Relinquish root privs after securing tcp listener.

diff --git a/burrower.scm b/burrower.scm
index 9db8599..feb26cc 100644 (file)
--- a/burrower.scm
+++ b/burrower.scm
@@ -15,12 +15,11 @@
         (chicken condition)
         (chicken process)
         (chicken process-context)
+        (chicken process-context posix)
         srfi-1 srfi-13 matchable)
 
 ;;; Global constants
 
-(define gopher-index-filename "index")
-
 (define burrower-version "1.0.0")
 
 (define burrower-footer
@@ -29,6 +28,8 @@
         "This gopher hole was dug using Burrower v" burrower-version ".\n"
         "Powered by Chicken Scheme!"))
 
+(define gopher-index-filename "index")
+
 ;;; Server loop
 
 ;; We don't yet use worker threads here to handle requests,
@@ -36,37 +37,48 @@
 ;; While we should fix this, it's actually probably okay, as
 ;; we genuinely don't expect a huge flood of gopher traffic. :-(
 
-(define-record config root-dir host port display-footer)
+(define-record config
+  root-dir host port display-footer user group)
 
 (define (run-server config)
   (set-buffering-mode! (current-output-port) #:line)
-  (print "Gopher server listening on port " (config-port config) " ...")
   (let ((listener (tcp-listen (config-port config))))
-    (let server-loop ()
-      (let-values (((in-port out-port) (tcp-accept listener)))
-        (let* ((line (read-line in-port))
-               (selector (string-trim-both line)))
-          (let-values (((local-ip remote-ip) (tcp-addresses in-port)))
-            (print "Accepted connection from " remote-ip
-                   " on " (seconds->string))
-            (condition-case
-                (begin
-                  (with-output-to-port out-port
-                    (lambda ()
-                      (serve-selector (if (= (string-length selector) 0)
-                                          "/"
-                                          selector)
-                                      config)))
-                  (print "... served selector '" selector "'. Closing connection."))
-              (o (exn)
-                 (print-error-message o out-port)
-                 (print-error-message o)
-                 (print "Error while attempting to serve selector " selector ".")))))
-        (close-input-port in-port)
-        (close-output-port out-port))
-      (server-loop))
-    (tcp-close listener)))
-
+    (print "Gopher server listening on port " (config-port config) " ...")
+    (drop-privs config)
+    (server-loop listener config))
+  (tcp-close listener))
+
+(define (drop-privs config)
+  (let ((uid (config-user config))
+        (gid (config-group config)))
+    (if (not (null? gid)) ; Group first, since only root can switch groups.
+        (set! (current-group-id) gid))
+    (if (not (null? uid))
+        (set! (current-user-id) uid))))
+
+(define (server-loop listener config)
+  (let-values (((in-port out-port) (tcp-accept listener)))
+    (let* ((line (read-line in-port))
+           (selector (string-trim-both line)))
+      (let-values (((local-ip remote-ip) (tcp-addresses in-port)))
+        (print "Accepted connection from " remote-ip
+               " on " (seconds->string))
+        (condition-case
+            (begin
+              (with-output-to-port out-port
+                (lambda ()
+                  (serve-selector (if (= (string-length selector) 0)
+                                      "/"
+                                      selector)
+                                  config)))
+              (print "... served selector '" selector "'. Closing connection."))
+          (o (exn)
+             (print-error-message o out-port)
+             (print-error-message o)
+             (print "Error while attempting to serve selector " selector ".")))))
+    (close-input-port in-port)
+    (close-output-port out-port))
+  (server-loop listener config))
 
 ;;; Selector type inference
 
@@ -301,38 +313,49 @@
 (define (print-usage progname)
   (print "Usage:\n"
          progname " -h/--help\n"
-         progname " [-n/--no-footer] gopher-root-dir server-hostname [server-port]\n"
+         progname " [-n/--no-footer] [-u/--user UID] [-g/--group GID] root-dir hostname [port]\n"
          "\n"
-         "The -n option tells the server to not display a directory footer."))
+         "The -n option tells the server to not display a directory footer."
+         "The -u and -g can be used to set the UID and GID of the process following"
+         "the creation of the TCP port listener (which often requires root)."))
 
 (define (main)
   (let* ((progname (car (argv)))
-         (args (cdr (argv)))
-         (config (make-config '() '() 70 #t)))
-
-    (if (or (null? args)
-            (equal? (car args) "-h")
-            (equal? (car args) "--help"))
+         (config (make-config '() '() 70 #t '() '())))
+    (if (null? (cdr (argv)))
         (print-usage progname)
-        (begin
-          (if (or (equal? (car args) "-n")
-                  (equal? (car args) "--no-footer"))
-              (begin
-                (config-display-footer-set! config #f)
-                (set! args (cdr args))))
-          (if (or (< (length args) 2)
-                  (> (length args) 3))
-              (print-usage progname)
-              (begin
-                (config-root-dir-set! config (car args))
-                (config-host-set! config (cadr args))
-                (if (= (length args) 3)
-                    (config-port-set! config (string->number (caddr args))))
-                (run-server config)))))))
+        (let loop ((args (cdr (argv))))
+          (let ((this-arg (car args))
+                (rest-args (cdr args)))
+            (if (string-prefix? "-" this-arg)
+                (cond
+                 ((or (equal? this-arg "-h")
+                      (equal? this-arg "--help"))
+                  (print-usage progname))
+                 ((or (equal? this-arg "-n")
+                      (equal? this-arg "--no-footer"))
+                  (config-display-footer-set! config #f)
+                  (loop rest-args))
+                 ((or (equal? this-arg "-u")
+                      (equal? this-arg "--user"))
+                  (config-user-set! config (string->number (car rest-args)))
+                  (loop (cdr rest-args)))
+                 ((or (equal? this-arg "-g")
+                      (equal? this-arg "--group"))
+                  (config-group-set! config (string->number (car rest-args)))
+                  (loop (cdr rest-args)))
+                 (else
+                  (print-usage progname)))
+                (begin
+                  (config-root-dir-set! config (car args))
+                  (config-host-set! config (cadr args))
+                  (if (>= (length rest-args) 2)
+                      (config-port-set! config (string->number (caddr args))))
+                  (run-server config))))))))
 
 (main)
 
 ;; (define (test)
-;;   (run-server (make-config "gopher-root" "localhost" 70 #t)))
+;;   (run-server (make-config "gopher-root" "localhost" 70 #t '() '())))
 
 ;; (test)