why local_preload_libraries does require a separate directory ?

From: Tomas Vondra <tv(at)fuzzy(dot)cz>
To: pgsql-hackers(at)postgreSQL(dot)org
Subject: why local_preload_libraries does require a separate directory ?
Date: 2011-12-03 14:56:46
Message-ID: 4EDA38AE.5030003@fuzzy.cz
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Hi,

why the libraries loaded using local_preload_libraries need to be placed
in a different subdirectory than libraries loaded using
shared_preload_libraries?

And why it does not use dynamic_library_path but a hardcoded path
'$libdir/plugins'?

I do understand that leaving the users to load whatever libraries they
want is a bad idea, but when the library is loaded from postgresql.conf
it should be safe.

Therefore I'd expect / propose this behaviour:

1) libs loaded from shared_preload_libraries/local_preload_libraries

- any paths are allowed (relative and absolute)
- relative paths are resolved using dynamic_library_path if
specified, $libdir otherwise
- absolute paths are allowed, may load libraries from other locations

2) libs loaded using LOAD

- check that the library is loaded from dynamic_library_path (if
specified), $libdir otherwise

AFAIK this prevents '..' type attacks and makes it easier to install
extensions (shared libs are installed to $libdir, so if you need to load
a library using local_preload_libraries, you have to copy it manually).

Tomas

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