[patch] Makes KCM: work for openssh

0001-Description-Improve-ccache-handling-in-openssh.patch (text/plain), 19.16 KB, created by Joakim Tjernlund on 2023-11-10 17:01:25 UTC

From 446bfc80ade4b21915adbf5e5f8006fba2b3cfa2 Mon Sep 17 00:00:00 2001
From: Joakim Tjernlund <[e-mail]>
Date: Fri, 10 Nov 2023 17:07:42 +0100
Subject: [PATCH] Description: Improve ccache handling in openssh

Bug: https://bugzilla.mindrot.org/show_bug.cgi?id=2775
Origin: vendor, https://src.fedoraproject.org/rpms/openssh/blob/rawhide/f/openssh-7.7p1-gssapi-new-unique.patch(rawhide branch is currently at commit ebc2a70d)
Author: Jakub Jelen <[e-mail]>
Last-Updated: 2023-01-09
Forwarded: no
---
 auth-krb5.c     | 261 ++++++++++++++++++++++++++++++++++++++++++------
 auth.h          |   3 +-
 gss-serv-krb5.c |  40 ++++----
 gss-serv.c      |   6 +-
 servconf.c      |  12 ++-
 servconf.h      |   2 +
 session.c       |   5 +-
 ssh-gss.h       |   4 +-
 sshd.c          |   2 +-
 sshd_config.5   |   8 ++
 10 files changed, 284 insertions(+), 59 deletions(-)

diff --git a/auth-krb5.c b/auth-krb5.c
index c99e4e4..61ef882 100644
--- a/auth-krb5.c
+++ b/auth-krb5.c
@@ -51,6 +51,7 @@
 #include <unistd.h>
 #include <string.h>
 #include <krb5.h>
+#include <profile.h>
 
 extern ServerOptions	 options;
 
@@ -77,7 +78,7 @@ auth_krb5_password(Authctxt *authctxt, const char *password)
 #endif
 	krb5_error_code problem;
 	krb5_ccache ccache = NULL;
-	int len;
+	char *ticket_name = NULL;
 	char *client, *platform_client;
 	const char *errmsg;
 
@@ -163,8 +164,8 @@ auth_krb5_password(Authctxt *authctxt, const char *password)
 		goto out;
 	}
 
-	problem = ssh_krb5_cc_gen(authctxt->krb5_ctx,
-	    &authctxt->krb5_fwd_ccache);
+	problem = ssh_krb5_cc_new_unique(authctxt->krb5_ctx,
+	     &authctxt->krb5_fwd_ccache, &authctxt->krb5_set_env);
 	if (problem)
 		goto out;
 
@@ -179,15 +180,14 @@ auth_krb5_password(Authctxt *authctxt, const char *password)
 		goto out;
 #endif
 
-	authctxt->krb5_ticket_file = (char *)krb5_cc_get_name(authctxt->krb5_ctx, authctxt->krb5_fwd_ccache);
+	problem = krb5_cc_get_full_name(authctxt->krb5_ctx,
+	    authctxt->krb5_fwd_ccache, &ticket_name);
 
-	len = strlen(authctxt->krb5_ticket_file) + 6;
-	authctxt->krb5_ccname = xmalloc(len);
-	snprintf(authctxt->krb5_ccname, len, "FILE:%s",
-	    authctxt->krb5_ticket_file);
+	authctxt->krb5_ccname = xstrdup(ticket_name);
+	krb5_free_string(authctxt->krb5_ctx, ticket_name);
 
 #ifdef USE_PAM
-	if (options.use_pam)
+	if (options.use_pam && authctxt->krb5_set_env)
 		do_pam_putenv("KRB5CCNAME", authctxt->krb5_ccname);
 #endif
 
