From a10ba5e47422e649c22a509646a8d76e8be1e5b5 Mon Sep 17 00:00:00 2001
From: Andrew McCabe <amccabe@users.noreply.github.com>
Date: Tue, 29 Sep 2026 03:58:31 -0400
Subject: [PATCH] pkg/pidhandle: handle ESRCH from openByHandleAt

The kernel can return ESRCH in addition to ESTALE from open_by_handle_at
when the process no longer exists.

Signed-off-by: Andrew McCabe <amccabe@users.noreply.github.com>
---
 pkg/pidhandle/pidhandle_linux.go      |  4 +++-
 pkg/pidhandle/pidhandle_linux_test.go | 26 ++++++++++++++++++++++++++
 2 files changed, 29 insertions(+), 1 deletion(-)

diff --git a/pkg/pidhandle/pidhandle_linux.go b/pkg/pidhandle/pidhandle_linux.go
index c9e0b6deda..1e3cddfde5 100644
--- a/pkg/pidhandle/pidhandle_linux.go
+++ b/pkg/pidhandle/pidhandle_linux.go
@@ -127,7 +127,9 @@ func NewPIDHandleFromString(pid int, pidData string) (PIDHandle, error) {
 		defer unix.Close(fd)
 		pidfd, err := openByHandleAt(fd, fh, unix.O_CLOEXEC)
 		if err != nil {
-			if errors.Is(err, unix.ESTALE) {
+			// The process is gone: ESTALE once it has been reaped, ESRCH
+			// while it is being reaped (pidfs_export_open).
+			if errors.Is(err, unix.ESTALE) || errors.Is(err, unix.ESRCH) {
 				h.normalHandle.pidData = noSuchProcessID
 				return &h, nil
 			}
diff --git a/pkg/pidhandle/pidhandle_linux_test.go b/pkg/pidhandle/pidhandle_linux_test.go
index 7ddcbcc1aa..b15a3c1915 100644
--- a/pkg/pidhandle/pidhandle_linux_test.go
+++ b/pkg/pidhandle/pidhandle_linux_test.go
@@ -7,6 +7,7 @@ import (
 	"testing"
 
 	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
 	"golang.org/x/sys/unix"
 )
 
@@ -151,6 +152,31 @@ func TestNewPIDHandleFromStringWrongPidData(t *testing.T) {
 	}
 }
 
+func TestNewPIDHandleFromStringProcessGone(t *testing.T) {
+	// openByHandleAt may report a process that no longer exists with either
+	// ESTALE or ESRCH; either must leave a handle to a dead process.
+	for _, openErr := range []error{unix.ESTALE, unix.ESRCH} {
+		t.Run(openErr.Error(), func(t *testing.T) {
+			original_openByHandleAt := openByHandleAt
+			t.Cleanup(func() {
+				openByHandleAt = original_openByHandleAt
+			})
+			openByHandleAt = func(_ int, _ unix.FileHandle, _ int) (fd int, err error) {
+				return -1, openErr
+			}
+
+			h, err := NewPIDHandleFromString(os.Getpid(), nameToHandlePrefix+"254 74657374")
+			require.NoError(t, err)
+			defer h.Close()
+
+			alive, err := h.IsAlive()
+			assert.NoError(t, err)
+			assert.False(t, alive)
+			assert.ErrorIs(t, h.Kill(unix.SIGTERM), unix.ESRCH)
+		})
+	}
+}
+
 func TestPIDHandlePidfdStartTime(t *testing.T) {
 	h, err := NewPIDHandleFromString(os.Getpid(), "start-time:1234567890")
 	assert.NoError(t, err)