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Message-ID: <20140328104208.GZ8221@example.net>
Date: Fri, 28 Mar 2014 10:42:08 +0000
From: u-igbb@...ey.se
To: musl@...ts.openwall.com
Subject: be able to break inheritance of LD_LIBRARY_PATH
Hello,
I was aware of musl for some time and now consider deploying it as
a default library for new software builds, due to its very appealing
virtues.
Yet there is a small but important issue.
For our software setup it is crucial (quite useful otherwise in general)
to be able to specify the location of the dynamic libraries per binary/run
_without_ the unconditional inheritance imposed by LD_LIBRARY_PATH.
A very nice solution would be the ability to explicitely run a standalone
dynamic loader, as implemented in both glibc and uclibc. We are heavily
relying on this functionality.
I do not know how hard it would be to teach the musl loader
to be runnable standalone and which corner cases this might create.
As a simpler approach I might suggest simply being able to drop
LD_LIBRARY_PATH as soon as it has been read. An extra environment
variable as a flag would do.
Compared to a standalone loader this lacks the ability to run
a binary with a different version of the loader/musl but at least
makes it straightforward and safe to freely specify where to find other
libraries.
A naïve implementation might look as follows:
--- src/ldso/dynlink.c.ori 2014-03-28 10:37:34.821317811 +0100
+++ src/ldso/dynlink.c 2014-03-28 11:21:16.828047766 +0100
@@ -962,6 +962,7 @@
size_t vdso_base;
size_t *auxv;
char **envp = argv+argc+1;
+ int forget_ld_library_path = 0;
/* Find aux vector just past environ[] */
for (i=argc+1; argv[i]; i++)
@@ -969,8 +970,19 @@
env_path = argv[i]+16;
else if (!memcmp(argv[i], "LD_PRELOAD=", 11))
env_preload = argv[i]+11;
+ else if (!memcmp(argv[i], "FORGET_LD_LIBRARY_PATH=", 23))
+ forget_ld_library_path = 1;
auxv = (void *)(argv+i+1);
+ /* one _may_ wish to break the inheritance of LD_LIBRARY_PATH,
+ * the hack below only works if the corresponding memory is writable
+ * -- rl */
+ if (forget_ld_library_path)
+ for (i=argc+1; argv[i]; i++)
+ if (!memcmp(argv[i], "LD_LIBRARY_PATH=", 16) ||
+ !memcmp(argv[i], "FORGET_LD_LIBRARY_PATH=", 23))
+ argv[i][0] = 'X';
+
decode_vec(auxv, aux, AUX_CNT);
/* Only trust user/env if kernel says we're not suid/sgid */
What do you think about this? Can this or something better be done?
I would love to be able to go with musl.
Regards,
Rune
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