Re: [Patch] Check file type before calling AllocateFile() for files out of pg data directory to avoid potential issues (e.g. hang).

Hi,

On 2019-04-24 12:46:15 +0800, Paul Guo wrote:
> This is, in theory, not a 100% bug, but it is probably not unusual to see
> conflicts of files between postgresql sqls and other applications on the
> same node so I think the fix is needed. I checked all code that calls
> AllocateFile() and wrote a simple patch to do sanity check (if the file
> exists it must be a regular file) for those files which are probably out of
> the postgres data directories which we probably want to ignore. This is
> actually not a perfect fix since it is not atomic (check and open), but it
> should fix most of the scenarios. To be perfect, we might want to refactor
> AllocateFile() to allow atomic check&create using either 'x' in fopen()
> or O_EXCL in open(), also it seems that we might not want to create temp
> file for AllocateFile() with fixed filenames. This is beyond of this patch
> of course.

This seems like a bad idea to me. IMO we want to support using a pipe
etc here. If the admin creates a fifo like this without attaching a
program it seems like it's their fault.

Greetings,

Andres Freund