From 4f95ab1f8110a8ab9d7b0e192731ce467f6e5c26 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Janne=20He=C3=9F?= <janne@hess.ooo>
Date: Sun, 4 Sep 2022 11:15:02 -0600
Subject: [PATCH] Allow loading token handlers from the default search path
Since [1] landed in cryptsetup, token handlers (libcryptsetup-token-*.so)
are loaded from a fixed path defined at compile-time. This is
problematic with NixOS since it introduces a dependency cycle
between cryptsetup and systemd.
This downstream patch [2] allows loading token plugins from the
default library search path. This approach is not accepted upstream [3]
due to security concerns, but the potential attack vectors require
root access and they are sufficiently addressed:
* cryptsetup could be used as a setuid binary (not used in NixOS).
In this case, LD_LIBRARY_PATH is ignored because of secure-execution
mode.
* cryptsetup running as root could lead to a malicious token handler
being loaded through LD_LIBRARY_PATH. However, fixing the path
doesn't prevent the same malicious .so being loaded through LD_PRELOAD.
[1] https://gitlab.com/cryptsetup/cryptsetup/-/commit/5b9e98f94178d3cd179d9f6e2a0a68c7d9eb6507
[2] https://github.com/NixOS/nixpkgs/issues/167994#issuecomment-1094249369
[3] https://gitlab.com/cryptsetup/cryptsetup/-/issues/733
---
lib/luks2/luks2_token.c | 4 +---
1 file changed, 1 insertion(+), 3 deletions(-)
diff --git a/lib/luks2/luks2_token.c b/lib/luks2/luks2_token.c
index 26467253..6f8329f0 100644
--- a/lib/luks2/luks2_token.c
+++ b/lib/luks2/luks2_token.c
@@ -151,12 +151,10 @@ crypt_token_load_external(struct crypt_device *cd, const char *name, struct cryp
token = &ret->u.v2;
- r = snprintf(buf, sizeof(buf), "%s/libcryptsetup-token-%s.so", crypt_token_external_path(), name);
+ r = snprintf(buf, sizeof(buf), "libcryptsetup-token-%s.so", name);
if (r < 0 || (size_t)r >= sizeof(buf))
return -EINVAL;
- assert(*buf == '/');
-
log_dbg(cd, "Trying to load %s.", buf);
h = dlopen(buf, RTLD_LAZY);
--
2.37.2