Add test validating against regression in #46469 (#47643)

* Add test validating against regression in #46469

* fix test bug

src/libraries/System.Diagnostics.Process/tests/ProcessTests.Unix.cs

@@ -4,6 +4,7 @@
 using System.Collections;
 using System.Collections.Generic;
 using System.ComponentModel;
+using System.Globalization;
 using System.IO;
 using System.Linq;
 using System.Reflection;
@@ -802,6 +803,24 @@ public void TestProcessRecycledPid()
             Assert.True(foundRecycled);
         }
 
+        [PlatformSpecific(TestPlatforms.AnyUnix)]
+        [ConditionalTheory(typeof(RemoteExecutor), nameof(RemoteExecutor.IsSupported))]
+        [InlineData("/dev/stdin",  O_RDONLY)]
+        [InlineData("/dev/stdout", O_WRONLY)]
+        [InlineData("/dev/stderr", O_WRONLY)]
+        public void ChildProcessRedirectedIO_FilePathOpenShouldSucceed(string filename, int flags)
+        {
+            var options = new RemoteInvokeOptions { StartInfo = new ProcessStartInfo { RedirectStandardOutput = true, RedirectStandardInput = true, RedirectStandardError = true }};
+            using (RemoteInvokeHandle handle = RemoteExecutor.Invoke(ExecuteChildProcess, filename, flags.ToString(CultureInfo.InvariantCulture), options))
+            { }
+
+            static void ExecuteChildProcess(string filename, string flags)
+            {
+                int result = open(filename, int.Parse(flags, CultureInfo.InvariantCulture));
+                Assert.True(result >= 0, $"failed to open file with {result} and errno {Marshal.GetLastWin32Error()}.");
+            }
+        }
+
         [ConditionalTheory(typeof(RemoteExecutor), nameof(RemoteExecutor.IsSupported))]
         [InlineData(true)]
         [InlineData(false)]
@@ -941,6 +960,12 @@ private static unsafe HashSet<uint> GetGroups()
         [DllImport("libc", SetLastError = true)]
         private static extern int kill(int pid, int sig);
 
+        [DllImport("libc", SetLastError = true)]
+        private static extern int open(string pathname, int flags);
+
+        private const int O_RDONLY = 0;
+        private const int O_WRONLY = 1;
+
         private static readonly string[] s_allowedProgramsToRun = new string[] { "xdg-open", "gnome-open", "kfmclient" };
 
         private string WriteScriptFile(string directory, string name, int returnValue)