@@ -223,11 +223,54 @@ auth_krb5_password(Authctxt *authctxt, const char *password)
 void
 krb5_cleanup_proc(Authctxt *authctxt)
 {
+	struct stat krb5_ccname_stat;
+	char krb5_ccname[128], *krb5_ccname_dir_start, *krb5_ccname_dir_end;
+
 	debug("krb5_cleanup_proc called");
 	if (authctxt->krb5_fwd_ccache) {
-		krb5_cc_destroy(authctxt->krb5_ctx, authctxt->krb5_fwd_ccache);
+		krb5_context ctx = authctxt->krb5_ctx;
+		krb5_cccol_cursor cursor;
+		krb5_ccache ccache;
+		int ret;
+
+		krb5_cc_destroy(ctx, authctxt->krb5_fwd_ccache);
 		authctxt->krb5_fwd_ccache = NULL;
+
+		ret = krb5_cccol_cursor_new(ctx, &cursor);
+		if (ret)
+			goto out;
+
+		ret = krb5_cccol_cursor_next(ctx, cursor, &ccache);
+		if (ret == 0 && ccache != NULL) {
+			/* There is at least one other ccache in collection
+			 * we can switch to */
+			krb5_cc_switch(ctx, ccache);
+		} else if (authctxt->krb5_ccname != NULL) {
+			/* Clean up the collection too */
+			strncpy(krb5_ccname, authctxt->krb5_ccname, sizeof(krb5_ccname) - 10);
+			krb5_ccname_dir_start = strchr(krb5_ccname, ':') + 1;
+			*krb5_ccname_dir_start++ = '\0';
+			if (strcmp(krb5_ccname, "DIR") == 0) {
+
+				strcat(krb5_ccname_dir_start, "/primary");
+
+				if (stat(krb5_ccname_dir_start, &krb5_ccname_stat) == 0) {
+					if (unlink(krb5_ccname_dir_start) == 0) {
+						krb5_ccname_dir_end = strrchr(krb5_ccname_dir_start, '/');
+						*krb5_ccname_dir_end = '\0';
+						if (rmdir(krb5_ccname_dir_start) == -1)
+							debug("cache dir '%s' remove failed: %s",
+							    krb5_ccname_dir_start, strerror(errno));
+					}
+					else
+						debug("cache primary file '%s', remove failed: %s",
+						    krb5_ccname_dir_start, strerror(errno));
+				}
+			}
+		}
+		krb5_cccol_cursor_free(ctx, &cursor);
 	}
+out:
 	if (authctxt->krb5_user) {
 		krb5_free_principal(authctxt->krb5_ctx, authctxt->krb5_user);
 		authctxt->krb5_user = NULL;
@@ -238,36 +281,188 @@ krb5_cleanup_proc(Authctxt *authctxt)
 	}
 }
 
-#ifndef HEIMDAL
-krb5_error_code
-ssh_krb5_cc_gen(krb5_context ctx, krb5_ccache *ccache) {
-	int tmpfd, ret, oerrno;
-	char ccname[40];
-	mode_t old_umask;
 
