[virt-tools-list] Crash in libxml python callback running tests

[Daniel P. Berrangé]

I built libvirt using --prefix=/usr/local, and then did *not* run
'make install'.

I then tried to run virt-manager tests

  ../libvirt/run python3 setup.py test

It crashed & burned. Initially the problem is that the
virConnectGetCPUModelNames API call on the test driver fails
because the cpu_map.xml file isn't installed yet. A libxml
error is raised because it fails to open this file to parse
it, here we end up calling back into python and crash and
burn

Program received signal SIGSEGV, Segmentation fault.
0x00007ffff7994882 in PyObject_Call () from /lib64/libpython3.6m.so.1.0
(gdb) bt
#0  0x00007ffff7994882 in PyObject_Call () at /lib64/libpython3.6m.so.1.0
#1  0x00007fffe351cede in libxml_xmlErrorFuncHandler () at /usr/lib64/python3.6/site-packages/libxml2mod.so
#2  0x00007fffebbe412e in xmlReportError () at /lib64/libxml2.so.2
#3  0x00007fffebbe599d in __xmlRaiseError () at /lib64/libxml2.so.2
#4  0x00007fffebc12827 in __xmlLoaderErr () at /lib64/libxml2.so.2
#5  0x00007fffebbe79c7 in xmlNewInputFromFile () at /lib64/libxml2.so.2
#6  0x00007fffebc14a57 in xmlDefaultExternalEntityLoader () at /lib64/libxml2.so.2
#7  0x00007fffebc1488d in xmlLoadExternalEntity () at /lib64/libxml2.so.2
#8  0x00007fffebc01767 in xmlCtxtReadFile () at /lib64/libxml2.so.2
#9  0x00007fffed85b194 in virXMLParseHelper (domcode=domcode at entry=31, filename=0x555555b18520 "/usr/local/share/libvirt/cpu_map.xml", xmlStr=xmlStr at entry=0x0, url=url at entry=0x0, ctxt=ctxt at entry=0x7fffffff8d20) at util/virxml.c:813
#10 0x00007fffed8e41f2 in cpuMapLoad (arch=arch at entry=0x7fffed9fd263 "x86", cb=cb at entry=0x7fffed8dd4a0 <x86MapLoadCallback>, data=0x555555a007d0)
    at cpu/cpu_map.c:105
#11 0x00007fffed8e1085 in virCPUx86LoadMap () at cpu/cpu_x86.c:1399
#12 0x00007fffed8e1085 in virCPUx86DriverOnceInit () at cpu/cpu_x86.c:1413
#13 0x00007fffed8e11e9 in virCPUx86DriverOnce () at cpu/cpu_x86.c:160
#14 0x00007ffff7666b37 in __pthread_once_slow () at /lib64/libpthread.so.0
#15 0x00007fffed8dcce7 in virCPUx86DriverInitialize () at cpu/cpu_x86.c:160
#16 0x00007fffed8dcda2 in virCPUx86GetMap () at cpu/cpu_x86.c:1425
#17 0x00007fffed8dcda2 in virCPUx86GetModels (models=0x7fffffff8ec8) at cpu/cpu_x86.c:2820
#18 0x00007fffed91675c in virConnectGetCPUModelNames (conn=0x555555cb92b0, arch=0x7fffee0aba00 "x86_64", models=0x7fffffff8ec8, flags=0)
    at libvirt-host.c:1028
#19 0x00007fffedd131ec in libvirt_virConnectGetCPUModelNames () at /usr/lib64/python3.6/site-packages/libvirtmod.cpython-36m-x86_64-linux-gnu.so


Valgrind gives similar trace:


==18849== Invalid read of size 4
==18849==    at 0x4F5A882: PyObject_Call (in /usr/lib64/libpython3.6m.so.1.0)
==18849==    by 0x1BD27EDD: ??? (in /usr/lib64/python3.6/site-packages/libxml2mod.so)
==18849==    by 0x12FB412D: ??? (in /usr/lib64/libxml2.so.2.9.7)
==18849==    by 0x12FB599C: __xmlRaiseError (in /usr/lib64/libxml2.so.2.9.7)
==18849==    by 0x12FE2826: __xmlLoaderErr (in /usr/lib64/libxml2.so.2.9.7)
==18849==    by 0x12FB79C6: xmlNewInputFromFile (in /usr/lib64/libxml2.so.2.9.7)
==18849==    by 0x12FE4A56: ??? (in /usr/lib64/libxml2.so.2.9.7)
==18849==    by 0x12FE488C: xmlLoadExternalEntity (in /usr/lib64/libxml2.so.2.9.7)
==18849==    by 0x12FD1766: xmlCtxtReadFile (in /usr/lib64/libxml2.so.2.9.7)
==18849==    by 0x1136B193: virXMLParseHelper (virxml.c:813)
==18849==    by 0x113F41F1: cpuMapLoad (cpu_map.c:105)
==18849==    by 0x113F1084: virCPUx86LoadMap (cpu_x86.c:1399)
==18849==    by 0x113F1084: virCPUx86DriverOnceInit (cpu_x86.c:1413)
==18849==  Address 0x20 is not stack'd, malloc'd or (recently) free'd


This kind of smells like the same kind of problem that the python lxml
library has co-existing with otehr stuff that uses libxml, but since
AFAIK virt-manager isn't using lxml, I'm wondering what's causing this
crash ?

Regards,
Daniel
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