xiccd[3214]: segfault at e4 ip 00005638ed3fd9a2

[Am0rphous]

Hi!
On Kali Linux i receive following error message. I don't know if every line is helpful. Running sudo dmesg gives

[   14.117639] systemd-journald[698]: /var/log/journal/d8dc8904695644168112634a06d6df4c/user-1000.journal: Journal file uses a different sequence number ID, rotating.
[   15.945916] panel-16-pulsea[2914]: memfd_create() called without MFD_EXEC or MFD_NOEXEC_SEAL set
[   16.397949] show_signal_msg: 8 callbacks suppressed
[   16.397952] xiccd[3214]: segfault at e4 ip 00005638ed3fd9a2 sp 00007ffe738ad830 error 4 in xiccd[5638ed3fa000+4000] likely on CPU 7 (core 1, socket 0)
[   16.397962] Code: bd 01 00 00 00 eb 91 90 48 89 df e8 d8 f8 ff ff eb c5 e8 11 cd ff ff 90 55 48 89 fd 53 48 83 ec 08 e8 c2 f8 ff ff 48 8b 7d 08 <8b> 97 e4 00 00 00 85 d2 7e 30 31 db 66 90 48 89 d8 ba 07 00 00 00

System (fully up to date)

• xiccd - 0.3.0+git
• Kali Linux Rolling (2023.4)
• Kernel: 6.6.9-amd64

[agalakhov]

Can you please compile xiccd with debug and get a stack trace?

[Am0rphous]

I tried earlier to download and compile the source code but met many obstacles and left it for a while.

I've now successfully compiled the code with debug symbols, but it's not very helpful, or I'm doing things wrong. I thought dmesg would show more helpful info, but it doesn't.

To compile xiccd i did following:

apt-get source xiccd
./configure --enable-debug
make
sudo make install
cp xiccd $(which xiccd)      #same as cp xiccd /usr/local/bin/xicc

The file /etc/xdg/autostart/xiccd.desktop seems to be a file for auto startin the app, but wasnt very helpful.

I received the error a while, eventhough the service seemed to run though.

[   24.049222] xiccd[3365]: segfault at e4 ip 000056025b905891 sp 00007ffe44c3d720 error 4 in xiccd[56025b901000+5000] likely on CPU 10 (core 4, socket 0)
[   24.049230] Code: 45 e8 48 8b 45 d8 48 8b 40 08 48 8b 4d e8 ba 07 00 00 00 48 89 ce 48 89 c7 e8 3b bb ff ff 83 45 fc 01 48 8b 45 d8 48 8b 40 08 <8b> 80 e4 00 00 00 39 45 fc 7c a9 48 8b 45 d8 48 89 c7 e8 01 ff ff

Lately I havent got the error, but I changed from Gnome to XFCE.

sudo dmesg doesn't seem to contain the error anymore.

[Am0rphous]

It seems the bug still persistent when running journalctl|grep xiccd

Jun 02 15:03:20 carbon dbus-daemon[1252]: [system] Activating via systemd: service name='org.freedesktop.ColorManager' unit='colord.service' requested by ':1.27' (uid=1000 pid=3646 comm="xiccd")
Jun 02 15:03:20 carbon kernel: xiccd[3646]: segfault at e4 ip 00005634a4510891 sp 00007ffed51a1d30 error 4 in xiccd[5634a450c000+5000] likely on CPU 7 (core 1, socket 0)
Jun 02 15:03:21 carbon systemd-coredump[3742]: Process 3646 (xiccd) of user 1000 dumped core.
                                               #0  0x00005634a4510891 setup_events (xiccd + 0x8891)
                                               #1  0x00005634a45108f0 randr_conn_private_start (xiccd + 0x88f0)
                                               #2  0x00005634a450fb24 randr_conn_start (xiccd + 0x7b24)
                                               #3  0x00005634a450e554 cd_connect_cb (xiccd + 0x6554)
                                               #21 0x00005634a450e6e5 main (xiccd + 0x66e5)
                                               #24 0x00005634a450ca91 _start (xiccd + 0x4a91)
Jun 02 15:04:49 carbon dbus-daemon[1084]: [system] Activating via systemd: service name='org.freedesktop.ColorManager' unit='colord.service' requested by ':1.23' (uid=1000 pid=3282 comm="xiccd")
Jun 02 15:04:49 carbon systemd-coredump[3474]: Process 3282 (xiccd) of user 1000 dumped core.
                                               #0  0x000055a3215d1891 setup_events (xiccd + 0x8891)
                                               #1  0x000055a3215d18f0 randr_conn_private_start (xiccd + 0x88f0)
                                               #2  0x000055a3215d0b24 randr_conn_start (xiccd + 0x7b24)
                                               #3  0x000055a3215cf554 cd_connect_cb (xiccd + 0x6554)
                                               #21 0x000055a3215cf6e5 main (xiccd + 0x66e5)
                                               #24 0x000055a3215cda91 _start (xiccd + 0x4a91)
Jun 02 15:08:22 carbon dbus-daemon[11070]: [session uid=0 pid=11068] Activating service name='org.freedesktop.portal.Desktop' requested by ':1.0' (uid=0 pid=11063 comm="gedit /etc/xdg/autostart/xiccd.desktop")
Jun 02 15:09:05 carbon dbus-daemon[11070]: [session uid=0 pid=11068] Activating service name='ca.desrt.dconf' requested by ':1.0' (uid=0 pid=11063 comm="gedit /etc/xdg/autostart/xiccd.desktop")

[Spinlocker]

Below is a copy of what I just wrote in this page of Launchpad bugtracker, and this seems related to what Am0rphous reports above.

