Comment 16 for bug 569879

Disassembling dixFreePrivates in gdb shows the crash is happening in:

                if (items[i].size)
                    xfree(privates[i].value);

Also, Kubuntu resets/regenerates the Xserver on log-out, where Gnome starts a new server on log-out.
The regeneration bit in the git commit below matches Scotts findings in comment #3.
Therefore in my opinion this patch from xserver git looks quite promising to fix this bug:

commit 4151a13c80f3afa43f88afcf19a7aeb16dace93a
Author: Francisco Jerez <email address hidden>
Date: Mon Oct 5 02:39:03 2009 +0200

    dix: Fix a double free in dixFreePrivates.

    It can be reproduced when the server is regenerated and for some
    reason the private keys are reassigned in a different order: a
    manually allocated private may get an index formerly used by a
    preallocated private. In that case it will first be manually freed and
    then again by dixFreePrivates, as items[i].size was never zeroed
    out. Do it in dixResetPrivates.

    Signed-off-by: Francisco Jerez <email address hidden>
    Acked-by: Eamon Walsh <email address hidden>
    Signed-off-by: Keith Packard <email address hidden>

diff --git a/dix/privates.c b/dix/privates.c
index 3a2deb8..e3e7274 100644
--- a/dix/privates.c
+++ b/dix/privates.c
@@ -303,6 +303,7 @@ dixResetPrivates(void)
     /* reset private descriptors */
     for (i = 1; i < nextPriv; i++) {
        *items[i].key = 0;
+ items[i].size = 0;
        DeleteCallbackList(&items[i].initfuncs);
        DeleteCallbackList(&items[i].deletefuncs);
     }

Can anyone test if this patch against xorg-server solves the crash? (I cannot reproduce the crash myself)