-	ret = snprintf(ccname, sizeof(ccname),
-	    "FILE:/tmp/krb5cc_%d_XXXXXXXXXX", geteuid());
-	if (ret < 0 || (size_t)ret >= sizeof(ccname))
-		return ENOMEM;
-
-	old_umask = umask(0177);
-	tmpfd = mkstemp(ccname + strlen("FILE:"));
-	oerrno = errno;
-	umask(old_umask);
-	if (tmpfd == -1) {
-		logit("mkstemp(): %.100s", strerror(oerrno));
-		return oerrno;
+#if !defined(HEIMDAL)
+int
+ssh_asprintf_append(char **dsc, const char *fmt, ...) {
+	char *src, *old;
+	va_list ap;
+	int i;
+
+	va_start(ap, fmt);
+	i = vasprintf(&src, fmt, ap);
+	va_end(ap);
+
+	if (i == -1 || src == NULL)
+		return -1;
+
+	old = *dsc;
+
+	i = asprintf(dsc, "%s%s", *dsc, src);
+	if (i == -1 || src == NULL) {
+		free(src);
+		return -1;
+	}
+
+	free(old);
+	free(src);
+
+	return i;
+}
+
+int
+ssh_krb5_expand_template(char **result, const char *template) {
+	char *p_n, *p_o, *r, *tmp_template;
+
+	debug3_f("called, template = %s", template);
+	if (template == NULL)
+		return -1;
+
+	tmp_template = p_n = p_o = xstrdup(template);
+	r = xstrdup("");
+
+	while ((p_n = strstr(p_o, "%{")) != NULL) {
+
+		*p_n++ = '\0';
+		if (ssh_asprintf_append(&r, "%s", p_o) == -1)
+			goto cleanup;
+
+		if (strncmp(p_n, "{uid}", 5) == 0 || strncmp(p_n, "{euid}", 6) == 0 ||
+			strncmp(p_n, "{USERID}", 8) == 0) {
+			p_o = strchr(p_n, '}') + 1;
+			if (ssh_asprintf_append(&r, "%d", geteuid()) == -1)
+				goto cleanup;
+			continue;
+		}
+		else if (strncmp(p_n, "{TEMP}", 6) == 0) {
+			p_o = strchr(p_n, '}') + 1;
+			if (ssh_asprintf_append(&r, "/tmp") == -1)
+				goto cleanup;
+			continue;
+		} else {
+			p_o = strchr(p_n, '}') + 1;
+			*p_o = '\0';
+			debug_f("unsupported token %s in %s", p_n, template);
+			/* unknown token, fallback to the default */
+			goto cleanup;
+		}
 	}
 
-	if (fchmod(tmpfd,S_IRUSR | S_IWUSR) == -1) {
+	if (ssh_asprintf_append(&r, "%s", p_o) == -1)
+		goto cleanup;
+
+	*result = r;
+	free(tmp_template);
+	return 0;
+
+cleanup:
+	free(r);
+	free(tmp_template);
+	return -1;
+}
+
+krb5_error_code
+ssh_krb5_get_cctemplate(krb5_context ctx, char **ccname) {
+	profile_t p;
+	int ret = 0;
+	char *value = NULL;
+
+	debug3_f("called");
+	ret = krb5_get_profile(ctx, &p);
+	if (ret)
+		return ret;
+
+	ret = profile_get_string(p, "libdefaults", "default_ccache_name", NULL, NULL, &value);
+	if (ret || !value)
+		return ret;
+
+	ret = ssh_krb5_expand_template(ccname, value);
+
+	debug3_f("returning with ccname = %s", *ccname);
+	return ret;
+}
+
+krb5_error_code
+ssh_krb5_cc_new_unique(krb5_context ctx, krb5_ccache *ccache, int *need_environment) {
+	int tmpfd, ret, oerrno, type_len;
+	char *ccname = NULL;
+	mode_t old_umask;
+	char *type = NULL, *colon = NULL;
+
+	debug3_f("called");
+	if (need_environment)
+		*need_environment = 0;
+	ret = ssh_krb5_get_cctemplate(ctx, &ccname);
+	if (ret || !ccname || options.kerberos_unique_ccache) {
+		/* Otherwise, go with the old method */
+		if (ccname)
+			free(ccname);
+		ccname = NULL;
+
+		ret = asprintf(&ccname,
+		    "FILE:/tmp/krb5cc_%d_XXXXXXXXXX", geteuid());
+		if (ret < 0)
+			return ENOMEM;
+
+		old_umask = umask(0177);
+		tmpfd = mkstemp(ccname + strlen("FILE:"));
 		oerrno = errno;
-		logit("fchmod(): %.100s", strerror(oerrno));
+		umask(old_umask);
+		if (tmpfd == -1) {
+			logit("mkstemp(): %.100s", strerror(oerrno));
+			return oerrno;
+		}
+
+		if (fchmod(tmpfd,S_IRUSR | S_IWUSR) == -1) {
+			oerrno = errno;
+			logit("fchmod(): %.100s", strerror(oerrno));
+			close(tmpfd);
+			return oerrno;
+		}
+		/* make sure the KRB5CCNAME is set for non-standard location */
+		if (need_environment)
+			*need_environment = 1;
 		close(tmpfd);
-		return oerrno;
 	}
-	close(tmpfd);
 
