For now, new selection objects are only created in ProcSetSelectionOwner()
when dixLookupSelection() can't find the requested one (returns BadMatch).
When somebody's trying to listen on a not-yet existing selection, via
XFixesSelectSelectionInput() -- XFIXES:SelectSelectionInput message -- he's
also getting BadMatch. The spec isn't explicitly clear on the exact behaviour
in those specific situations: it doesn't tell anything about selection's
lifetimes (when are they actually *created* or *destroyed*), just about their
ownership.
But there are real-world clients not expecting an error here and crashing
with a BadMatch error.
Since the spec doesn't mandate any Selection lifetime, it's safe to assume,
they can be created as-needed (as other related code paths already do).
Doing so ensures such an error cannot happen anymore.
XACE consumers get properly notified by the new Selection object creation
(eg. SElinux is attaching it's private data to it). And all callers already
prepared to get a cleared Selection object, because that's always been a
perfectly normal situation - Selection objects never get removed again,
just cleared.
Fixes: 601fd0fd8 - xfixes/xace: fix pointer type mismatch on XFixesSelectSelectionInput()
Signed-off-by: Enrico Weigelt, metux IT consult <info@metux.net>
Part-of: <https://gitlab.freedesktop.org/xorg/xserver/-/merge_requests/1574>
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