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From 86eed7ca01864b9fd17099e57f10f2b9b6b568a1 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Bj=C3=B6rn=20Esser?= <besser82@fedoraproject.org>
Date: Mon, 26 Nov 2018 22:33:17 +0100
Subject: [PATCH] pam_unix: Report unusable hashes found by checksalt to
syslog.
libxcrypt can be build-time configured to support (or not support)
various hashing methods. Future versions will also have support for
runtime configuration by the system's vendor and/or administrator.
For that reason adminstrator should be notified by pam if users cannot
log into their account anymore because of such a change in the system's
configuration of libxcrypt.
Also check for malformed hashes, like descrypt hashes starting with
"$2...", which might have been generated by unsafe base64 encoding
functions as used in glibc <= 2.16.
Such hashes are likely to be rejected by many recent implementations
of libcrypt.
* modules/pam_unix/passverify.c (verify_pwd_hash): Report unusable
hashes found by checksalt to syslog.
---
modules/pam_unix/passverify.c | 36 +++++++++++++++++++++++++++++++++++
1 file changed, 36 insertions(+)
diff --git a/modules/pam_unix/passverify.c b/modules/pam_unix/passverify.c
index eb2444bb..2c808eb5 100644
--- a/modules/pam_unix/passverify.c
+++ b/modules/pam_unix/passverify.c
@@ -103,6 +103,42 @@ verify_pwd_hash(const char *p, char *hash, unsigned int nullok)
* Ok, we don't know the crypt algorithm, but maybe
* libcrypt knows about it? We should try it.
*/
+#if defined(CRYPT_CHECKSALT_AVAILABLE) && CRYPT_CHECKSALT_AVAILABLE
+ /* Get the status of the hash from checksalt */
+ int retval_checksalt = crypt_checksalt(hash);
+
+ /*
+ * Check for hashing methods that are disabled by
+ * libcrypt configuration and/or system preset.
+ */
+ if (retval_checksalt == CRYPT_SALT_METHOD_DISABLED) {
+ /*
+ * pam_syslog() needs a pam handle,
+ * but that's not available here.
+ */
+ helper_log_err(LOG_ERR,
+ "pam_unix(verify_pwd_hash): The method "
+ "for computing the hash \"%.6s\" has been "
+ "disabled in libcrypt by the preset from "
+ "the system's vendor and/or administrator.",
+ hash);
+ }
+ /*
+ * Check for malformed hashes, like descrypt hashes
+ * starting with "$2...", which might have been
+ * generated by unsafe base64 encoding functions
+ * as used in glibc <= 2.16.
+ * Such hashes are likely to be rejected by many
+ * recent implementations of libcrypt.
+ */
+ if (retval_checksalt == CRYPT_SALT_INVALID) {
+ helper_log_err(LOG_ERR,
+ "pam_unix(verify_pwd_hash): The hash \"%.6s\""
+ "does not use a method known by the version "
+ "of libcrypt this system is supplied with.",
+ hash);
+ }
+#endif
#ifdef HAVE_CRYPT_R
struct crypt_data *cdata;
cdata = malloc(sizeof(*cdata));
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