Re: Reject sub-minimum ErrorResponse length in read_kind_from_backend.

> Emond Papegaaij reported a bug in read_kind_from_backend.
>
> read_kind_from_backend() handles a backend ErrorResponse on the V3
> path by reading the 4-byte length field, palloc'ing a buffer sized at
> ntohl(len), and immediately memcpy()ing all 4 bytes of the
> network-order length back into that buffer. When a backend (malicious,
> buggy, or speaking a non-V3 dialect that has slipped past earlier
> checks) sends a length below 4 ― i.e. in {0,1,2,3} ― the palloc
> chunk is smaller than sizeof(len) and the memcpy overruns the heap
> allocation. The follow-up `len -= 4` then underflows to a huge
> unsigned value, which the subsequent `repalloc(unread_p, sizeof(len) +
> len)` may wrap, and pool_read2() is asked for a colossal payload ―
> all on top of an already-corrupted heap.
>
> Reject any ntohl(len) below sizeof(len) up front with ereport(ERROR,
> ...). The error path is the existing longjmp-based one used by every
> other malformed-input check in this function, so the connection is
> torn down cleanly without touching unread_p.
>
> Patch attached.

Peng and Koshino reviewed the patch off-list and they agreed that it
looks good. I have pushed the patch to all supported branches.

Thank you, Emond.

https://git.postgresql.org/gitweb/?p=pgpool2.git;a=commit;h=912d7ce0b9d3a29a343a4b828e86fc05c0f47755
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Tatsuo Ishii
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