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SubjectRe: As 2.0 looms
Date
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Marek Michalkiewicz wrote:
>
> Alain KNAFF:
> > >You decide
> > >which one you want to use at link time (default is to ignore LD_xxx -
> > >it's not necessary except for testing new shared libraries). I think
> >
> > LD_xxx is also needed for programs such as zlibc, which work by
> > redefining certain library calls. Ignoring LD_xxx by default would
> > make any such program impractical.
>
> OK, thanks for pointing this out. But you can still make the binaries
> use LD_xxx if you want.
>
> There should be a secure LD_PRELOAD equivalent - use a system-wide config
> file instead of environment variables. I think David Engel is working on
> it (specifying libraries to preload in /etc/ld.so.preload). Is it OK
> for zlibc, or does every user really have to be able to redefine library
> calls on their own? (/etc/ld.so.preload would be useful for other things
> as well, like replacing crypt() with something better.)
>
> Marek
>


There are a lot of things we don't have to have, but which are
still convenient. The average end user probably has little use
for LD_PRELOAD, but programmers do.

Personally, I like being able to use LD_PRELOAD to load malloc() and
friends replacements that have better error checking (I'm thinking
of libdmalloc by gray.watson@letters.com). Granted I don't use it
a *lot*, but it is really nice when I do.

Overall, as scary as the LD_PRELOAD thing was at first, Linux's
ld.so seems to handle it in a safe way: only allow it if the
programmer could have relinked the program himself and done it
anyway.

The telnet security hole should just be a reminder that environment
variables are just like command line arguments, and it is dangerous
to allow aribitrary users to give arbitrary arguments to a
program executed by root.

Finally, using a system-wide config file would largely ruin the
main point of LD_PRELOAD as I understand it; I thought the point
was to invoke a program with different libraries than it would
get by default?


My vote is to leave the LD_xxx system as it is, and keep an eye
out for:

a) places the system really lets users gain a privilage
they wouldn't have before.

b) places where unprivilaged users can specify an arbitrary
environment variable for a program that root will execute.



lex


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