-	return (krb5_cc_resolve(ctx, ccname, ccache));
+	debug3_f("setting default ccname to %s", ccname);
+	/* set the default with already expanded user IDs */
+	ret = krb5_cc_set_default_name(ctx, ccname);
+	if (ret)
+		return ret;
+
+	if ((colon = strstr(ccname, ":")) != NULL) {
+		type_len = colon - ccname;
+		type = malloc((type_len + 1) * sizeof(char));
+		if (type == NULL)
+			return ENOMEM;
+		strncpy(type, ccname, type_len);
+		type[type_len] = 0;
+	} else {
+		type = strdup(ccname);
+	}
+
+	/* If we have a credential cache from krb5.conf, we need to switch
+	 * a primary cache for this collection, if it supports that (non-FILE)
+	 */
+	if (krb5_cc_support_switch(ctx, type)) {
+		debug3_f("calling cc_new_unique(%s)", ccname);
+		ret = krb5_cc_new_unique(ctx, type, NULL, ccache);
+		free(type);
+		if (ret)
+			return ret;
+
+		debug3_f("calling cc_switch()");
+		return krb5_cc_switch(ctx, *ccache);
+	} else {
+		/* Otherwise, we can not create a unique ccname here (either
+		 * it is already unique from above or the type does not support
+		 * collections
+		 */
+		free(type);
+		debug3_f("calling cc_resolve(%s)", ccname);
+		return (krb5_cc_resolve(ctx, ccname, ccache));
+	}
 }
 #endif /* !HEIMDAL */
 #endif /* KRB5 */
diff --git a/auth.h b/auth.h
index 6d2d397..8a8bd43 100644
--- a/auth.h
+++ b/auth.h
@@ -82,6 +82,7 @@ struct Authctxt {
 	krb5_principal	 krb5_user;
 	char		*krb5_ticket_file;
 	char		*krb5_ccname;
+	int		 krb5_set_env;
 #endif
 	struct sshbuf	*loginmsg;
 
@@ -241,7 +242,7 @@ FILE	*auth_openprincipals(const char *, struct passwd *, int);
 int	 sys_auth_passwd(struct ssh *, const char *);
 
 #if defined(KRB5) && !defined(HEIMDAL)
-krb5_error_code ssh_krb5_cc_gen(krb5_context, krb5_ccache *);
+krb5_error_code ssh_krb5_cc_new_unique(krb5_context, krb5_ccache *, int *);
 #endif
 
 #endif /* AUTH_H */
diff --git a/gss-serv-krb5.c b/gss-serv-krb5.c
index a151bc1..9a21dbf 100644
--- a/gss-serv-krb5.c
+++ b/gss-serv-krb5.c
@@ -113,7 +113,7 @@ ssh_gssapi_krb5_userok(ssh_gssapi_client *client, char *name)
 /* This writes out any forwarded credentials from the structure populated
  * during userauth. Called after we have setuid to the user */
 
-static void
+static int
 ssh_gssapi_krb5_storecreds(ssh_gssapi_client *client)
 {
 	krb5_ccache ccache;
@@ -121,15 +121,17 @@ ssh_gssapi_krb5_storecreds(ssh_gssapi_client *client)
 	krb5_principal princ;
 	OM_uint32 maj_status, min_status;
 	int len;
+	const char *new_ccname, *new_cctype;
 	const char *errmsg;
+	int set_env = 0;
 
 	if (client->creds == NULL) {
 		debug("No credentials stored");
-		return;
+		return 0;
 	}
 
 	if (ssh_gssapi_krb5_init() == 0)
-		return;
+		return 0;
 
