Fix panic-safety in LinkedHashMap::clear (double-free on panicking value Drop) - #9
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…lue Drop) clear frees the value nodes (running each value's user-controlled Drop) and resets the sentinel's guard links afterwards. A value Drop that panics partway leaves the reset unrun, so the guard still points into freed memory; the map's own destructor then walks that chain again and frees it a second time -- a double-free reachable from safe Rust. Reset the guard links before freeing so unwinding leaves an empty, self-consistent list. LinkedHashSet::clear delegates to LinkedHashMap::clear and is fixed by the same change. Adds a regression test.
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Found while auditing this crate's unsafe teardown paths for panic-safety.
Summary
clear frees the value nodes, running each value's Drop, then resets the guard
links. If a value's Drop panics after some nodes are freed, the reset is skipped
and the sentinel still points at freed memory. The map's destructor later walks
that chain and frees it again, a double-free (CWE-415) reachable from safe Rust.
Fix
Reset the guard links before freeing instead of after. The sentinel then points
at an empty list, so a panic during freeing can't reach the second traversal. On
panic the unreached nodes leak, which is safe. LinkedHashSet::clear delegates to
LinkedHashMap::clear and is fixed by the same change.
Verification
Added clear_panicking_value_drop_is_sound: values that panic on Drop are cleared
under catch_unwind, then the map is dropped. Without the fix the second traversal
double-frees the chain (glibc "double free detected", SIGABRT); with the fix it
unwinds cleanly. Existing tests pass. Confirmed on 0.3.2.