[BUG] panic: runtime error: slice bounds out of range [:-1] - segfault when using ingress controller

[MrBlaise]

I am using haproxy ingress controller and I observed that during heavy load when the backend pods are restarted haproxy can sometime fail with a segmentation fault. Based on the stacktrace, the it roots from the client-native library, specifically this line: https://github.com/haproxytech/client-native/blob/master/runtime/runtime_client.go#L165

Stacktrace:

[NOTICE]   (69) : haproxy version is 3.1.0-f2b9791
[ALERT]    (69) : Current worker (4635) exited with code 139 (Segmentation fault)
[WARNING]  (69) : A worker process unexpectedly died and this can only be explained by a bug in haproxy or its dependencies.
Please check that you are running an up to date and maintained version of haproxy and open a bug report.
[ALERT]    (69) : exit-on-failure: killing every processes with SIGTERM
HAProxy version 3.1.0-f2b9791 2024/11/26 - https://haproxy.org/
Status: stable branch - will stop receiving fixes around Q1 2026.
Known bugs: http://www.haproxy.org/bugs/bugs-3.1.0.html
Running on: Linux 6.1.0-27-amd64 #1 SMP PREEMPT_DYNAMIC Debian 6.1.115-1 (2024-11-01) x86_64
[WARNING]  (69) : Former worker (4615) exited with code 143 (Terminated)
[WARNING]  (69) : All workers exited. Exiting... (139)
panic: runtime error: slice bounds out of range [:-1]

goroutine 444 [running]:
github.com/haproxytech/client-native/v5/runtime.(*client).Reload(0x14?)
	/go/pkg/mod/github.com/haproxytech/client-native/[email protected]/runtime/runtime_client.go:166 +0x2ba
github.com/haproxytech/kubernetes-ingress/pkg/haproxy/process.(*s6Control).Service(0xc001dec008, {0x263f416?, 0x8?})
	/src/pkg/haproxy/process/s6-overlay.go:61 +0xd5
github.com/haproxytech/kubernetes-ingress/pkg/controller.(*HAProxyController).updateHAProxy(0xc000de7808)
	/src/pkg/controller/controller.go:204 +0xa58
github.com/haproxytech/kubernetes-ingress/pkg/controller.(*HAProxyController).SyncData(0xc000de7808)
	/src/pkg/controller/monitor.go:38 +0x5b2
github.com/haproxytech/kubernetes-ingress/pkg/controller.(*HAProxyController).Start(0xc000de7808)
	/src/pkg/controller/controller.go:100 +0x209
created by main.main in goroutine 1
	/src/main.go:164 +0xe65
Ingress Controller exited with fatal code 2, taking down the S6 supervision tree

https://github.com/haproxytech/client-native/blob/master/runtime/runtime_client.go#L165

	output, err := c.runtime.ExecuteMaster("reload")
	if err != nil {
		return "", fmt.Errorf("cannot reload: %w", err)
	}
	parts := strings.SplitN(output, "\n--\n", 2)
	if len(parts) == 1 {
		// No startup logs. This happens when HAProxy is compiled without USE_SHM_OPEN.
		status = output[:len(output)-1]
	} else {
		status, logs = parts[0], parts[1]
	}

I believe the root cause here is that output is never checked whether it is empty, and thus, this status = output[:len(output)-1] can become this status = output[:-1], causing the panic.