From 8147578414af9663e24289e895fc689a48a1de06 Mon Sep 17 00:00:00 2001
From: schwarze <schwarze@openbsd.org>
Date: Sat, 19 Jul 2014 11:35:09 +0000
Subject: [PATCH] Security fix: Validate the name of the file to show before
 opening it. Only allow relative filenames starting with "man" or "cat" and
 containing neither "/.." nor "../".

While here, correct the condition discarding an initial "./".

Vulnerability found by Sebastien Marie <semarie-openbsd at latrappe dot fr>.
Many thanks for sending a patch; however, i did not use it but made the
checks even stricter.
---
 usr.bin/mandoc/cgi.c | 31 +++++++++++++++++++++++++++++--
 1 file changed, 29 insertions(+), 2 deletions(-)

diff --git a/usr.bin/mandoc/cgi.c b/usr.bin/mandoc/cgi.c
index bfe8b605c0a..bf175c8e4b9 100644
--- a/usr.bin/mandoc/cgi.c
+++ b/usr.bin/mandoc/cgi.c
@@ -1,4 +1,4 @@
-/*	$Id: cgi.c,v 1.15 2014/07/18 19:02:07 schwarze Exp $ */
+/*	$Id: cgi.c,v 1.16 2014/07/19 11:35:09 schwarze Exp $ */
 /*
  * Copyright (c) 2011, 2012 Kristaps Dzonsons <kristaps@bsd.lv>
  * Copyright (c) 2014 Ingo Schwarze <schwarze@usta.de>
@@ -462,6 +462,17 @@ resp_searchform(const struct req *req)
 	puts("<!-- End search form. //-->");
 }
 
+static int
+validate_filename(const char *file)
+{
+
+	if ('.' == file[0] && '/' == file[1])
+		file += 2;
+
+	return ( ! (strstr(file, "../") || strstr(file, "/..") ||
+	    (strncmp(file, "man", 3) && strncmp(file, "cat", 3))));
+}
+
 static void
 pg_index(const struct req *req)
 {
@@ -519,6 +530,15 @@ pg_searchres(const struct req *req, struct manpage *r, size_t sz)
 	int		 prio, priouse;
 	char		 sec;
 
+	for (i = 0; i < sz; i++) {
+		if (validate_filename(r[i].file))
+			continue;
+		fprintf(stderr, "invalid filename %s in %s database\n",
+		    r[i].file, req->q.manpath);
+		pg_error_internal();
+		return;
+	}
+
 	if (1 == sz) {
 		/*
 		 * If we have just one result, then jump there now
@@ -773,7 +793,8 @@ format(const struct req *req, const char *file)
 static void
 resp_show(const struct req *req, const char *file)
 {
-	if ('.' == file[0] || '/' == file[1])
+
+	if ('.' == file[0] && '/' == file[1])
 		file += 2;
 
 	if ('c' == *file)
@@ -806,6 +827,12 @@ pg_show(const struct req *req, const char *path)
 		return;
 	}
 
+	if ( ! validate_filename(sub)) {
+		pg_error_badrequest(
+		    "You specified an invalid manual file.");
+		return;
+	}
+
 	resp_begin_html(200, NULL);
 	resp_searchform(req);
 	resp_show(req, sub);
-- 
2.20.1