CFTree: fix CFTreeRemove so it actually unlinks the node - #50
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CFTreeRemove() walked tree->_firstChild (the node's own children) instead of the parent's child list, and never assigned previousSibling, so the loop condition "child != previousSibling" simply ran to the end of the list and nothing was ever unlinked. It then called CFTreeFinalize() on the node while the parent still pointed at it. The node was therefore left linked into its parent; once it was released the parent held a dangling pointer (AddressSanitizer: heap-use-after-free in CFTreeGetChildCount/CFTreeFinalize after removing a child and releasing it), and the child count was never updated. Rewrite it to unlink the node from its parent's list of children, fix up the parent's _lastChild pointer when the last child is removed, and clear the node's _parent and _nextSibling. A node with no parent is left untouched. Adds regression tests covering removal of the first, middle, last and only child. The test also releases the tree before its children now: CFTreeAppendChild does not retain the child, so a child freed before the tree that links it would otherwise dangle.
# Conflicts: # ChangeLog # Tests/CFTree/basic.m
fredkiefer
reviewed
Aug 16, 2026
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| /* Fix up the parent's last-child pointer if we removed the last child. */ | ||
| if (parent->_lastChild == tree) |
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This could be done faster by having the test after line 206 (where we just set _lastChild to NULL) and after line 216 (where we set it to previousSibling). But we can leave that optimization to later.
This reminds me of having to implement linked lists in Pascal some 40 something years ago :-)
fredkiefer
approved these changes
Aug 16, 2026
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CFTreeRemove() walked tree->_firstChild (the node's own children) instead
of the parent's child list, and never assigned previousSibling, so the
loop condition "child != previousSibling" simply ran to the end of the
list and nothing was ever unlinked. It then called CFTreeFinalize() on
the node while the parent still pointed at it. The node was therefore
left linked into its parent; once it was released the parent held a
dangling pointer (AddressSanitizer: heap-use-after-free in
CFTreeGetChildCount/CFTreeFinalize after removing a child and releasing
it), and the child count was never updated.
Rewrite it to unlink the node from its parent's list of children, fix up
the parent's _lastChild pointer when the last child is removed, and clear
the node's _parent and _nextSibling. A node with no parent is left
untouched. Adds regression tests covering removal of the first, middle,
last and only child.
The test also releases the tree before its children now: CFTreeAppendChild
does not retain the child, so a child freed before the tree that links it
would otherwise dangle.