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Re: [xml] Problem resolving relative URIs during catalog resolution, potential regression as of libxml2 2.9.2 (patch included)

  Hi Matthias,

 it took a while but I looked at this today, indeed that's a serious regression
however your patch needed a bit of work to avoid potential segfaults. Also
I found that condition in a couple of place in the code. Resulting fix is
commited to git head:

https://git.gnome.org/browse/libxml2/commit/?id=3daee3f159a1f962278e6f92572b7749b2b2babb

  thanks for the report !

Daniel

On Thu, Nov 24, 2016 at 02:20:36PM +0000, Matthias Pigulla wrote:

Hello libxml2 developers,

TL/DR:

./testURI --base file:///some/where file

Without patch: file:/some/file
With patch: file:///some/file

Full report:

I am using PHP to read a simple XML file and see a regression between
libxml 2.9.1 and 2.9.2, with the problem still present in 2.9.4.

File:
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN³
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd";>
<html xmlns=3D"http://www.w3.org/1999/xhtml";>
<body>
<div>test &copy; </div>
</body>
</html>


I am running this on Debian and have installed the w3c-dtd-xhtml pacakge,
relying on system tooling to generate the catalog definitions in /etc/xml.
If it helps, I can post a tarball with all relevant files from /etc/xml
and /usr/share/xml/xhtml somewhere.

The resulting catalog will contain file:///etc/... references to other
files, eventually pointing to file:///usr/share/xml/somewhere... and
finally contain relative references like 'uri="xhtml1-strict.dtd"'.


Due to a glitch in xmlBuildURI, interpreting this relative URI with a base
of "file:///usr/share/xml/xhtml/schema/dtd/1.0/catalog.xml" ends up as
"file:/usr/share/xml/xhtml/schema/dtd/1.0/xhtml1-strict.dtd" with only a
single slash following the "file:".

Further down the road, this is interpreted as a file path and passed to
system calls, as can be seen in this strace output:

stat("file:/usr/share/xml/xhtml/schema/dtd/1.0/xhtml1-strict.dtd³,
0x7fff7f56fda0) = -1 ENOENT (No such file or directory)
stat("file:/usr/share/xml/xhtml/schema/dtd/1.0/xhtml1-strict.dtd³,
0x7fff7f56fd50) = -1 ENOENT (No such file or directory)

Immediately after, PHP fails with a PHP Notice: DOMDocument::loadXML():
failed to load external entity
"file:/usr/share/xml/xhtml/schema/dtd/1.0/xhtml1-strict.dtd" in Entity,
line ...

The patch solves the problem for me.


Relevant changes:
https://git.gnome.org/browse/libxml2/commit/?id=8eb55d782a2b9afacc793869489
1cc6fad7b42a5
https://git.gnome.org/browse/libxml2/commit/?id=beb7281055dbf0ed4d041022a67
c6c5cfd126f25
Also see https://mail.gnome.org/archives/xml/2014-December/msg00000.html.


Please let me know if a test case for this is needed (would need
instructions how/where to write this).

Best regards
Matthias




diff --git a/uri.c b/uri.c
index 2bd5720..6e09018 100644
--- a/uri.c
+++ b/uri.c
@@ -2024,7 +2024,7 @@ xmlBuildURI(const xmlChar *URI, const xmlChar *base) {
     }
     if (bas->authority != NULL)
        res->authority = xmlMemStrdup(bas->authority);
-    else if (bas->server != NULL) {
+    else if ((bas->server != NULL) || (bas->port == -1)) {
        res->server = xmlMemStrdup(bas->server);
        if (bas->user != NULL)
            res->user = xmlMemStrdup(bas->user);



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-- 
Daniel Veillard      | Red Hat Developers Tools http://developer.redhat.com/
veillard redhat com  | libxml Gnome XML XSLT toolkit  http://xmlsoft.org/
http://veillard.com/ | virtualization library  http://libvirt.org/
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