 #ifdef HEIMDAL
 # ifdef HAVE_KRB5_CC_NEW_UNIQUE
@@ -143,14 +145,14 @@ ssh_gssapi_krb5_storecreds(ssh_gssapi_client *client)
 		krb5_get_err_text(krb_context, problem));
 # endif
 		krb5_free_error_message(krb_context, errmsg);
-		return;
+		return 0;
 	}
 #else
-	if ((problem = ssh_krb5_cc_gen(krb_context, &ccache))) {
+	if ((problem = ssh_krb5_cc_new_unique(krb_context, &ccache, &set_env)) != 0) {
 		errmsg = krb5_get_error_message(krb_context, problem);
-		logit("ssh_krb5_cc_gen(): %.100s", errmsg);
+		logit("ssh_krb5_cc_new_unique(): %.100s", errmsg);
 		krb5_free_error_message(krb_context, errmsg);
-		return;
+		return 0;
 	}
 #endif	/* #ifdef HEIMDAL */
 
@@ -159,7 +161,7 @@ ssh_gssapi_krb5_storecreds(ssh_gssapi_client *client)
 		errmsg = krb5_get_error_message(krb_context, problem);
 		logit("krb5_parse_name(): %.100s", errmsg);
 		krb5_free_error_message(krb_context, errmsg);
-		return;
+		return 0;
 	}
 
 	if ((problem = krb5_cc_initialize(krb_context, ccache, princ))) {
@@ -168,7 +170,7 @@ ssh_gssapi_krb5_storecreds(ssh_gssapi_client *client)
 		krb5_free_error_message(krb_context, errmsg);
 		krb5_free_principal(krb_context, princ);
 		krb5_cc_destroy(krb_context, ccache);
-		return;
+		return 0;
 	}
 
 	krb5_free_principal(krb_context, princ);
@@ -177,23 +179,27 @@ ssh_gssapi_krb5_storecreds(ssh_gssapi_client *client)
 	    client->creds, ccache))) {
 		logit("gss_krb5_copy_ccache() failed");
 		krb5_cc_destroy(krb_context, ccache);
-		return;
+		return 0;
 	}
+	new_cctype = krb5_cc_get_type(krb_context, ccache);
+	new_ccname = krb5_cc_get_name(krb_context, ccache);
 
-	client->store.filename = xstrdup(krb5_cc_get_name(krb_context, ccache));
-	client->store.envvar = "KRB5CCNAME";
-	len = strlen(client->store.filename) + 6;
-	client->store.envval = xmalloc(len);
-	snprintf(client->store.envval, len, "FILE:%s", client->store.filename);
+	xasprintf(&client->store.envval, "%s:%s", new_cctype, new_ccname);
+
+	if (set_env) {
+		client->store.envvar = "KRB5CCNAME";
+	}
+	if ((strcmp(new_cctype, "FILE") == 0) || (strcmp(new_cctype, "DIR") == 0))
+		client->store.filename = xstrdup(new_ccname);
 
 #ifdef USE_PAM
-	if (options.use_pam)
+	if (options.use_pam && set_env)
 		do_pam_putenv(client->store.envvar, client->store.envval);
 #endif
 
 	krb5_cc_close(krb_context, ccache);
 
-	return;
+	return set_env;
 }
 
 ssh_gssapi_mech gssapi_kerberos_mech = {
diff --git a/gss-serv.c b/gss-serv.c
index 00e3d11..4a18c82 100644
--- a/gss-serv.c
+++ b/gss-serv.c
@@ -328,13 +328,15 @@ ssh_gssapi_cleanup_creds(void)
 }
 
 /* As user */
-void
+int
 ssh_gssapi_storecreds(void)
 {
 	if (gssapi_client.mech && gssapi_client.mech->storecreds) {
-		(*gssapi_client.mech->storecreds)(&gssapi_client);
+		return (*gssapi_client.mech->storecreds)(&gssapi_client);
 	} else
 		debug("ssh_gssapi_storecreds: Not a GSSAPI mechanism");
+
+	return 0;
 }
 
