From d3b04e56003682a927182d049f6a68ceaa2e9d93 Mon Sep 17 00:00:00 2001
From: Dan Fandrich <dan@coneharvesters.com>
Date: Mon, 4 May 2026 20:48:52 -0700
Subject: [PATCH] tests: add an assert to avoid IPC blocking

If so much data is being sent over the internal IPC pipe that the pipe
buffer fills and the syscall blocks, the program will hang. Add an
assert to ensure that this limit is never reached. The buffer size is
going to be different on different platforms, so choose 1KB which is
likely to be a reasonable lower bound on just about any system.
Currently, the maximum amount ever written is <100 bytes, so this should
provide plenty of headroom.

Spotted by Codex Security

Closes #21688
---
 tests/runner.pm | 1 +
 1 file changed, 1 insertion(+)

diff --git a/tests/runner.pm b/tests/runner.pm
index a398800946..72cca945e1 100644
--- a/tests/runner.pm
+++ b/tests/runner.pm
@@ -1336,6 +1336,7 @@ sub controlleripccall {
     my $margs = freeze \@_;
 
     # Send IPC call via pipe
+    length($margs) < 1000 || die "A large IPC write risks blocking on some platforms";
     my $err;
     while(! defined ($err = syswrite($controllerw{$runnerid}, (pack "L", length($margs)) . $margs)) || $err <= 0) {
         if((!defined $err && ! $!{EINTR}) || (defined $err && $err == 0)) {