From c1d6ad1d1556ec0cd55fbe2073f2831487fcc10a Mon Sep 17 00:00:00 2001
From: Blue <OneBlue@users.noreply.github.com>
Date: Mon, 23 Jun 2025 16:24:10 -0700
Subject: [PATCH] Don't display a warning when the binfmt process doesn't have
 a controlling terminal (#13176)

---
 src/linux/init/binfmt.cpp  |  9 ++++++++-
 test/windows/UnitTests.cpp | 11 +++++++++++
 2 files changed, 19 insertions(+), 1 deletion(-)

diff --git a/src/linux/init/binfmt.cpp b/src/linux/init/binfmt.cpp
index d4c6868..e32ebfc 100644
--- a/src/linux/init/binfmt.cpp
+++ b/src/linux/init/binfmt.cpp
@@ -678,12 +678,19 @@ Return Value:
 
     //
     // Ensure that stdin represents the foreground process group.
+    // N.B. It's possible that standard file descriptors point to tty while the process
+    // has no controlling terminal (in case its parent called setsid() without opening a new terminal for instance).
+    // See https://github.com/microsoft/WSL/issues/13173.
     //
 
     auto processGroup = tcgetpgrp(0);
     if (processGroup < 0)
     {
-        LOG_STDERR("tcgetpgrp failed");
+        if (errno != ENOTTY)
+        {
+            LOG_STDERR("tcgetpgrp failed");
+        }
+
         return;
     }
 
diff --git a/test/windows/UnitTests.cpp b/test/windows/UnitTests.cpp
index 8a12a25..228baa5 100644
--- a/test/windows/UnitTests.cpp
+++ b/test/windows/UnitTests.cpp
@@ -6119,5 +6119,16 @@ Error code: Wsl/InstallDistro/WSL_E_INVALID_JSON\r\n",
         VERIFY_ARE_EQUAL(err, L"");
     }
 
+    // Validate that calling the binfmt interpreter with tty fd's but not controlling terminal doesn't display a warning.
+    // See https://github.com/microsoft/WSL/issues/13173.
+    TEST_METHOD(SetSidNoWarning)
+    {
+        auto [out, err] =
+            LxsstuLaunchWslAndCaptureOutput(L"socat - 'EXEC:setsid --wait cmd.exe /c echo OK',pty,setsid,ctty,stderr");
+
+        VERIFY_ARE_EQUAL(out, L"OK\r\r\n");
+        VERIFY_ARE_EQUAL(err, L"");
+    }
+
 }; // namespace UnitTests
 } // namespace UnitTests