[BOF]
Same for me with Xtightvnc server under Xubuntu jammy.

I recompiled xiccd in debug version and could track the crash I experienced down to (inline) function setup_events(), where member dpy of argument conn was null :

(gdb) bt
#0  0x00005650eb1cc6cf in setup_events (conn=0x565116b89400) at src/randr-conn-private.c:358
#1  0x00005650eb1cc732 in randr_conn_private_start (conn=0x565116b89400) at src/randr-conn-private.c:374
#2  0x00005650eb1cb82b in randr_conn_start (conn=0x565116b89430) at src/randr-conn.c:111
#3  0x00005650eb1ca162 in cd_connect_cb (src=0x565116b8a420, res=0x565116b8e820, user_data=0x7ffe19846ba0) at src/xiccd.c:577
#4  0x00007f38de68be39 in  () at /lib/x86_64-linux-gnu/libgio-2.0.so.0
#5  0x00007f38de68c05b in  () at /lib/x86_64-linux-gnu/libgio-2.0.so.0
#6  0x00007f38de7c7729 in  () at /lib/x86_64-linux-gnu/libcolord.so.2
#7  0x00007f38de68be39 in  () at /lib/x86_64-linux-gnu/libgio-2.0.so.0
#8  0x00007f38de68c05b in  () at /lib/x86_64-linux-gnu/libgio-2.0.so.0
#9  0x00007f38de6f563d in  () at /lib/x86_64-linux-gnu/libgio-2.0.so.0
#10 0x00007f38de68be39 in  () at /lib/x86_64-linux-gnu/libgio-2.0.so.0
#11 0x00007f38de68c05b in  () at /lib/x86_64-linux-gnu/libgio-2.0.so.0
#12 0x00007f38de6f7518 in  () at /lib/x86_64-linux-gnu/libgio-2.0.so.0
#13 0x00007f38de68be39 in  () at /lib/x86_64-linux-gnu/libgio-2.0.so.0
#14 0x00007f38de68c05b in  () at /lib/x86_64-linux-gnu/libgio-2.0.so.0
#15 0x00007f38de6ed73f in  () at /lib/x86_64-linux-gnu/libgio-2.0.so.0
#16 0x00007f38de68be39 in  () at /lib/x86_64-linux-gnu/libgio-2.0.so.0
#17 0x00007f38de68be7d in  () at /lib/x86_64-linux-gnu/libgio-2.0.so.0
#18 0x00007f38de9a8c44 in g_main_context_dispatch () at /lib/x86_64-linux-gnu/libglib-2.0.so.0
#19 0x00007f38de9fe2b8 in  () at /lib/x86_64-linux-gnu/libglib-2.0.so.0
#20 0x00007f38de9a82b3 in g_main_loop_run () at /lib/x86_64-linux-gnu/libglib-2.0.so.0
#21 0x00005650eb1ca31a in main (argc=1, argv=0x7ffe19846ce8) at src/xiccd.c:617
(gdb) print conn
$1 = (struct randr_conn *) 0x565116b89400
(gdb) print conn->dpy
$2 = (Display *) 0x0
(gdb) 

Function setup_events() has the following code:

static inline void
setup_events (struct randr_conn *conn)
{
	int s;
	for (s = 0; s < ScreenCount (conn->dpy); ++s) {
		Window w = RootWindow (conn->dpy, s);
		XRRSelectInput (conn->dpy, w,
				RRScreenChangeNotifyMask |
				RRCrtcChangeNotifyMask |
				RROutputChangeNotifyMask);
	}
	GSource *src = randr_source_new (conn);
	g_source_attach (src, NULL);
	g_source_unref (src);
}

Macro ScreenCount() is defined as follows in /usr/include/X11/Xlib.h:

#define ScreenCount(dpy) (((_XPrivDisplay)(dpy))->nscreens)

Therefore, using ScreenCount (conn->dpy) results in a null-pointer dereferencing.

Now for the cause: AFAICS, it seems that despite xiccd is already running on the target system, a new instance of xiccd is launched everytime VNC server is killed/restarted, and this new instance is the one which crashes. This may result from the custom version of $HOME/.vnc/Xstartup which is necessary to run Xtightvnc server on Xubuntu. Mine is as follows:

#!/bin/sh

#x-terminal-emulator -geometry 80x24+10+10 -ls -title "$VNCDESKTOP Desktop" &

# Fix to make GNOME and GTK stuff work
export XKL_XMODMAP_DISABLE=1
unset SESSION_MANAGER
unset DBUS_SESSION_BUS_ADDRESS

# exec /etc/X11/xinit/xinitrc
xrdb $HOME/.Xresources
xsetroot -solid grey

xfce4-session &

# before Ubuntu 18.04:
# gnome-settings-daemon &

# Ubuntu 18.04 and later:
/usr/lib/gnome-settings-daemon/gsd-xsettings &

Hope everything above makes sense, last time I performed some debugging is a long time ago...
[EOF]

[agalakhov]

Thank you! Will look at this.