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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - Invalid memory access in xcb_icccm_get_wm_class_from_reply"
href="https://bugs.freedesktop.org/show_bug.cgi?id=93268">93268</a>
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<th>Summary</th>
<td>Invalid memory access in xcb_icccm_get_wm_class_from_reply
</td>
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<th>Product</th>
<td>XCB
</td>
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<th>Version</th>
<td>unspecified
</td>
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<th>Hardware</th>
<td>All
</td>
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<th>OS</th>
<td>All
</td>
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<th>Status</th>
<td>NEW
</td>
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<th>Severity</th>
<td>normal
</td>
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<th>Priority</th>
<td>medium
</td>
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<th>Component</th>
<td>Utils
</td>
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<th>Assignee</th>
<td>xcb@lists.freedesktop.org
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<th>Reporter</th>
<td>jpinon@free.fr
</td>
</tr>
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<th>QA Contact</th>
<td>xcb@lists.freedesktop.org
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<p>
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<pre>I fell in a case where in xcb_icccm_get_wm_class_from_reply, the reply was
empty, i.e., in following snippet from icccm.c, len was 0, and reply->length
was 0 also.
int len = xcb_get_property_value_length(prop->_reply);
if(len < reply->length * 4)
prop->instance_name[len] = 0;
else
prop->instance_name[len-1] = 0;
in this case, prop->instance_name[-1] is set to 0, and the following
strlen(prop->instance_name) may access invalid memory.
This may be reproduced under openbox window manager, under which there is this
window triggering the bug :
If xwininfo is compiled without icccm :
./xwininfo -tree -root | grep Openbox
0xe0008b "Openbox": ("" (none)) 1x1+-100+-100 +-100+-100
If xwininfo is compiled with icccm :
./xwininfo -tree -root | grep Openbox
0xe0008b "Openbox": ("" "") 1x1+-100+-100 +-100+-100
The second case triggers the Invalid memory access</pre>
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