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] = '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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