On Thu, Apr 26, 2018 at 07:53:04PM +0900, Kyotaro HORIGUCHI wrote:
> I think this behavior is a bug. XLogReadRecord is considering the
> case but palloc_extended() breaks it. So in the attached, add a
> new flag MCXT_ALLOC_NO_PARAMERR to palloc_extended() and
> allocate_recordbuf calls it with the new flag. That alone fixes
> the problem. However, the patch frees read state buffer facing
> errorneous records since such records can leave a too-large
> buffer allocated.
This problem is already discussed here:
https://commitfest.postgresql.org/18/1516/
And here is the thread:
https://www.postgresql.org/message-id/flat/0A3221C70F24FB45833433255569204D1F8B57AD@G01JPEXMBYT05
Tsunakawa-san and I discussed a couple of approaches. Extending
palloc_extended so as an incorrect length does not result in an error is
also something that crossed by mind, but the length handling is
different on the backend and the frontend, so I discarded the idea you
are proposing here and instead relied on a check with AllocSizeIsValid,
which gives a more simple patch:
https://www.postgresql.org/message-id/20180314052753.GA16179%40paquier.xyz
This got no interest from committers yet unfortunately, but I think that
this is a real problem which should be back-patched :(
--
Michael