Support AD style kerberos automatically in rpc.gss

An Active Directory KDC will only grant a TGT for UPNs, getting a TGT for SPNs is not possible:

$ kinit -k host/[email protected]
kinit: Client not found in Kerberos database while getting initial credentials

The correct thing to do for machine credentials is to get a TGT for the computer UPN <HOSTNAME>$@REALM:

$ kinit -k IB5\$
$ klist
12/22/10 11:43:47  12/22/10 21:43:47  krbtgt/[email protected]

Samba automatically creates /etc/krb5.keytab entry for the computer UPN, this patch makes gssd_refresh_krb5_machine_credential prefer it above the SPNs if it is present.

The net result is that nfs client works automatically out of the box if samba has been used to setup kerberos via 'net ads join' 'net ads keytab create'

Tested using Windows Server 2003 R2 as the AD server.

Signed-off-by Jason Gunthorpe <[email protected]>

---
utils/gssd/gssd.man | 5 ++++
utils/gssd/krb5_util.c | 62 ++++++++++++++++++++++++++++++++++--------------

2 files changed, 49 insertions(+), 18 deletions(-)

I'm still looking into what to do for AD in the server case when process_krb5_upcall is called with service == nfs. Some references suggest setting AD's userPrincipalName to the nfs SPN, but it would be really nice if that wasn't necessary.

Shouldn't it be possible to use the a ticket provided from the client to send back an unsolicted reply??

Thanks,
Jason

utils/gssd/gssd.man +0 -0

index 0a23cd6..073379d 100644
@@ -53,6 +53,8 @@ To be more consistent with other implementations, we now look for

specific keytab entries. The search order for keytabs to be used for "machine credentials" is now:
.br
+ <HOSTNAME>$@<REALM>
+.br
root/<hostname>@<REALM>
.br
nfs/<hostname>@<REALM>

utils/gssd/gssd.man +0 -0

@@ -64,6 +66,9 @@ for "machine credentials" is now:
  nfs/<anyname>@<REALM>

.br
host/<anyname>@<REALM>
+.IP

utils/gssd/gssd.man +2 -0

+If this search order does not use the correct key then provide a
+keytab file that contains only correct keys.

.TP
.B -p path
Tells

utils/gssd/krb5_util.c +44 -18

index f071600..4b13fa1 100644
@@ -768,6 +768,7 @@ find_keytab_entry(krb5_context context, krb5_keytab kt, const char *hostname,
 	krb5_error_code code;
 	char **realmnames = NULL;
 	char myhostname[NI_MAXHOST], targethostname[NI_MAXHOST];
+	char myhostad[NI_MAXHOST+1];
 	int i, j, retval;
 	char *default_realm = NULL;
 	char *realm;

@@ -789,6 +790,14 @@ find_keytab_entry(krb5_context context, krb5_keytab kt, const char *hostname,
 		printerr(1, "%s while getting local hostname\n", k5err);
 		goto out;
 	}
+
+	/* Compute the active directory machine name HOST$ */
+	strcpy(myhostad, myhostname);
+	for (i = 0; myhostad[i] != 0; ++i)
+		myhostad[i] = toupper(myhostad[i]);
+	myhostad[i] = '$';
+	myhostad[i+1] = 0;
+
 	retval = get_full_hostname(myhostname, myhostname, sizeof(myhostname));
 	if (retval)
 		goto out;

@@ -833,32 +842,47 @@ find_keytab_entry(krb5_context context, krb5_keytab kt, const char *hostname,
 		if (strcmp(realm, default_realm) == 0)
 			tried_default = 1;
 		for (j = 0; svcnames[j] != NULL; j++) {
-			code = krb5_build_principal_ext(context, &princ,
-							strlen(realm),
-							realm,
-							strlen(svcnames[j]),
-							svcnames[j],
-							strlen(myhostname),
-							myhostname,
-							NULL);
+			char spn[300];
+
+			/*
+			 * The special svcname "$" means 'try the active
+			 * directory machine account'
+			 */
+			if (strcmp(svcnames[j],"$") == 0) {
+				snprintf(spn, sizeof(spn), "%s@%s", myhostad, realm);
+				code = krb5_build_principal_ext(context, &princ,
+								strlen(realm),
+								realm,
+								strlen(myhostad),
+								myhostad,
+								NULL);
+			} else {
+				snprintf(spn, sizeof(spn), "%s/%s@%s",
+					 svcnames[j], myhostname, realm);
+				code = krb5_build_principal_ext(context, &princ,
+								strlen(realm),
+								realm,
+								strlen(svcnames[j]),
+								svcnames[j],
+								strlen(myhostname),
+								myhostname,
+								NULL);
+			}
+
 			if (code) {
 				k5err = gssd_k5_err_msg(context, code);
-				printerr(1, "%s while building principal for "
-					 "'%s/%s@%s'\n", k5err, svcnames[j],
-					 myhostname, realm);
+				printerr(1, "%s while building principal for '%s'\n",
+					 k5err, spn);
 				continue;
 			}
 			code = krb5_kt_get_entry(context, kt, princ, 0, 0, kte);
 			krb5_free_principal(context, princ);
 			if (code) {
 				k5err = gssd_k5_err_msg(context, code);
-				printerr(3, "%s while getting keytab entry for "
-					 "'%s/%s@%s'\n", k5err, svcnames[j],
-					 myhostname, realm);
+				printerr(3, "%s while getting keytab entry for '%s'\n",
+					 k5err, spn);
 			} else {
-				printerr(3, "Success getting keytab entry for "
-					 "'%s/%s@%s'\n",
-					 svcnames[j], myhostname, realm);
+				printerr(3, "Success getting keytab entry for '%s'\n",spn);
 				retval = 0;
 				goto out;
 			}

