NetCube-Systems-Austria/kumquat-buildroot
1
0
Fork 0
Code Issues Pull Requests Actions Packages Projects Releases Wiki Activity

package/libpam-tacplus: fix CVE-2020-27743

Browse Source 
libtac in pam_tacplus through 1.5.1 lacks a check for a failure of
RAND_bytes()/RAND_pseudo_bytes(). This could lead to use of a
non-random/predictable session_id.

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
This commit is contained in:
Fabrice Fontaine 2020-10-28 09:26:58 +01:00 committed by Thomas Petazzoni
parent ef4f72aef7
commit 70499767e5
2 changed files with 149 additions and 0 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

146
package/libpam-tacplus/0005-Check-for-failure-of-OpenSSL-RAND_pseudo_bytes.patch Normal file
View File

@ -0,0 +1,146 @@
From c9bed7496e81e550ee22746f23bbb11be2e046ed Mon Sep 17 00:00:00 2001
From: Duncan Eastoe <duncan.eastoe@att.com>
Date: Thu, 22 Oct 2020 19:18:27 +0100
Subject: [PATCH] magic.c: check for failure of RAND_[pseudo_]bytes
When magic() is implemented via libcrypto's RAND_bytes or
RAND_pseudo_bytes we should check for a failure and abort to
ensure we don't use a predictable session_id.
This prevents (further) weakening* of the TACACS+ protocol
"encryption" since session_id is an input to the algorithm.
*by modern standards TACACS+ is deemed "obfuscated" - RFC 8907.
[Retrieved from:
https://github.com/kravietz/pam_tacplus/commit/468cc9d484364ecdc8bb245805f5c1fcb415fec9]
Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
---
libtac/lib/magic.c | 26 +++++++++++++++++++++-----
pam_tacplus.c | 6 ++++++
2 files changed, 27 insertions(+), 5 deletions(-)
diff --git a/libtac/lib/magic.c b/libtac/lib/magic.c
index e13a483..ae6b44f 100644
--- a/libtac/lib/magic.c
+++ b/libtac/lib/magic.c
@@ -81,26 +81,42 @@ magic()
#elif defined(HAVE_OPENSSL_RAND_H) && defined(HAVE_LIBCRYPTO)
+#include <openssl/err.h>
#include <openssl/rand.h>
/* RAND_bytes is OpenSSL's classic function to obtain cryptographic strength pseudo-random bytes
- however, since the magic() function is used to generate TACACS+ session id rather than crypto keys
- we can use RAND_pseudo_bytes() which doesn't deplete the system's entropy pool
+ however, we can use RAND_pseudo_bytes() which doesn't deplete the system's entropy pool, so long
+ as it returns a "cryptographically strong" result - since session_id is an input to the TACACS+
+ "encryption" ("obfuscation" by modern standards - RFC 8907) algorithm.
*/
u_int32_t
magic()
{
u_int32_t num;
+ int ret;
#ifdef HAVE_RAND_BYTES
- RAND_bytes((unsigned char *)&num, sizeof(num));
+ ret = RAND_bytes((unsigned char *)&num, sizeof(num));
#elif HAVE_RAND_PSEUDO_BYTES
- RAND_pseudo_bytes((unsigned char *)&num, sizeof(num));
+ ret = RAND_pseudo_bytes((unsigned char *)&num, sizeof(num));
#else
#error Neither RAND_bytes nor RAND_pseudo_bytes seems to be available
#endif
- return num;
+
+ /* RAND_bytes success / RAND_pseudo_bytes "cryptographically strong" result */
+ if (ret == 1)
+ return num;
+
+ TACSYSLOG(LOG_CRIT,"%s: "
+#ifdef HAVE_RAND_BYTES
+ "RAND_bytes "
+#else
+ "RAND_pseudo_bytes "
+#endif
+ "failed; ret: %d err: %ld", __FUNCTION__, ret, ERR_get_error());
