Please describe the problem:

The function xmlIOParseDTD is supposed to free the xmlParserInputBufferPtr;
however it is possible for the function to return NULL without freeing the
buffer. What makes this a problem is that its possible for the function to
return NULL and free the buffer. Because the pointer is never set to NULL, its
impossible to test whether the pointer was in fact freed. As such, if the
pointer ever returned NULL it would be impossible to clean up properly.

The function xmlCtxtReadFile might have a memory leak. See the valgrind output
below. I haven't investigated further than what valgrind shows.

I am calling:

xmlFreeDoc();
xmlFreeParserCtxt();		
xmlCleanupParser();

None of which appear to cleanup this memory:

==17753== 16 bytes in 1 blocks are still reachable in loss record 1 of 2
==17753==    at 0x1B905301: calloc (vg_replace_malloc.c:176)
==17753==    by 0xB07364: _dlerror_run (in /lib/libdl-2.3.4.so)
==17753==    by 0xB06E3B: dlsym (in /lib/libdl-2.3.4.so)
==17753==    by 0x1B92ECA6: __errno_location (vg_libpthread.c:2127)
==17753==    by 0xB0E114: (within /usr/lib/libz.so.1.2.1.2)
==17753==    by 0x793FF1: (within /usr/lib/libxml2.so.2.6.16)
==17753==    by 0x79404F: (within /usr/lib/libxml2.so.2.6.16)
==17753==    by 0x79454A: __xmlParserInputBufferCreateFilename (in
/usr/lib/libxml2.so.2.6.16)
==17753==    by 0x79465F: xmlParserInputBufferCreateFilename (in
/usr/lib/libxml2.so.2.6.16)
==17753==    by 0x789F3C: xmlNewInputFromFile (in /usr/lib/libxml2.so.2.6.16)
==17753==    by 0x7A6A44: xmlCtxtReadFile (in /usr/lib/libxml2.so.2.6.16)
==17753==    by 0x8048890: main (main.c:129)


Steps to reproduce:
1. See above.


Actual results:
Memory leak.

Expected results:
Memory freed.

Does this happen every time?
Yes.

Other information:
The potential memory leak was confirmed by looking at the source for 2.6.23. The
second leak, reported by valgrind was reported on libxml2-2.6.16-6, which is a
repackaged Red Hat Enterprise version of the library. The reason I can't confirm
the second one is because I only have the source for 2.6.23.