@@ -870,6 +894,8 @@ find_keytab_entry(krb5_context context, krb5_keytab kt, const char *hostname,
 		 */
 		for (j = 0; svcnames[j] != NULL; j++) {
 			int found = 0;
+			if (strcmp(svcnames[j],"$") == 0)
+				continue;
 			code = gssd_search_krb5_keytab(context, kt, realm,
 						       svcnames[j], &found, kte);
 			if (!code && found) {

@@ -1160,7 +1186,7 @@ gssd_refresh_krb5_machine_credential(char *hostname,
 	krb5_keytab kt = NULL;;
 	int retval = 0;
 	char *k5err = NULL;
-	const char *svcnames[4] = { "root", "nfs", "host", NULL };
+	const char *svcnames[5] = { "$", "root", "nfs", "host", NULL };
 
 	/*
 	 * If a specific service name was specified, use it.

Signature · 7 lines

1.7.1


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Quoted 20 lines · Jason Gunthorpe

An Active Directory KDC will only grant a TGT for UPNs, getting a TGT for SPNs is not possible:

$ kinit -k host/[email protected]
kinit: Client not found in Kerberos database while getting initial credentials

The correct thing to do for machine credentials is to get a TGT for the computer UPN <HOSTNAME>$@REALM:

$ kinit -k IB5\$
$ klist
12/22/10 11:43:47  12/22/10 21:43:47  krbtgt/[email protected]

Samba automatically creates /etc/krb5.keytab entry for the computer UPN, this patch makes gssd_refresh_krb5_machine_credential prefer it above the SPNs if it is present.

The net result is that nfs client works automatically out of the box if samba has been used to setup kerberos via 'net ads join' 'net ads keytab create'

Quoted 1 line

Tested using Windows Server 2003 R2 as the AD server.

This is basically what I did earlier, see:

http://marc.info/?l=linux-nfs&m=128108638228797&w=2

though I still haven't cleaned it up as promised..

Quoted 147 lines

Signed-off-by Jason Gunthorpe <[email protected]>

utils/gssd/gssd.man | 5 ++++
utils/gssd/krb5_util.c | 62 ++++++++++++++++++++++++++++++++++--------------

2 files changed, 49 insertions(+), 18 deletions(-)

I'm still looking into what to do for AD in the server case when process_krb5_upcall is called with service == nfs. Some references suggest setting AD's userPrincipalName to the nfs SPN, but it would be really nice if that wasn't necessary.

Shouldn't it be possible to use the a ticket provided from the client to send back an unsolicted reply??

Thanks,
Jason

utils/gssd/gssd.man +1 -0

index 0a23cd6..073379d 100644
+++ b/utils/gssd/gssd.man

@@ -53,6 +53,8 @@ To be more consistent with other implementations, we now look for

specific keytab entries. The search order for keytabs to be used for "machine credentials" is now:
.br
+ <HOSTNAME>$@<REALM>
+.br
root/<hostname>@<REALM>
.br
nfs/<hostname>@<REALM>

utils/gssd/gssd.man +0 -0

@@ -64,6 +66,9 @@ for "machine credentials" is now:
 nfs/<anyname>@<REALM>

.br
host/<anyname>@<REALM>
+.IP

utils/gssd/gssd.man +2 -0

+If this search order does not use the correct key then provide a
+keytab file that contains only correct keys.

