CFTree: fix null-pointer dereferences in child handling#49
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Two ways to crash via the public API:
* CFTreePrependChild() set tree->_lastChild = NULL (instead of the new
child) when the tree had no children, so prepending the first child
left _lastChild NULL. A subsequent CFTreeAppendChild() then
dereferenced it (tree->_lastChild->_nextSibling), a NULL write.
* CFTreeGetChildAtIndex() walked the sibling list without checking for
the end, so an index past the last child dereferenced NULL.
Set _lastChild to the new child, and stop the walk at the end of the
list (returning NULL for an out-of-range index). Adds regression tests
(the existing test prepended only after an append, so it never exercised
the empty-tree path).
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Two ways to crash via the public API:
CFTreePrependChild() set tree->_lastChild = NULL (instead of the new
child) when the tree had no children, so prepending the first child
left _lastChild NULL. A subsequent CFTreeAppendChild() then
dereferenced it (tree->_lastChild->_nextSibling), a NULL write.
CFTreeGetChildAtIndex() walked the sibling list without checking for
the end, so an index past the last child dereferenced NULL.
Set _lastChild to the new child, and stop the walk at the end of the
list (returning NULL for an out-of-range index). Adds regression tests
(the existing test prepended only after an append, so it never exercised
the empty-tree path).