 /* This allows GSSAPI methods to do things to the child's environment based
diff --git a/servconf.c b/servconf.c
index 45a2f2c..8b9835f 100644
--- a/servconf.c
+++ b/servconf.c
@@ -133,6 +133,7 @@ initialize_server_options(ServerOptions *options)
 	options->kerberos_or_local_passwd = -1;
 	options->kerberos_ticket_cleanup = -1;
 	options->kerberos_get_afs_token = -1;
+	options->kerberos_unique_ccache = -1;
 	options->gss_authentication=-1;
 	options->gss_cleanup_creds = -1;
 	options->gss_strict_acceptor = -1;
@@ -356,6 +357,8 @@ fill_default_server_options(ServerOptions *options)
 		options->kerberos_ticket_cleanup = 1;
 	if (options->kerberos_get_afs_token == -1)
 		options->kerberos_get_afs_token = 0;
+	if (options->kerberos_unique_ccache == -1)
+		options->kerberos_unique_ccache = 0;
 	if (options->gss_authentication == -1)
 		options->gss_authentication = 0;
 	if (options->gss_cleanup_creds == -1)
@@ -503,7 +506,7 @@ typedef enum {
 	sPort, sHostKeyFile, sLoginGraceTime,
 	sPermitRootLogin, sLogFacility, sLogLevel, sLogVerbose,
 	sKerberosAuthentication, sKerberosOrLocalPasswd, sKerberosTicketCleanup,
-	sKerberosGetAFSToken, sPasswordAuthentication,
+	sKerberosGetAFSToken, sKerberosUniqueCCache, sPasswordAuthentication,
 	sKbdInteractiveAuthentication, sListenAddress, sAddressFamily,
 	sPrintMotd, sPrintLastLog, sIgnoreRhosts,
 	sX11Forwarding, sX11DisplayOffset, sX11UseLocalhost,
@@ -589,11 +592,13 @@ static struct {
 #else
 	{ "kerberosgetafstoken", sUnsupported, SSHCFG_GLOBAL },
 #endif
+	{ "kerberosuniqueccache", sKerberosUniqueCCache, SSHCFG_GLOBAL },
 #else
 	{ "kerberosauthentication", sUnsupported, SSHCFG_ALL },
 	{ "kerberosorlocalpasswd", sUnsupported, SSHCFG_GLOBAL },
 	{ "kerberosticketcleanup", sUnsupported, SSHCFG_GLOBAL },
 	{ "kerberosgetafstoken", sUnsupported, SSHCFG_GLOBAL },
+	{ "kerberosuniqueccache", sUnsupported, SSHCFG_GLOBAL },
 #endif
 	{ "kerberostgtpassing", sUnsupported, SSHCFG_GLOBAL },
 	{ "afstokenpassing", sUnsupported, SSHCFG_GLOBAL },
@@ -1645,6 +1650,10 @@ process_server_config_line_depth(ServerOptions *options, char *line,
 		intptr = &options->kerberos_get_afs_token;
 		goto parse_flag;
 
