Re: [musl] [PATCH] ldso/dynlink: Protect LD_ env vars from getting clobbered by apps

[Elvis Pranskevichus <elvis@edgedb.com>]

On Wednesday, August 17, 2022 8:29:05 AM PDT Rich Felker wrote:
> On Tue, Aug 16, 2022 at 10:45:45PM -0700, Elvis Pranskevichus wrote:
> > There is no guarantee that the environment block will remain intact.
> > For example, PostgreSQL clobbers argv/environ area to implement its
> > "setproctitle" emulation on non-BSD [1], and there is a popular
> > Python library inspired by it [2].  As a result, setting
> > `LD_LIBRARY_PATH` or `LD_PRELOAD` has no effect on Postgres
> > subprocesses when linking against musl.
> 
> This is explicitly not allowed and is UB. This memory is not available
> for the application to clobber, and code attempting to do that needs
> to be patched out. Aside from the general principle, POSIX is very
> clear in the specification of environ:
> 
>     "Any application that directly modifies the pointers to which the
>     environ variable points has undefined behavior."

I understand that what Postgres et al are doing is a nasty hack.  My 
thinking was that it is a question of compatibility with glibc's 
behavior, which seems to tolerate these shenanigans (at least with 
respect to `LD_*` variables.  Good point regarding the allocator bringup 
overhead, I haven't thought of that.

Thanks,

                                Elvis