doctor/permissions: add new check to print process permissions

Since users can run tailscaled in a variety of ways (root, non-root,
non-root with process capabilities on Linux), this check will print the
current process permissions to the log to aid in debugging.

Signed-off-by: Andrew Dunham <andrew@du.nham.ca>
Change-Id: Ida93a206123f98271a0c664775d0baba98b330c7

doctor/permissions/permissions_bsd.go

@@ -0,0 +1,23 @@
+// Copyright (c) Tailscale Inc & AUTHORS
+// SPDX-License-Identifier: BSD-3-Clause
+
+//go:build darwin || freebsd || openbsd
+
+package permissions
+
+import (
+	"golang.org/x/sys/unix"
+	"tailscale.com/types/logger"
+)
+
+func permissionsImpl(logf logger.Logf) error {
+	groups, _ := unix.Getgroups()
+	logf("uid=%s euid=%s gid=%s egid=%s groups=%s",
+		formatUserID(unix.Getuid()),
+		formatUserID(unix.Geteuid()),
+		formatGroupID(unix.Getgid()),
+		formatGroupID(unix.Getegid()),
+		formatGroups(groups),
+	)
+	return nil
+}