os: UserConfigDir and UserCacheDir should disallow relative paths in the environment variables

[rhysd]

Go version

go version go1.22.5 linux/amd64

Output of go env in your module/workspace:

GO111MODULE=''
GOARCH='amd64'
GOBIN=''
GOCACHE='/home/rhysd/.cache/go-build'
GOENV='/home/rhysd/.config/go/env'
GOEXE=''
GOEXPERIMENT=''
GOFLAGS=''
GOHOSTARCH='amd64'
GOHOSTOS='linux'
GOINSECURE=''
GOMODCACHE='/home/rhysd/go/pkg/mod'
GONOPROXY=''
GONOSUMDB=''
GOOS='linux'
GOPATH='/home/rhysd/go'
GOPRIVATE=''
GOPROXY='https://proxy.golang.org,direct'
GOROOT='/snap/go/10660'
GOSUMDB='sum.golang.org'
GOTMPDIR=''
GOTOOLCHAIN='auto'
GOTOOLDIR='/snap/go/10660/pkg/tool/linux_amd64'
GOVCS=''
GOVERSION='go1.22.5'
GCCGO='gccgo'
GOAMD64='v1'
AR='ar'
CC='gcc'
CXX='g++'
CGO_ENABLED='1'
GOMOD='/dev/null'
GOWORK=''
CGO_CFLAGS='-O2 -g'
CGO_CPPFLAGS=''
CGO_CXXFLAGS='-O2 -g'
CGO_FFLAGS='-O2 -g'
CGO_LDFLAGS='-O2 -g'
PKG_CONFIG='pkg-config'
GOGCCFLAGS='-fPIC -m64 -pthread -Wl,--no-gc-sections -fmessage-length=0 -ffile-prefix-map=/tmp/go-build2010600332=/tmp/go-build -gno-record-gcc-switches'

What did you do?

Run the following code by go run.

package main

import "os"

func main() {
	os.Setenv("XDG_CONFIG_HOME", "hello")
	d, err := os.UserConfigDir()
	if err == nil {
		panic("unexpectedly successeded: " + d)
	}
}

And run the following code too.

package main

import "os"

func main() {
	os.Setenv("XDG_CACHE_HOME", "hello")
	d, err := os.UserCacheDir()
	if err == nil {
		panic("unexpectedly successeded: " + d)
	}
}

What did you see happen?

Both codes panicked:

panic: unexpectedly successeded: hello

goroutine 1 [running]:
main.main()
	/home/rhysd/Downloads/test.go:9 +0x68
exit status 2

What did you expect to see?

Both codes should not panic.

os.UserConfigDir and os.UserCacheDir should return errors when the corresponding XDG environment variables contain relative paths.

The documens are saying that

On Unix systems, it returns $XDG_CONFIG_HOME as specified by https://specifications.freedesktop.org/basedir-spec/basedir-spec-latest.html if non-empty

However, XDG Base Directory Specification is saying that

All paths set in these environment variables must be absolute. If an implementation encounters a relative path in any of these variables it should consider the path invalid and ignore it.

So os.UserConfigDir and os.UserCacheDir don't conform the specification.

[rhysd]

I'll try to make a patch for fixing this issue.

[gabyhelp]

Related Issues and Documentation

• affected/package: os #57472 (closed)
• cmd/compile, os: Go code in shared library under Android can't read env variables #59843
• os: TestUserConfigDir and TestUserCacheDir expect writable $HOME on linux #64990 (closed)
• cmd/go: error for unset $GOPATH when GOROOT is $HOME/go is unhelpful #34628
• os: new runtime.GOOS of "ios" breaks os.User*Dir functions on GoTip for Go1.16 #42878 (closed)
• cmd/go: `go build` (etc.) doesn't work with symlinks when invoked via os/exec.Command with mismatched PWD #63644 (closed)
• cmd/go: can only run "go env" in certain places #35409 (closed)
• x/tools/go/packages: relative "files=" query path are not relative to Config.Dir #65965
• cmd/go: /root/go as GOROOT results in "missing $GOPATH" #34488 (closed)
• cmd/go: emits warning when GOPATH == GOROOT #65656 (closed)

_{(Emoji vote if this was helpful or unhelpful; more detailed feedback welcome in this discussion.)}

[gopherbot]

Change https://go.dev/cl/598655 mentions this issue: os: check relative paths in UserConfigDir and UserCacheDir