+
+ exit(1);
}
#else
diff --git a/pam_tacplus.c b/pam_tacplus.c
index a0cb83d..4999ca9 100644
--- a/pam_tacplus.c
+++ b/pam_tacplus.c
@@ -718,6 +718,12 @@ int pam_sm_acct_mgmt(pam_handle_t *pamh, int UNUSED(flags), int argc,
PAM_EXTERN
int pam_sm_open_session(pam_handle_t *pamh, int UNUSED(flags), int argc,
const char **argv) {
+
+/* Task ID has no need to be cryptographically strong so we don't
+ * check for failures of the RAND functions. If they fail then we are
+ * as well sending the accounting request regardless of whether any value
+ * was written to task_id.
+ */
#if defined(HAVE_OPENSSL_RAND_H) && defined(HAVE_LIBCRYPTO)
# if defined(HAVE_RAND_BYTES)
RAND_bytes((unsigned char *) &task_id, sizeof(task_id));
From bceaab0cd51a09b88f40f19da799ac7390264bf8 Mon Sep 17 00:00:00 2001
From: Duncan Eastoe <duncan.eastoe@att.com>
Date: Fri, 23 Oct 2020 11:23:07 +0100
Subject: [PATCH 2/2] pam_tacplus.c: Fallback to using PID as task ID
If there is a failure obtaining a random task ID for the session
accounting request then fallback to using the PID, as this is unique
for the lifetime of the PAM application and therefore session.
---
pam_tacplus.c | 16 ++++++++++++----
1 file changed, 12 insertions(+), 4 deletions(-)
diff --git a/pam_tacplus.c b/pam_tacplus.c
index 4999ca9..b69e3d0 100644
--- a/pam_tacplus.c
+++ b/pam_tacplus.c
@@ -100,8 +100,13 @@ int _pam_send_account(int tac_fd, int type, const char *user, char *tty,
} else if (type == TAC_PLUS_ACCT_FLAG_STOP) {
tac_add_attrib(&attr, "stop_time", buf);
}
- sprintf(buf, "%hu", task_id);
+
+ if (task_id == 0)
+ snprintf(buf, sizeof(buf), "%d", getpid());
+ else
+ snprintf(buf, sizeof(buf), "%hu", task_id);
tac_add_attrib(&attr, "task_id", buf);
+
tac_add_attrib(&attr, "service", tac_service);
if (tac_protocol[0] != '\0')
tac_add_attrib(&attr, "protocol", tac_protocol);
@@ -720,9 +725,8 @@ int pam_sm_open_session(pam_handle_t *pamh, int UNUSED(flags), int argc,
const char **argv) {
/* Task ID has no need to be cryptographically strong so we don't
- * check for failures of the RAND functions. If they fail then we are
- * as well sending the accounting request regardless of whether any value
- * was written to task_id.
+ * check for failures of the RAND functions. If we fail to get an ID we
+ * fallback to using our PID (in _pam_send_account).
*/
#if defined(HAVE_OPENSSL_RAND_H) && defined(HAVE_LIBCRYPTO)
# if defined(HAVE_RAND_BYTES)
@@ -734,6 +738,10 @@ int pam_sm_open_session(pam_handle_t *pamh, int UNUSED(flags), int argc,
task_id=(short int) magic();
#endif
+ if (task_id == 0)
+ syslog(LOG_INFO, "%s: failed to generate random task ID, "
+ "falling back to PID", __FUNCTION__);
+
return _pam_account(pamh, argc, argv, TAC_PLUS_ACCT_FLAG_START, NULL);
} /* pam_sm_open_session */

3
package/libpam-tacplus/libpam-tacplus.mk
View File

@ -17,4 +17,7 @@ LIBPAM_TACPLUS_INSTALL_STAGING = YES
LIBPAM_TACPLUS_CONF_ENV = \
ax_cv_check_cflags___fstack_protector_all=$(if $(BR2_TOOLCHAIN_HAS_SSP),yes,no)
# 0005-Check-for-failure-of-OpenSSL-RAND_pseudo_bytes.patch
LIBPAM_TACPLUS_IGNORE_CVES += CVE-2020-27743
$(eval $(autotools-package))