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The PuTTY GUIs (Unix and Windows) maintain an in-memory event log
for display to users as they request. This uses ints for tracking
eventlog size, which is subject to memory exhaustion and (given
enough heap space) overflow attacks by servers (via, e.g., constant
rekeying).
Also a bounded log is more user-friendly. It is rare to want more
than the initial logging and the logging from a few recent rekey
events.
The Windows fix has been tested using Dr. Memory as a valgrind
substitute. No errors corresponding to the affected code showed up.
The Dr. Memory results.txt was split into a file per-error and then
grep Error $(grep -l windlg *)|cut -d: -f3-|sort |uniq -c
was used to compare. Differences arose from different usage of the GUI,
but no error could be traced to the code modified in this commit.
The Unix fix has been tested using valgrind. We don't destroy the
eventlog_stuff eventlog arrays, so we can't be entirely sure that we
don't leak more than we did before, but from code inspection it looks
like we don't (and anyways, if we leaked as much as before, just without
the integer overflow, well, that's still an improvement).