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MDEV-28268: Server crashes in Expression_cache_tracker::fetch_current_stats

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Expression_cache_tmptable object uses an Expression_cache_tracker object
to report the statistics.

In the common scenario, Expression_cache_tmptable destructor sets
tracker->cache=NULL. The tracker object survives after the expression
cache is deleted and one may call cache_tracker->fetch_current_stats()
for it with no harm.

However a degenerate cache with no parameters does not set
tracker->cache=NULL in Expression_cache_tmptable destructor which
results in an attempt to use freed data in the
cache_tracker->fetch_current_stats() call.

Fixed by setting tracker->cache to NULL and wrapping the assignment into
a function.
This commit is contained in:
Sergei Petrunia
2022-04-26 23:03:34 +03:00
parent c711abd182
commit eea15803ec
4 changed files with 98 additions and 1 deletions
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4
sql/sql_expression_cache.cc
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@ -63,7 +63,7 @@ void Expression_cache_tmptable::disable_cache()
cache_table= NULL;
update_tracker();
if (tracker)
tracker->cache= NULL;
tracker->detach_from_cache();
}
@ -188,6 +188,8 @@ Expression_cache_tmptable::~Expression_cache_tmptable()
else
{
update_tracker();
if (tracker)
tracker->detach_from_cache();
tracker= NULL;
}
}