filesystemCollector crash with non-utf8 mount point

[PierreF]

node_export crash when a filesystem is mounted on a non-utf8 path. This is possible on Linux, because on Linux IIRC path are binary (with most of the time being UTF-8). But if someone using different encoding for paths, you could ends with non-utf8 paths which result in a node_exporter crash:

panic: label value "/mnt/cass\xe9" is not valid UTF-8

goroutine 35 [running]:
github.com/prometheus/client_golang/prometheus.MustNewConstMetric(...)
        /go/pkg/mod/github.com/prometheus/client_golang@v1.23.2/prometheus/value.go:129
github.com/prometheus/node_exporter/collector.(*filesystemCollector).Update(0x400019e9a0, 0x40002463f0)
        /app/collector/filesystem_common.go:198 +0x704
github.com/prometheus/node_exporter/collector.execute({0x7f8189, 0xa}, {0x92ebe0, 0x400019e9a0}, 0x40002463f0, 0x4000174f50)
        /app/collector/collector.go:160 +0x60
github.com/prometheus/node_exporter/collector.NodeCollector.Collect.func1({0x7f8189?, 0x0?}, {0x92ebe0?, 0x400019e9a0?})
        /app/collector/collector.go:151 +0x34
created by github.com/prometheus/node_exporter/collector.NodeCollector.Collect in goroutine 33
        /app/collector/collector.go:150 +0xa4

Reproduce

On Linux (tested on a Ubuntu 24.04 arm64 VM, but shouldn't matter):

• Mount a filesystem on a utf-8 invalid path (this might required bash as shell, I'm unsure if $'\xe9' is portable)

fallocate -l 32m /root/disk.dd
mkfs -t ext2 /root/disk.dd
mount --mkdir /root/disk.dd /mnt/cass$'\xe9'

• Run node_exporter

./node_exporter

• Do a collection

curl http://localhost:9100/metrics

To cleanup:

umount /mnt/cass$'\xe9'
rm /root/disk.dd

Version information

# ./node_exporter --version
node_exporter, version 1.10.2 (branch: HEAD, revision: 654f19dee6a0c41de78a8d6d870e8c742cdb43b9)
  build user:       root@b29b4019149a
  build date:       20251025-20:06:08
  go version:       go1.25.3
  platform:         linux/arm64
  tags:             unknown

# lsb_release -a
No LSB modules are available.
Distributor ID: Ubuntu
Description:    Ubuntu 24.04.1 LTS
Release:        24.04
Codename:       noble

# uname -a
Linux ubuntu2404 6.8.0-51-generic #52-Ubuntu SMP PREEMPT_DYNAMIC Thu Dec  5 13:32:09 UTC 2024 aarch64 aarch64 aarch64 GNU/Linux