Null pointer crash in ms-excel-util.c:758 on a fuzzed xlsx file

Git versions of glib, goffice, gnumeric, libgsf and libxml2.

Test case: http://jutaky.com/fuzzing/gnumeric_case_4096_1607.xlsx

$ ssconvert gnumeric_case_4096_1607.xlsx /tmp/out.gnumeric

==14545==ERROR: AddressSanitizer: SEGV on unknown address 0x000000000000 (pc 0x7f4e122bdf45 bp 0x7ffdb1730db0 sp 0x7ffdb1730a60 T0)
    #0 0x7f4e122bdf44 in xls_header_footer_import gnumeric/gnumeric/plugins/excel/ms-excel-util.c:758:10
    #1 0x7f4e125f6dbc in xlsx_CT_oddheader_end gnumeric/gnumeric/plugins/excel/xlsx-read.c:2005:2
    #2 0x7f4e33f76b81 in gsf_xml_in_end_element gnumeric/libgsf/gsf/gsf-libxml.c:863:3
    #3 0x7f4e32f40856 in xmlParseEndTag1 gnumeric/libxml2/parser.c:8747:9
    #4 0x7f4e32f4cd3a in xmlParseElement__internal_alias gnumeric/libxml2/parser.c:10191:2
    #5 0x7f4e32f47bd3 in xmlParseContent__internal_alias gnumeric/libxml2/parser.c:9990:6
    #6 0x7f4e32f4c039 in xmlParseElement__internal_alias gnumeric/libxml2/parser.c:10163:5
    #7 0x7f4e32f47bd3 in xmlParseContent__internal_alias gnumeric/libxml2/parser.c:9990:6
    #8 0x7f4e32f4c039 in xmlParseElement__internal_alias gnumeric/libxml2/parser.c:10163:5
    #9 0x7f4e32f70684 in xmlParseDocument__internal_alias gnumeric/libxml2/parser.c:10849:2
    #10 0x7f4e33f61c63 in gsf_xml_in_doc_parse gnumeric/libgsf/gsf/gsf-libxml.c:1338:2
    #11 0x7f4e125aacd8 in xlsx_parse_stream gnumeric/gnumeric/plugins/excel/xlsx-read.c:358:13
    #12 0x7f4e125b1bdf in xlsx_wb_end gnumeric/gnumeric/plugins/excel/xlsx-read.c:3996:3
    #13 0x7f4e33f76b81 in gsf_xml_in_end_element gnumeric/libgsf/gsf/gsf-libxml.c:863:3
    #14 0x7f4e32f40856 in xmlParseEndTag1 gnumeric/libxml2/parser.c:8747:9
    #15 0x7f4e32f4cd3a in xmlParseElement__internal_alias gnumeric/libxml2/parser.c:10191:2
    #16 0x7f4e32f70684 in xmlParseDocument__internal_alias gnumeric/libxml2/parser.c:10849:2
    #17 0x7f4e33f61c63 in gsf_xml_in_doc_parse gnumeric/libgsf/gsf/gsf-libxml.c:1338:2
    #18 0x7f4e125aacd8 in xlsx_parse_stream gnumeric/gnumeric/plugins/excel/xlsx-read.c:358:13
    #19 0x7f4e125a9652 in xlsx_file_open gnumeric/gnumeric/plugins/excel/xlsx-read.c:5153:4
    #20 0x7f4e34b35c80 in go_plugin_loader_module_func_file_open gnumeric/goffice/goffice/app/go-plugin-loader-module.c:282:3
    #21 0x7f4e34b49804 in go_plugin_file_opener_open gnumeric/goffice/goffice/app/go-plugin-service.c:685:2
    #22 0x7f4e34b57018 in go_file_opener_open gnumeric/goffice/goffice/app/file.c:417:2
    #23 0x7f4e364ddf2a in workbook_view_new_from_input gnumeric/gnumeric/src/workbook-view.c:1278:3
    #24 0x7f4e364deb20 in workbook_view_new_from_uri gnumeric/gnumeric/src/workbook-view.c:1337:9
    #25 0x4e0f21 in convert gnumeric/gnumeric/src/ssconvert.c:715:9
    #26 0x4decce in main gnumeric/gnumeric/src/ssconvert.c:903:9
    #27 0x7f4e2ef6c78f in __libc_start_main (/usr/lib/libc.so.6+0x2078f)
    #28 0x437b98 in _start (apps/bin/ssconvert+0x437b98)

AddressSanitizer can not provide additional info.
SUMMARY: AddressSanitizer: SEGV gnumeric/gnumeric/plugins/excel/ms-excel-util.c:758 xls_header_footer_import

--
Juha Kylmänen