threads / patch / 19441

patchgitweb: Sanitize title attribute in format_subject_html

Subject: [PATCH] gitweb: Sanitize title attribute in format_subject_html

## tl;dr

3 messages between May 22, 2009 and May 22, 2009. Diffs are folded; open one to read it.

replies: 2people: 1as markdown or json

Jakub Narebski· May 22, 2009, 15:35 UTC · lore

Replace control characters with question mark '?' (like in chop_and_esc_str).

A little background: some web browsers turn on strict (and unforgiving) XML validating mode for XHTML documents served using application/xhtml+xml content type. This means among others that control characters are forbidden to appear in gitweb output.

CGI.pm does by default slight escaping (using simple_escape subroutine from CGI::Util) of all _attribute_ values (depending on the value of autoEscape, by default on). This escaping, at least in CGI.pm version 3.10 (most current version at CPAN is 3.43), is minimal: only '"', '&', '<' and '>' are escaped using named HTML entity references (&quot;, &amp;, &lt; and &gt; respectively). But simple_escape does not do escaping of control characters such as ^X which are invalid in XHTML (in strict mode).

If by some accident commit message do contain some control character in first 50 characters (more or less) of first line of commit message, and this line is longer than 50 characters (so gitweb shortens it for display), then gitweb would put this control character in title attribute (and CGI.pm would not remove them). The tag _contents_ is safe because it is escaped using esc_html() explicitly, and it replaces control characters by their printable representation.

While at it: chop_and_escape_str doesn't need capturing group.
Noticed-by: Paul Gortmaker <paul.gortmaker@windriver.com>
Signed-off-by: Jakub Narebski <jnareb@gmail.com>
---
This issue first appeared (with a wrong solution) month ago in
http://thread.gmane.org/gmane.comp.version-control.git/116755
I'm sorry Paul that it took so long to fix it.

This patch will be followed by 'lite' version, with minimal commit message (this one is a bit long), and with failed attempt using esc_attr.

 gitweb/gitweb.perl |    3 ++-
 1 files changed, 2 insertions(+), 1 deletions(-)
Show changes to gitweb/gitweb.perl +2 −1
diff --git a/gitweb/gitweb.perl b/gitweb/gitweb.perl
index 05702e4..1e7e2d8 100755
--- a/gitweb/gitweb.perl
+++ b/gitweb/gitweb.perl
@@ -1236,7 +1236,7 @@ sub chop_and_escape_str {
 	if ($chopped eq $str) {
 		return esc_html($chopped);
 	} else {
-		$str =~ s/([[:cntrl:]])/?/g;
+		$str =~ s/[[:cntrl:]]/?/g;
 		return $cgi->span({-title=>$str}, esc_html($chopped));
 	}
 }
@@ -1459,6 +1459,7 @@ sub format_subject_html {
 	$extra = '' unless defined($extra);
 
 	if (length($short) < length($long)) {
+		$long =~ s/[[:cntrl:]]/?/g;
 		return $cgi->a({-href => $href, -class => "list subject",
 		                -title => to_utf8($long)},
 		       esc_html($short) . $extra);

-- 
1.6.3.1
Jakub Narebski· May 22, 2009, 15:39 UTC · re: Jakub Narebski · lore

[PATCH (lite)] gitweb: Sanitize title attribute in format_subject_html

Replace control characters with question mark '?' (like in chop_and_esc_str).

While at it: chop_and_escape_str doesn't need capturing group.
Noticed-by: Paul Gortmaker <paul.gortmaker@windriver.com>
Signed-off-by: Jakub Narebski <jnareb@gmail.com>
---
This version has more sane ratio of commit message length to actual
change...
 gitweb/gitweb.perl |    3 ++-
 1 files changed, 2 insertions(+), 1 deletions(-)
Show changes to gitweb/gitweb.perl +2 −1
diff --git a/gitweb/gitweb.perl b/gitweb/gitweb.perl
index 05702e4..1e7e2d8 100755
--- a/gitweb/gitweb.perl
+++ b/gitweb/gitweb.perl
@@ -1236,7 +1236,7 @@ sub chop_and_escape_str {
 	if ($chopped eq $str) {
 		return esc_html($chopped);
 	} else {
-		$str =~ s/([[:cntrl:]])/?/g;
+		$str =~ s/[[:cntrl:]]/?/g;
 		return $cgi->span({-title=>$str}, esc_html($chopped));
 	}
 }
@@ -1459,6 +1459,7 @@ sub format_subject_html {
 	$extra = '' unless defined($extra);
 
 	if (length($short) < length($long)) {
+		$long =~ s/[[:cntrl:]]/?/g;
 		return $cgi->a({-href => $href, -class => "list subject",
 		                -title => to_utf8($long)},
 		       esc_html($short) . $extra);

-- 
1.6.3.1
Jakub Narebski· May 22, 2009, 15:55 UTC · re: Jakub Narebski · lore

[RFC/PATCH (do not use)] gitweb: Introduce and use esc_attr to escape values of tag attributes

CGI.pm does by default slight escaping (simple_escape from CGI::Util) of all _attribute_ values (depending on the value of autoEscape(), by default on).