+	case sKerberosUniqueCCache:
+		intptr = &options->kerberos_unique_ccache;
+		goto parse_flag;
+
 	case sGssAuthentication:
 		intptr = &options->gss_authentication;
 		goto parse_flag;
@@ -3027,6 +3036,7 @@ dump_config(ServerOptions *o)
 # ifdef USE_AFS
 	dump_cfg_fmtint(sKerberosGetAFSToken, o->kerberos_get_afs_token);
 # endif
+	dump_cfg_fmtint(sKerberosUniqueCCache, o->kerberos_unique_ccache);
 #endif
 #ifdef GSSAPI
 	dump_cfg_fmtint(sGssAuthentication, o->gss_authentication);
diff --git a/servconf.h b/servconf.h
index 7ad43de..8f2eec3 100644
--- a/servconf.h
+++ b/servconf.h
@@ -140,6 +140,8 @@ typedef struct {
 						 * file on logout. */
 	int     kerberos_get_afs_token;		/* If true, try to get AFS token if
 						 * authenticated with Kerberos. */
+	int     kerberos_unique_ccache;		/* If true, the acquired ticket will
+						 * be stored in per-session ccache */
 	int     gss_authentication;	/* If true, permit GSSAPI authentication */
 	int     gss_cleanup_creds;	/* If true, destroy cred cache on logout */
 	int     gss_strict_acceptor;	/* If true, restrict the GSSAPI acceptor name */
diff --git a/session.c b/session.c
index 89dcfda..7241b0a 100644
--- a/session.c
+++ b/session.c
@@ -1013,7 +1013,8 @@ do_setup_env(struct ssh *ssh, Session *s, const char *shell)
 	/* Allow any GSSAPI methods that we've used to alter
 	 * the child's environment as they see fit
 	 */
-	ssh_gssapi_do_child(&env, &envsize);
+	if (s->authctxt->krb5_set_env)
+		ssh_gssapi_do_child(&env, &envsize);
 #endif
 
 	/* Set basic environment. */
@@ -1089,7 +1090,7 @@ do_setup_env(struct ssh *ssh, Session *s, const char *shell)
 	}
 #endif
 #ifdef KRB5
-	if (s->authctxt->krb5_ccname)
+	if (s->authctxt->krb5_ccname && s->authctxt->krb5_set_env)
 		child_set_env(&env, &envsize, "KRB5CCNAME",
 		    s->authctxt->krb5_ccname);
 #endif
diff --git a/ssh-gss.h b/ssh-gss.h
index a8af117..1bd1d2b 100644
--- a/ssh-gss.h
+++ b/ssh-gss.h
@@ -83,7 +83,7 @@ typedef struct ssh_gssapi_mech_struct {
 	int (*dochild) (ssh_gssapi_client *);
 	int (*userok) (ssh_gssapi_client *, char *);
 	int (*localname) (ssh_gssapi_client *, char **);
-	void (*storecreds) (ssh_gssapi_client *);
+	int (*storecreds) (ssh_gssapi_client *);
 } ssh_gssapi_mech;
 
 typedef struct {
@@ -131,7 +131,7 @@ int ssh_gssapi_userok(char *name);
 OM_uint32 ssh_gssapi_checkmic(Gssctxt *, gss_buffer_t, gss_buffer_t);
 void ssh_gssapi_do_child(char ***, u_int *);
 void ssh_gssapi_cleanup_creds(void);
-void ssh_gssapi_storecreds(void);
+int ssh_gssapi_storecreds(void);
 const char *ssh_gssapi_displayname(void);
 
 #endif /* GSSAPI */
diff --git a/sshd.c b/sshd.c
index 264e81a..8706d61 100644
--- a/sshd.c
+++ b/sshd.c
@@ -2292,7 +2292,7 @@ main(int ac, char **av)
 #ifdef GSSAPI
 	if (options.gss_authentication) {
 		temporarily_use_uid(authctxt->pw);
-		ssh_gssapi_storecreds();
+		authctxt->krb5_set_env = ssh_gssapi_storecreds();
 		restore_uid();
 	}
 #endif
diff --git a/sshd_config.5 b/sshd_config.5
index 7e1a56c..1aaeaed 100644
--- a/sshd_config.5
+++ b/sshd_config.5
@@ -994,6 +994,14 @@ Specifies whether to automatically destroy the user's ticket cache
 file on logout.
 The default is
 .Cm yes .
+.It Cm KerberosUniqueCCache
+Specifies whether to store the acquired tickets in the per-session credential
+cache under /tmp/ or whether to use per-user credential cache as configured in
+.Pa /etc/krb5.conf .
+The default value
+.Cm no
+can lead to overwriting previous tickets by subseqent connections to the same
+user account.
 .It Cm KexAlgorithms
 Specifies the available KEX (Key Exchange) algorithms.
 Multiple algorithms must be comma-separated.
-- 
2.41.0