On Mon, Feb 26, 2018 at 09:48:39AM +0100, Ján Tomko wrote: > On Fri, Feb 23, 2018 at 06:21:15PM -0500, Cole Robinson wrote: > > lxml is a popular python XML processing library. It uses libxml2 > > behind the scenes, and registers custom callbacks via > > xmlSetExternalEntityLoader. However this can cause crashes if > > if an app uses both lxml and libxml2 together in the same process. > > > > This is a known limitation of lxml and libxml2 generally. It also > > prevents us from using lxml in virt-manager: > > > > https://bugzilla.redhat.com/show_bug.cgi?id=1544019 > > > > However it's easy enough to work around in libvirt, by unsetting the > > EntityLoader callback to a known state before we ask libxml2 to > > parse a file from disk. > > > > Signed-off-by: Cole Robinson <crobinso@xxxxxxxxxx> > > --- > > src/util/virxml.c | 5 +++++ > > 1 file changed, 5 insertions(+) > > > > diff --git a/src/util/virxml.c b/src/util/virxml.c > > index 6e87605ea..3e01794f9 100644 > > --- a/src/util/virxml.c > > +++ b/src/util/virxml.c > > @@ -810,9 +810,14 @@ virXMLParseHelper(int domcode, > > pctxt->sax->error = catchXMLError; > > > > if (filename) { > > + /* Reset any libxml2 file callbacks, other libs (like python lxml) > > + * may have set their own which can get crashy */ > > + xmlExternalEntityLoader origloader = xmlGetExternalEntityLoader(); > > + xmlSetExternalEntityLoader(xmlNoNetExternalEntityLoader); > > xml = xmlCtxtReadFile(pctxt, filename, NULL, > > XML_PARSE_NONET | > > XML_PARSE_NOWARNING); > > + xmlSetExternalEntityLoader(origloader); > > This does not look thread-safe at all - what if two libvirt threads > try to parse some XML at the same time? Indeed, that is not thread safe - I checked the libxml code and it just sets a static variable, not thread local. Regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :| -- libvir-list mailing list libvir-list@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/libvir-list
