teximg: Make TeX handle preventing unsafe things; remove insufficient blacklist

TeX has configuration options that prevent unsafe things like shell
escapes and insecure file reads/writes.  Turn all of them on.

teximg's regex-based blacklist does not suffice.  For instance:

[[!teximg code="""
\catcode`\%=0
%input{/etc/passwd}
"""]]

Remove the blacklist, since the TeX configuration options seal off the
underlying mechanisms more safely, and the blacklist blocks other TeX
commands that can prove useful.

IkiWiki/Plugin/teximg.pm

@@ -69,13 +69,7 @@ sub preprocess (@) {
 	if (! defined $code && ! length $code) {
 		error gettext("missing tex code");
 	}
-
-	if (check($code)) {
-		return create($code, check_height($height), \%params);
-	}
-	else {
-		error gettext("code includes disallowed latex commands")
-	}
+	return create($code, check_height($height), \%params);
 }
 
 sub check_height ($) {
@@ -155,7 +149,7 @@ sub gen_image ($$$$) {
 	my $tmp = eval { create_tmp_dir($digest) };
 	if (! $@ &&
 	    writefile("$digest.tex", $tmp, $tex) &&
-	    system("cd $tmp; latex --interaction=nonstopmode $tmp/$digest.tex > /dev/null") == 0 &&
+	    system("cd $tmp; shell_escape=f openout_any=p openin_any=p latex --interaction=nonstopmode $digest.tex < /dev/null > /dev/null") == 0 &&
 	    # ensure destination directory exists
 	    writefile("$imagedir/$digest.png", $config{destdir}, "") &&
 	    (($config{teximg_dvipng} &&
@@ -191,34 +185,4 @@ sub create_tmp_dir ($) {
 	return $tmpdir;
 }
 
-sub check ($) {
-	# Check if the code is ok
-	my $code = shift;
-
-	my @badthings = (
-		qr/\$\$/,
-		qr/\\include/,
-		qr/\\includegraphic/,
-		qr/\\usepackage/,
-		qr/\\newcommand/, 
-		qr/\\renewcommand/,
-		qr/\\def/,
-		qr/\\input/,
-		qr/\\open/,
-		qr/\\loop/,
-		qr/\\errorstopmode/,
-		qr/\\scrollmode/,
-		qr/\\batchmode/,
-		qr/\\read/,
-		qr/\\write/,
-	);
-	
-	foreach my $thing (@badthings) {
-		if ($code =~ m/$thing/ ) {
-			return 0;
-		}
-	}
-	return 1;
-}
-
 1

debian/changelog

@@ -1,5 +1,6 @@
 ikiwiki (3.1415926) UNRELEASED; urgency=low
 
+  [ Joey Hess ]
   * po: Detect if nowrapi18n can't be passed to po4a, and warn about
     the old version, but continue. Closes: #541205 
   * inline: Avoid use of my $_ as it fails with older perls.
@@ -40,6 +41,10 @@ ikiwiki (3.1415926) UNRELEASED; urgency=low
   * img: Don't generate new verison of image if it is scaled to be
     larger in either dimension.
 
+  [ Josh Triplett ]
+  * teximg: Replace the insufficient blacklist with the built-in security
+    mechanisms of TeX.
+
  -- Joey Hess <joeyh@debian.org>  Wed, 12 Aug 2009 12:25:30 -0400
 
 ikiwiki (3.141592) unstable; urgency=low