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segfault when no X11 is available / DISPLAY=""

Running a simple python gtk application (e.g. the hello world example from [1]) without access to the X server crashes.

Test:

  • Save example from [1] as hello.py
  • run: DISPLAY="" python3 hello.py

This looks like a null pointer deref. I'll paste an ASAN stack trace below.

[1] https://python-gtk-3-tutorial.readthedocs.io/en/latest/introduction.html

==9099==ERROR: AddressSanitizer: SEGV on unknown address 0x000000000018 (pc 0x7f323789bf78 sp 0x7ffca73d0320 bp 0x6290000a2020 T0)
    #0 0x7f323789bf77 in _gtk_settings_get_screen /var/tmp/portage/x11-libs/gtk+-3.24.2/work/gtk+-3.24.2/gtk/gtksettings.c:3300
    #1 0x7f32375d9b3f in gtk_css_value_icon_theme_compute /var/tmp/portage/x11-libs/gtk+-3.24.2/work/gtk+-3.24.2/gtk/gtkcssiconthemevalue.c:84
    #2 0x7f3237617d17 in gtk_css_static_style_compute_value /var/tmp/portage/x11-libs/gtk+-3.24.2/work/gtk+-3.24.2/gtk/gtkcssstaticstyle.c:237
    #3 0x7f32375ee55c in _gtk_css_lookup_resolve /var/tmp/portage/x11-libs/gtk+-3.24.2/work/gtk+-3.24.2/gtk/gtkcsslookup.c:122
    #4 0x7f3237617bf3 in gtk_css_static_style_new_compute /var/tmp/portage/x11-libs/gtk+-3.24.2/work/gtk+-3.24.2/gtk/gtkcssstaticstyle.c:195
    #5 0x7f3237617ca4 in gtk_css_static_style_get_default /var/tmp/portage/x11-libs/gtk+-3.24.2/work/gtk+-3.24.2/gtk/gtkcssstaticstyle.c:164
    #6 0x7f32375f0145 in gtk_css_node_init /var/tmp/portage/x11-libs/gtk+-3.24.2/work/gtk+-3.24.2/gtk/gtkcssnode.c:667
    #7 0x7f323ade294e in g_type_create_instance (/usr/lib64/libgobject-2.0.so.0+0x7b94e)
    #8 0x7f323ada242e (/usr/lib64/libgobject-2.0.so.0+0x3b42e)
    #9 0x7f323ada4b80 in g_object_new_with_properties (/usr/lib64/libgobject-2.0.so.0+0x3db80)
    #10 0x7f323ada63d3 in g_object_new (/usr/lib64/libgobject-2.0.so.0+0x3f3d3)
    #11 0x7f3237625cc9 in gtk_css_widget_node_new /var/tmp/portage/x11-libs/gtk+-3.24.2/work/gtk+-3.24.2/gtk/gtkcsswidgetnode.c:297
    #12 0x7f3237a21715 in gtk_widget_init /var/tmp/portage/x11-libs/gtk+-3.24.2/work/gtk+-3.24.2/gtk/gtkwidget.c:4420
    #13 0x7f323ade294e in g_type_create_instance (/usr/lib64/libgobject-2.0.so.0+0x7b94e)
    #14 0x7f323ada242e (/usr/lib64/libgobject-2.0.so.0+0x3b42e)
    #15 0x7f323ada5364 in g_object_newv (/usr/lib64/libgobject-2.0.so.0+0x3e364)
    #16 0x7f323aef905e (/usr/lib64/python3.6/site-packages/gi/_gi.cpython-36m-x86_64-linux-gnu.so+0x2e05e)
    #17 0x7f323af09bc7 (/usr/lib64/python3.6/site-packages/gi/_gi.cpython-36m-x86_64-linux-gnu.so+0x3ebc7)
    #18 0x7f323ea6ca1b (/usr/lib64/libpython3.6m.so.1.0+0x231a1b)
    #19 0x7f323e982241 in _PyObject_FastCallDict (/usr/lib64/libpython3.6m.so.1.0+0x147241)
    #20 0x7f323e9ca816 (/usr/lib64/libpython3.6m.so.1.0+0x18f816)
    #21 0x7f323e981ebf in PyObject_Call (/usr/lib64/libpython3.6m.so.1.0+0x146ebf)
    #22 0x7f323eb629b9 in _PyEval_EvalFrameDefault (/usr/lib64/libpython3.6m.so.1.0+0x3279b9)
    #23 0x7f323eb57e50 (/usr/lib64/libpython3.6m.so.1.0+0x31ce50)
    #24 0x7f323eb71384 in _PyFunction_FastCallDict (/usr/lib64/libpython3.6m.so.1.0+0x336384)
    #25 0x7f323e98243d in _PyObject_FastCallDict (/usr/lib64/libpython3.6m.so.1.0+0x14743d)
    #26 0x7f323e9829d8 in _PyObject_Call_Prepend (/usr/lib64/libpython3.6m.so.1.0+0x1479d8)
    #27 0x7f323e981ebf in PyObject_Call (/usr/lib64/libpython3.6m.so.1.0+0x146ebf)
    #28 0x7f323ea80733 (/usr/lib64/libpython3.6m.so.1.0+0x245733)
    #29 0x7f323ea76e01 (/usr/lib64/libpython3.6m.so.1.0+0x23be01)
    #30 0x7f323e982241 in _PyObject_FastCallDict (/usr/lib64/libpython3.6m.so.1.0+0x147241)
    #31 0x7f323eb589b0 (/usr/lib64/libpython3.6m.so.1.0+0x31d9b0)
    #32 0x7f323eb6522e in _PyEval_EvalFrameDefault (/usr/lib64/libpython3.6m.so.1.0+0x32a22e)
    #33 0x7f323eb57e50 (/usr/lib64/libpython3.6m.so.1.0+0x31ce50)
    #34 0x7f323eb58fbd in PyEval_EvalCodeEx (/usr/lib64/libpython3.6m.so.1.0+0x31dfbd)
    #35 0x7f323eb58fea in PyEval_EvalCode (/usr/lib64/libpython3.6m.so.1.0+0x31dfea)
    #36 0x7f323ebc5c47 (/usr/lib64/libpython3.6m.so.1.0+0x38ac47)
    #37 0x7f323ebcaf94 in PyRun_FileExFlags (/usr/lib64/libpython3.6m.so.1.0+0x38ff94)
    #38 0x7f323ebcb271 in PyRun_SimpleFileExFlags (/usr/lib64/libpython3.6m.so.1.0+0x390271)
    #39 0x7f323ebff975 in Py_Main (/usr/lib64/libpython3.6m.so.1.0+0x3c4975)
    #40 0x401337 in main (/usr/bin/python3.6m+0x401337)
    #41 0x7f323e274ae6 in __libc_start_main (/lib64/libc.so.6+0x21ae6)
    #42 0x4014c9 in _start (/usr/bin/python3.6m+0x4014c9)