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.

1 files changed, 29 insertions, 2 deletions

diff --git a/cgi.c b/cgi.c
index abf3e5ee..e7ac8c4b 100644
--- a/cgi.c
+++ b/cgi.c
@@ -1,4 +1,4 @@
-/*	$Id: cgi.c,v 1.75 2014/07/18 19:03:39 schwarze Exp $ */
+/*	$Id: cgi.c,v 1.76 2014/07/19 11:35:12 schwarze Exp $ */
 /*
  * Copyright (c) 2011, 2012 Kristaps Dzonsons <kristaps@bsd.lv>
  * Copyright (c) 2014 Ingo Schwarze <schwarze@usta.de>
@@ -466,6 +466,17 @@ 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)
 {
@@ -523,6 +534,15 @@ 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
@@ -777,7 +797,8 @@ 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)
@@ -810,6 +831,12 @@ 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);