TACACS: Don't send sshd's bad password to AAA

src/tacacs/pam/0007-handle-bad-password-set-by-sshd.patch

@@ -0,0 +1,133 @@
+From f2687e7a442c83e19190695021fb9a60fe07ba60 Mon Sep 17 00:00:00 2001
+From: Renuka Manavalan <[email protected]>
+Date: Wed, 17 Nov 2021 02:31:45 +0000
+Subject: [PATCH] handle bad password set by sshd
+
+---
+ pam_tacplus.c | 11 +++++++++--
+ support.c     | 37 +++++++++++++++++++++++++++++++++++++
+ support.h     |  1 +
+ tacc.c        |  4 ++--
+ 4 files changed, 49 insertions(+), 4 deletions(-)
+
+diff --git a/pam_tacplus.c b/pam_tacplus.c
+index ec8ea27..014421b 100644
+--- a/pam_tacplus.c
++++ b/pam_tacplus.c
+@@ -251,6 +251,13 @@ int pam_sm_authenticate (pam_handle_t * pamh, int flags,
+         return PAM_CRED_INSUFFICIENT;
+     }
+
++    if (validate_not_sshd_bad_pass(pass) != PAM_SUCCESS) {
++        syslog(LOG_ERR, "auth fail: Password incorrect");
++        memset(pass, 0, strlen (pass));
++        free(pass);
++        return PAM_AUTH_ERR;
++    }
++
+     retval = pam_set_item (pamh, PAM_AUTHTOK, pass);
+     if (retval != PAM_SUCCESS) {
+         _pam_log(LOG_ERR, "unable to set password");
+@@ -483,7 +490,7 @@ int pam_sm_authenticate (pam_handle_t * pamh, int flags,
+         syslog(LOG_DEBUG, "%s: exit with pam status: %d", __FUNCTION__, status);
+
+     if (NULL != pass) {
+-        bzero(pass, strlen (pass));
++        memset(pass, 0, strlen (pass));
+         free(pass);
+         pass = NULL;
+     }
+@@ -979,7 +986,7 @@ finish:
+         syslog(LOG_DEBUG, "%s: exit with pam status: %d", __FUNCTION__, status);
+
+     if (NULL != pass) {
+-        bzero(pass, strlen(pass));
++        memset(pass, 0, strlen (pass));
+         free(pass);
+         pass = NULL;
+     }
+diff --git a/support.c b/support.c
+index 3e55e2f..09d09bf 100644
+--- a/support.c
++++ b/support.c
+@@ -108,6 +108,43 @@ int converse(pam_handle_t * pamh, int nargs, const struct pam_message *message,
+     return retval;
+ }
+
++/*
++ * Ref: From <https://groups.google.com/g/mailing.unix.openssh-dev/c/ViHvtciKYh0>
++ * For future archive searchers:
++ * > Why does OpenSSH replaces the password entered by the user with the
++ * > bad password - "\b\n\r\177INCORRECT
++ *
++ * There are some situations where sshd determines a user can't log in.
++ * Typical samples of that are DenyUsers or PermitRootLogin.
++ * In those cases sshd *still* calls PAM, so that delays set by it are
++ * still performed to the user (without leaking info about accounts
++ * existing, disabled, etc.). But in order to ensure it can't succeed,
++ * replaces the password with that impossible one.
++ *
++ */
++int validate_not_sshd_bad_pass(const char *pass)
++{
++    const char *SSHD_BAD_PASS = "\010\012\015\177INCORRECT";
++    const int SSHD_BAD_PASS_LEN = strlen(SSHD_BAD_PASS);
++
++    int len = strlen(pass);
++    const char *p = pass;
++
++    if (len == 0)
++        return PAM_SUCCESS;
++
++    while (len > 0) {
++        int l = len < SSHD_BAD_PASS_LEN ? len : SSHD_BAD_PASS_LEN;
++
++        if (strncmp(p, SSHD_BAD_PASS, l) != 0)
++            return PAM_SUCCESS;
++
++        len -= l;
++        p += l;
++    }
++    return PAM_AUTH_ERR;
++}
++
+ /* stolen from pam_stress */
+ int tacacs_get_password (pam_handle_t * pamh, int flags
+     ,int ctrl, char **password) {
+diff --git a/support.h b/support.h
+index 09b8a85..cb04a4f 100644
+--- a/support.h
++++ b/support.h
+@@ -42,6 +42,7 @@ extern struct addrinfo *tac_source_addr;
+ int _pam_parse (int, const char **);
+ unsigned long _resolve_name (char *);
+ unsigned long _getserveraddr (char *serv);
++int validate_not_sshd_bad_pass(const char *pass);
+ int tacacs_get_password (pam_handle_t *, int, int, char **);
+ int converse (pam_handle_t *, int, const struct pam_message *, struct pam_response **);
+ void _pam_log (int, const char *, ...);
+diff --git a/tacc.c b/tacc.c
+index fcc7d8c..bf0f2a3 100644
+--- a/tacc.c
++++ b/tacc.c
+@@ -181,7 +181,7 @@ int main(int argc, char **argv) {
+ 				break;
+ 			case 'L':
+ 				// tac_login is a global variable initialized in libtac
+-				bzero(tac_login, sizeof(tac_login));
++				memset(tac_login, 0, sizeof(tac_login));
+ 				strncpy(tac_login, optarg, sizeof(tac_login) - 1);
+ 				break;
+ 			case 'p':
+@@ -312,7 +312,7 @@ int main(int argc, char **argv) {
+ 	}
+
+ 	/* we no longer need the password in our address space */
+-	bzero(pass, strlen(pass));
++	memset(pass, 0, strlen(pass));
+ 	pass = NULL;
+
+ 	if (do_account) {
+-- 
+2.17.1
+

src/tacacs/pam/Makefile

@@ -20,6 +20,7 @@ $(addprefix $(DEST)/, $(MAIN_TARGET)): $(DEST)/% :
 	git apply ../0004-management-vrf-support.patch
 	git apply ../0005-pam-Modify-parsing-of-IP-address-and-port-number-to-.patch
 	git apply ../0006-Add-support-for-source-ip-address.patch
+	git apply ../0007-handle-bad-password-set-by-sshd.patch
 
 	dpkg-buildpackage -rfakeroot -b -us -uc -j$(SONIC_CONFIG_MAKE_JOBS) --admindir $(SONIC_DPKG_ADMINDIR)
 	popd