This escaping, at least in CGI.pm version 3.10 (most current version at CPAN is 3.43), is minimal: only '"', '&', '<' and '>' are escaped using named HTML entity references (&quot;, &amp;, &lt; and &gt; respectively). simple_escape does not do escaping of control characters such as ^X which are invalid in XHTML (in strict mode). Note that IIRC escaping '<' and '>' in attributes is not strictly necessary.

New 'esc_attr' subroutine can be used to do more complete escaping of attribute values, including dealing with control characters (forbidden in XHTML in strict validating mode); currently it replaces all control characters by '?' question mark. For esc_attr() to work correctly you have to turn off CGI.pm autoescaping to avoid double escaping.

While at it chop_and_esc_str now uses esc_attr instead of simply replacing control characters with '?' by itself.

The problem is that when autoescaping is turned off we would have to esc_attr all attributes containing user input (this includes result of href() subroutine), or risk either double escaping, or not escaping some fragment.

Alternate solution include:
* stripping of control characters before input is passed as attribute
  value, as it was done in chop_and_esc_str; this would include at
  minimum format_subject_html
* replacing either make_attributes from CGI.pm, or simple_escape
  subrotuine it uses, making it escape characters better
Noticed-by: Paul Gortmaker <paul.gortmaker@windriver.com>
Signed-off-by: Jakub Narebski <jnareb@gmail.com>

http://thread.gmane.org/gmane.comp.version-control.git/116755/focus=117539 --- This is abandoned version. Still... perhaps esc_attr would be of use to somebody... Also as negative example in archives.

 gitweb/gitweb.perl |   39 +++++++++++++++++++++++++++++++++------
 1 files changed, 33 insertions(+), 6 deletions(-)
Show changes to gitweb/gitweb.perl +33 −6
diff --git a/gitweb/gitweb.perl b/gitweb/gitweb.perl
index 05702e4..e505f2f 100755
--- a/gitweb/gitweb.perl
+++ b/gitweb/gitweb.perl
@@ -1027,7 +1027,7 @@ sub esc_param {
 	return $str;
 }
 
-# quote unsafe chars in whole URL, so some charactrs cannot be quoted
+# quote unsafe chars in whole URL, so some characters cannot be quoted
 sub esc_url {
 	my $str = shift;
 	$str =~ s/([^A-Za-z0-9\-_.~();\/;?:@&=])/sprintf("%%%02X", ord($1))/eg;
@@ -1036,6 +1036,26 @@ sub esc_url {
 	return $str;
 }
 
+# quote and escape tag attribute values; autoEscape has to be turned off
+# otherwise you would get double escaping for '&' ("escape" character)
+sub esc_attr {
+	my $str = shift;
+	return $str unless defined $str;
+
+	my %ent = ( # named HTML entities
+		'"' => '&quot;',
+		'&' => '&amp;',
+		# those are not strictly necessary
+		'<' => '&lt;',
+		'>' => '&gt;',
+	);
+	$str = to_utf8($str);
+	$str =~ s|([\"&<>])|$ent{$1}|eg;
+	$str =~ s|([[:cntrl:]])|?|eg; # alternative would be use quot_xxx($1)
+
+	return $str;
+}
+
 # replace invalid utf8 character with SUBSTITUTION sequence
 sub esc_html {
 	my $str = shift;
@@ -1236,8 +1256,10 @@ sub chop_and_escape_str {
 	if ($chopped eq $str) {
 		return esc_html($chopped);
 	} else {
-		$str =~ s/([[:cntrl:]])/?/g;
-		return $cgi->span({-title=>$str}, esc_html($chopped));
+		my $autoescape = $cgi->autoEscape(undef);
+		my $result = $cgi->span({-title=>esc_attr($str)}, esc_html($chopped));
+		$cgi->autoEscape($autoescape); # restore original value
+		return $result;
 	}
 }
 
@@ -1458,14 +1480,19 @@ sub format_subject_html {
 	my ($long, $short, $href, $extra) = @_;
 	$extra = '' unless defined($extra);
 
+	my $ret = '';
 	if (length($short) < length($long)) {
-		return $cgi->a({-href => $href, -class => "list subject",
-		                -title => to_utf8($long)},
+		my $autoescape = $cgi->autoEscape(undef);
+		# or just replace s/([[:cntrl:]])/?/g in -title
+		$ret = $cgi->a({-href => $href, -class => "list subject",
+		                -title => esc_attr($long)},
 		       esc_html($short) . $extra);
+		$cgi->autoEscape($autoescape); # restore original value
 	} else {
-		return $cgi->a({-href => $href, -class => "list subject"},
+		$ret = $cgi->a({-href => $href, -class => "list subject"},
 		       esc_html($long)  . $extra);
 	}
+	return $ret;
 }
 
 # format git diff header line, i.e. "diff --(git|combined|cc) ..."

-- 
1.6.3.1

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