Heap-buffer overread in excel_read_XF on a fuzzed xls file.

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

Test case: http://jutaky.com/fuzzing/gnumeric_case_11510_28538.xls

==23140== ERROR: AddressSanitizer: heap-buffer-overflow on address 0x600600095363 at pc 0x7f0a193e0717 bp 0x7fff7b12d0f0 sp 0x7fff7b12d0e8
READ of size 1 at 0x600600095363 thread T0
    #0 0x7f0a193e0716 in excel_read_XF /gnumeric/plugins/excel/ms-excel-read.c:2687
    #1 0x7f0a1941f2e8 in excel_read_workbook /gnumeric/plugins/excel/ms-excel-read.c:7103
    #2 0x7f0a19394c2c in excel_enc_file_open /gnumeric/plugins/excel/boot.c:193
    #3 0x7f0a193958ca in excel_file_open /gnumeric/plugins/excel/boot.c:250
    #4 0x7f0a3ae2600e in go_plugin_loader_module_func_file_open /goffice/goffice/app/go-plugin-loader-module.c:282
    #5 0x7f0a3ae2ef70 in go_plugin_file_opener_open /goffice/goffice/app/go-plugin-service.c:685 (discriminator 1)
    #6 0x7f0a3ae3b8bf in go_file_opener_open /goffice/goffice/app/file.c:417
    #7 0x7f0a3bf91684 in workbook_view_new_from_input /gnumeric/src/workbook-view.c:1281
    #8 0x7f0a3bf91e73 in workbook_view_new_from_uri /gnumeric/src/workbook-view.c:1341
    #9 0x40a6e0 in main /gnumeric/src/main-application.c:322
    #10 0x7f0a36719bc4 in __libc_start_main ??:?
    #11 0x403de8 in _start ??:?
0x600600095363 is located 0 bytes to the right of 19-byte region [0x600600095350,0x600600095363)

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Juha Kylmänen
Research Assistant, OUSPG