rack: add option to drop privileges

3 files changed, 33 insertions, 0 deletions

diff --git a/examples/rack-example-config.rb b/examples/rack-example-config.rb
index d8d3dcb..8f5e1f1 100644
--- a/examples/rack-example-config.rb
+++ b/examples/rack-example-config.rb
@@ -4,6 +4,9 @@ server_push true
 threaded false # create a new thread per request
 fallback_legacy "127.0.0.1:8080" # forward if client doesn't support HTTP/2
 
+user "nobody"
+group "nobody"
+
 # listeners may be multiple
 listener :unix, { path: "/tmp/plum.sock", mode: 600 }
 listener :tcp, { hostname: "0.0.0.0", port: 80 }
diff --git a/lib/plum/rack/dsl.rb b/lib/plum/rack/dsl.rb
index b1f8bb0..006d6dc 100644
--- a/lib/plum/rack/dsl.rb
+++ b/lib/plum/rack/dsl.rb
@@ -49,6 +49,14 @@ module Plum
           @config[:fallback_legacy_host] = h
           @config[:fallback_legacy_port] = p.to_i
         end
+
+        def user(username)
+          @config[:user] = username
+        end
+
+        def group(groupname)
+          @config[:group] = groupname
+        end
       end
     end
   end
diff --git a/lib/plum/rack/server.rb b/lib/plum/rack/server.rb
index 1f3d32c..9a0caf4 100644
--- a/lib/plum/rack/server.rb
+++ b/lib/plum/rack/server.rb
@@ -17,6 +17,10 @@ module Plum
 
         @logger.info("Plum #{::Plum::VERSION}")
         @logger.info("Config: #{config}")
+
+        if @config[:user]
+          drop_privileges
+        end
       end
 
       def start
@@ -100,6 +104,24 @@ module Plum
       ensure
         upstream.close if upstream
       end
+
+      def drop_privileges
+        begin
+          user = @config[:user]
+          group = @config[:group] || user
+          @logger.info "Dropping process privilege to #{user}:#{group}"
+
+          cuid, cgid = Process.euid, Process.egid
+          tuid, tgid = Etc.getpwnam(user).uid, Etc.getgrnam(group).gid
+
+          Process.initgroups(user, tgid)
+          Process::GID.change_privilege(tgid)
+          Process::UID.change_privilege(tuid)
+        rescue Errno::EPERM => e
+          @ogger.fatal "Could not change privilege: #{e}"
+          exit 2
+        end
+      end
     end
   end
 end