cmd/go: reject toolchain directives containing path separators
If GOTOOLCHAIN="path" or "auto", the go command uses exec.LookPath to
search for it in order to allow toolchains to refer to local-only
toolchain variants (such as toolchains built from enterprise- or
distro-patched source). However, those toolchains should only be
resolved from $PATH, not relative to the working directory of the
command.
Thanks to Juho Nurminen of Mattermost for reporting this issue.
Fixes #62198.
Fixes CVE-2023-39320.
Change-Id: I247c7acea95d737362dd0475e9fc8515430d0fcc
Reviewed-on: https://team-review.git.corp.google.com/c/golang/go-private/+/
1996318
Run-TryBot: Roland Shoemaker <bracewell@google.com>
Reviewed-by: Damien Neil <dneil@google.com>
Reviewed-by: Roland Shoemaker <bracewell@google.com>
Reviewed-on: https://go-review.googlesource.com/c/go/+/526158
Reviewed-by: Bryan Mills <bcmills@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>