security improvements, switched to single session db file

2 files changed, 68 insertions, 34 deletions

diff --git a/doc/security.mdwn b/doc/security.mdwn
index 9c867f42f..e34dc5ed4 100644
--- a/doc/security.mdwn
+++ b/doc/security.mdwn
@@ -52,10 +52,10 @@ attacker couldn't get ikiwiki to svn up while another instance was running.
 
 If multiple people can write to the source directory ikiwiki is using, then
 one can cause trouble for the other when they run ikiwiki through symlink
-sttacks.
+attacks.
 
 So it's best if only one person can ever write to the checkout that ikiwiki
-compiles the moo from.
+compiles the wiki from.
 
 ## webserver symlink attacks
 
@@ -63,34 +63,11 @@ If someone checks in a symlink to /etc/passwd, ikiwiki would publish that.
 To aoid this, ikiwiki will need to avoid reading files that are symlinks.
 TODO and note discussion of races above.
 
-## cgi data security
-
-When ikiwiki runs as a cgi to edit a page, it is passed the name of the
-page to edit. It has to make sure to sanitise this page, to prevent eg,
-editing of ../../../foo, or editing of files that are not part of the wiki,
-such as subversion dotfiles. This is done by sanitising the filename
-removing unallowed characters, then making sure it doesn't start with "/"
-or contain ".." or "/.svn/". Annoyingly ad-hoc, this kind of code is where
-security holes breed. It needs a test suite at the very least.
-
-## cgi password security
-
-Login to the wiki involves sending a password in cleartext over the net.
-Cracking the password only allows editing the moo as that user though.
-If you care, you can use https, I suppose.
-
-## CGI::Session security
-
-Is CGI::Session secure? Well, it writes the session files world-readable,
-which could be used by a local attacker to take over someone's session.
-
-I have no idea if CGI::Session writes session files securely to /tmp.
-ikiwiki makes it write them to a directory it controls (but see "multiple
-accessors of wiki source directory" above).
-
 ----
 
-# Probable non-holes
+# Hopefully non-holes
+
+(AKA, the assumptions that will be the root of most security holes...)
 
 ## exploting ikiwiki with bad content
 
@@ -100,8 +77,9 @@ Note that ikiwiki runs with perl taint checks on, so this is unlikely.
 ## publishing cgi scripts
 
 ikiwiki does not allow cgi scripts to be published as part of the wiki. Or
-rather, the script is published, but it's not marked executable, so
-hopefully your web server will not run it.
+rather, the script is published, but it's not marked executable (except in
+the case of "destination directory file replacement" below), so hopefully
+your web server will not run it.
 
 ## suid wrappers
 
@@ -111,8 +89,48 @@ for example to be used in a [[post-commit]] hook by people who cannot write
 to the html pages, etc.
 
 If the wrapper script is made suid, then any bugs in this wrapper would be
-security holes. The wrapper is written as securely as I know how, is based on code that has a history of security use long before ikiwiki, and there's been no problem yet.
+security holes. The wrapper is written as securely as I know how, is based
+on code that has a history of security use long before ikiwiki, and there's
+been no problem yet.
 
 ## shell exploits
 
-ikiwiki does not expose untrusted data to the shell. In fact it doesn't use system() at all, and the only use of backticks is on data supplied by the wiki admin. And it runs with taint checks on of course..
+ikiwiki does not expose untrusted data to the shell. In fact it doesn't use
+system() at all, and the only use of backticks is on data supplied by the
+wiki admin. And it runs with taint checks on of course..
+
+## destination directory file replacement
+
+Any file in the destination directory that is a valid page filename can be
+replaced, even if it was not originally rendered from a page. For example,
+ikiwiki.cgi could be edited in the wiki, and it would write out a
+replacement. File permission is preseved. Yipes!
+
+This was fixed by making ikiwiki check if the file it's writing to exists;
+if it does then it has to be a file that it's aware of creating before, or
+it will refuse to create it.
+
+Still, this sort of attack is something to keep in mind.
+
+## cgi data security
+
+When ikiwiki runs as a cgi to edit a page, it is passed the name of the
+page to edit. It has to make sure to sanitise this page, to prevent eg,
+editing of ../../../foo, or editing of files that are not part of the wiki,
+such as subversion dotfiles. This is done by sanitising the filename
+removing unallowed characters, then making sure it doesn't start with "/"
+or contain ".." or "/.svn/". Annoyingly ad-hoc, this kind of code is where
+security holes breed. It needs a test suite at the very least.
+
+## cgi password security
+
+Login to the wiki involves sending a password in cleartext over the net.
+Cracking the password only allows editing the moo as that user though.
+If you care, you can use https, I suppose.
+
+## CGI::Session security
+
+I've audited this module and it is massively insecure by default. ikiwiki
+uses it in one of the few secure ways; by forcing it to write to a
+directory it controls (and not /tmp) and by setting a umask that makes the
+file not be world readable.
diff --git a/ikiwiki b/ikiwiki
index 058b3ffa2..cb43f6b0b 100755
--- a/ikiwiki
+++ b/ikiwiki
@@ -306,6 +306,17 @@ sub finalize ($$) { #{{{
 	return $template->output;
 } #}}}
 
+# Important security check. Make sure to call this before saving any files
+# to the source directory.
+sub check_overwrite ($$) { #{{{
+	my $dest=shift;
+	my $src=shift;
+	
+	if (! exists $renderedfiles{$src} && -e $dest) {
+		error("$dest exists and was not rendered from $src before, not overwriting");
+	}
+} #}}}
+		
 sub render ($) { #{{{
 	my $file=shift;
 	
@@ -320,12 +331,14 @@ sub render ($) { #{{{
 		$content=htmlize($type, $content);
 		$content=finalize($content, $page);
 		
+		check_overwrite("$destdir/".htmlpage($page), $page);
 		writefile("$destdir/".htmlpage($page), $content);
 		$oldpagemtime{$page}=time;
 		$renderedfiles{$page}=htmlpage($page);
 	}
 	else {
 		$links{$file}=[];
+		check_overwrite("$destdir/$file", $file);
 		writefile("$destdir/$file", $content);
 		$oldpagemtime{$file}=time;
 		$renderedfiles{$file}=$file;
@@ -941,8 +954,11 @@ sub cgi () { #{{{
 	}
 	
 	CGI::Session->name("ikiwiki_session");
-	my $session = CGI::Session->new(undef, $q,
-		{ Directory=> "$srcdir/.ikiwiki/sessions" });
+
+	my $oldmask=umask(077);
+	my $session = CGI::Session->new("driver:db_file", $q,
+		{ FileName => "$srcdir/.ikiwiki/sessions.db" });
+	umask($oldmask);
 	
 	# Everything below this point needs the user to be signed in.
 	if ((! $anonok && ! defined $session->param("name")) || $do eq 'signin') {