NetBSD Problem Report #47509

From www@NetBSD.org  Mon Jan 28 22:50:31 2013
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Date: Mon, 28 Jan 2013 22:50:30 +0000 (UTC)
From: csunstrum@coverity.com
Reply-To: csunstrum@coverity.com
To: gnats-bugs@NetBSD.org
Subject: ld.elf_so does not expand variables (such as $PLATFORM) in LD_PRELOAD
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>Number:         47509
>Category:       bin
>Synopsis:       ld.elf_so does not expand variables (such as $PLATFORM) in LD_PRELOAD
>Confidential:   no
>Severity:       serious
>Priority:       high
>Responsible:    bin-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Mon Jan 28 22:55:00 +0000 2013
>Originator:     Caleb Sunstrum
>Release:        5.0.2
>Organization:
Coverity
>Environment:
NetBSD t-netbsd5x64-vm01 5.0.2 NetBSD 5.0.2 (GENERIC) #0: Sat Feb  6 13:44:19 UTC 2010  builds@b8.netbsd.org:/home/builds/ab/netbsd-5-0-2-RELEASE/amd64/201002061851Z-obj/home/builds/ab/netbsd-5-0-2-RELEASE/src/sys/arch/amd64/compile/GENERIC amd64

>Description:
When setting LD_PRELOAD=/some/path/to/lib/libfoo-${PLATFORM}.so, you will get this error when attempting to run anything:

Cannot open "/some/path/to/lib/libfoo-${PLATFORM}.so"

From browsing the code, this looks to be because the rtld calls _rtld_preload(env['LD_PRELOAD']), which in turn splits the path on ':', and passes the individual paths to _rtld_load_object(), which assumes path expansion has already occurred.

Conversely, when parsing LD_LIBRARY_PATH, _rtld_add_paths() is used, which in turn calls _rtld_expand_path(), which processes these variables.

As a further problem, a workaround where LD_LIBRARY_PATH is set and LD_PRELOAD is assigned a relative path is not possible, as the same process path essentially requires an absolute path in LD_PRELOAD (library paths are not searched).
>How-To-Repeat:
export LD_PRELOAD='/path/to/lib/libfoo-${PLATFORM}.so'
ls

'ls' will fail with 'Cannot open "/path/to/lib/libfoo-${PLATFORM}.so".
>Fix:
Haven't tested it, but I would assume changing _rtld_preload so that it calls _rtld_load_object(_rtld_expand_path(path)) would fix the failure to expand variables. Allowing relative paths would require more involved changes.

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