
             bool sendIpHeader = ipv4 && options != null && SendIpHeader;
             int totalLength = 0;
 
-             if (sendIpHeader)
-             {
+            if (sendIpHeader)
+            {
                 iph.VersionAndLength = 0x45;
-                totalLength = sizeof(IpHeader) + checked(sizeof(IcmpHeader) +  buffer.Length);
+                totalLength = sizeof(IpHeader) + checked(sizeof(IcmpHeader) + buffer.Length);
                 // On OSX this strangely must be host byte order.
                 iph.TotalLength = OperatingSystem.IsFreeBSD() ? (ushort)IPAddress.HostToNetworkOrder((short)totalLength) : (ushort)totalLength;
                 iph.Protocol = 1; // ICMP
@@ -46,7 +46,7 @@ private unsafe SocketConfig GetSocketConfig(IPAddress address, byte[] buffer, in
 #pragma warning restore 618
                 // No need to fill in SourceAddress or checksum.
                 // If left blank, kernel will fill it in - at least on OSX.
-             }
+            }
 
             return new SocketConfig(
                 new IPEndPoint(address, 0), timeout, options,
@@ -340,11 +340,11 @@ private async Task<PingReply> SendIcmpEchoRequestOverRawSocketAsync(IPAddress ad
             }
         }
 
-        private static PingReply CreatePingReply(IPStatus status)
+        private static PingReply CreatePingReply(IPStatus status, IPAddress? address = null, long rtt = 0)
         {
             // Documentation indicates that you should only pay attention to the IPStatus value when
             // its value is not "Success", but the rest of these values match that of the Windows implementation.
-            return new PingReply(new IPAddress(0), null, status, 0, Array.Empty<byte>());
+            return new PingReply(address ?? new IPAddress(0), null, status, rtt, Array.Empty<byte>());
         }
 
 #if DEBUG