The loop that resets the query buffers was incorrecly using MAX_BUCKETS
to indicate the number of buckets to clear, which defaults to 10. If a
user lowers this value the loop would access a pointer beyond the number
of query buffers allocated.
Fix the problem by using the correct PGSM_MAX_BUCKETS GUC as the limit
to the loop.
This commit fix some issues when the query buffer overflows and
pg_stat_monitor attempts to dump its contents to a file.
The dump process is now as follows:
1. The dump will always be a full dump of the current query buffer,
meaning pg_stat_monitor will dump MAX_QUERY_BUFFER_BUCKET bytes to
the dump file.
2. When scanning the dump file, read chunks of size
MAX_QUERY_BUFFER_BUCKET, then look for the query ID using that chunk
and the query position metadata, this allows pg_stat_monitor to avoid
scanning the whole chunk when looking for a query ID.
The code in charge to read from/write to the dump file now takes into
account that read() and write() may return less bytes than what it was
asked for, the code now ensures that we actually read or write the
amount of bytes required (MAX_QUERY_BUFFER_BUCKET), also it handles
rare but posssible interrupts when doing those operations.
In SaveQueryText() we check for a possible overflow in the query buffer,
but if overflow would happen and pgsm_overflow_target value is 1 (the
default), then we dump the query buffer to a temporary file and reset
the buffer (start saving queries from the start of the buffer). The
problem is that after resetting the buffer we don't check if the current
query length would exceed the buffer size of MAX_QUERY_BUFFER_BUCKET, if
that is the case the buffer would overflow and probably crash the
process or in the worst case become an attack vector for exploitation.
This commit fix the problem by adding an additional check for overflow
after resetting the query buffer.
The GUC variable pgsm_overflow_target was pointing to the wrong index
(12, pgsm_track_planning) in the "GucVariable conf[MAX_SETTINGS]" array.
Adjusted it to the right index, 11.
Anastasia Alexadrova
Ibrar Ahmed
Evgeniy Patlan
Diego Fronza
Roma Novikov
Denys Kondratenko