Comment 15 for bug 939023

There's been some changes in Ubuntu's xserver recently for input device handling. (That's where the massive idiocy on my part about the -synaptics stuff earlier came from). That bug led to crashes when input devices were enabled/disabled and synaptics was in use, so I assumed that's all that was going on. However, that bug's fixed, and plus you're not using synaptics.

Thanks for collecting the more detailed backtrace. When you get a chance please also attach your full /etc/X11/xorg.conf and /var/log/Xorg.0.log. The output of `xinput list` might also be relevant.

The code is crashing in VAuditF, with this code:

VAuditF(const char *f, va_list args)
    ...
    len = vsnprintf(buf, sizeof(buf), f, args);

According to your trace, the f parameter being passed in is invalid:

#4 VAuditF (f=0xb <Address 0xb out of bounds>, args=0xb72e1318 "Segmentation fault") at ../../os/log.c:517

0xb certainly doesn't look like a valid pointer. It is curious what call #5 was. Maybe try installing xserver-xorg-input-evdev-dev?

More troubling is that the thing it was trying to print out is "Segmentation fault", which means this crash is occurring while trying to handle another crash, so the real problem is hidden.