.TP
.B -p path
Tells

utils/gssd/krb5_util.c +45 -18

index f071600..4b13fa1 100644
+++ b/utils/gssd/krb5_util.c

@@ -768,6 +768,7 @@ find_keytab_entry(krb5_context context, krb5_keytab kt, const char *hostname,
 	krb5_error_code code;
 	char **realmnames = NULL;
 	char myhostname[NI_MAXHOST], targethostname[NI_MAXHOST];
+	char myhostad[NI_MAXHOST+1];
 	int i, j, retval;
 	char *default_realm = NULL;
 	char *realm;

@@ -789,6 +790,14 @@ find_keytab_entry(krb5_context context, krb5_keytab kt, const char *hostname,
 		printerr(1, "%s while getting local hostname\n", k5err);
 		goto out;
 	}
+
+	/* Compute the active directory machine name HOST$ */
+	strcpy(myhostad, myhostname);
+	for (i = 0; myhostad[i] != 0; ++i)
+		myhostad[i] = toupper(myhostad[i]);
+	myhostad[i] = '$';
+	myhostad[i+1] = 0;
+
 	retval = get_full_hostname(myhostname, myhostname, sizeof(myhostname));
 	if (retval)
 		goto out;

@@ -833,32 +842,47 @@ find_keytab_entry(krb5_context context, krb5_keytab kt, const char *hostname,
 		if (strcmp(realm, default_realm) == 0)
 			tried_default = 1;
 		for (j = 0; svcnames[j] != NULL; j++) {
-			code = krb5_build_principal_ext(context, &princ,
-							strlen(realm),
-							realm,
-							strlen(svcnames[j]),
-							svcnames[j],
-							strlen(myhostname),
-							myhostname,
-							NULL);
+			char spn[300];
+
+			/*
+			 * The special svcname "$" means 'try the active
+			 * directory machine account'
+			 */
+			if (strcmp(svcnames[j],"$") == 0) {
+				snprintf(spn, sizeof(spn), "%s@%s", myhostad, realm);
+				code = krb5_build_principal_ext(context, &princ,
+								strlen(realm),
+								realm,
+								strlen(myhostad),
+								myhostad,
+								NULL);
+			} else {
+				snprintf(spn, sizeof(spn), "%s/%s@%s",
+					 svcnames[j], myhostname, realm);
+				code = krb5_build_principal_ext(context, &princ,
+								strlen(realm),
+								realm,
+								strlen(svcnames[j]),
+								svcnames[j],
+								strlen(myhostname),
+								myhostname,
+								NULL);
+			}
+
 			if (code) {
 				k5err = gssd_k5_err_msg(context, code);
-				printerr(1, "%s while building principal for "
-					 "'%s/%s@%s'\n", k5err, svcnames[j],
-					 myhostname, realm);
+				printerr(1, "%s while building principal for '%s'\n",
+					 k5err, spn);
 				continue;
 			}
 			code = krb5_kt_get_entry(context, kt, princ, 0, 0, kte);
 			krb5_free_principal(context, princ);
 			if (code) {
 				k5err = gssd_k5_err_msg(context, code);
-				printerr(3, "%s while getting keytab entry for "
-					 "'%s/%s@%s'\n", k5err, svcnames[j],
-					 myhostname, realm);
+				printerr(3, "%s while getting keytab entry for '%s'\n",
+					 k5err, spn);
 			} else {
-				printerr(3, "Success getting keytab entry for "
-					 "'%s/%s@%s'\n",
-					 svcnames[j], myhostname, realm);
+				printerr(3, "Success getting keytab entry for '%s'\n",spn);
 				retval = 0;
 				goto out;
 			}

@@ -870,6 +894,8 @@ find_keytab_entry(krb5_context context, krb5_keytab kt, const char *hostname,
 		 */
 		for (j = 0; svcnames[j] != NULL; j++) {
 			int found = 0;
+			if (strcmp(svcnames[j],"$") == 0)
+				continue;
 			code = gssd_search_krb5_keytab(context, kt, realm,
 						       svcnames[j], &found, kte);
 			if (!code && found) {

@@ -1160,7 +1186,7 @@ gssd_refresh_krb5_machine_credential(char *hostname,
 	krb5_keytab kt = NULL;;
 	int retval = 0;
 	char *k5err = NULL;
-	const char *svcnames[4] = { "root", "nfs", "host", NULL };
+	const char *svcnames[5] = { "$", "root", "nfs", "host", NULL };
 
 	/*
 	 * If a specific service name was specified, use it.

Quoted 26 lines · Timo Aaltonen

Quoted 16 lines · Jason Gunthorpe

An Active Directory KDC will only grant a TGT for UPNs, getting a TGT for SPNs is not possible:

$ kinit -k host/[email protected]
kinit: Client not found in Kerberos database while getting initial credentials

The correct thing to do for machine credentials is to get a TGT for the computer UPN <HOSTNAME>$@REALM:

$ kinit -k IB5\$
$ klist
12/22/10 11:43:47  12/22/10 21:43:47  krbtgt/[email protected]

Samba automatically creates /etc/krb5.keytab entry for the computer UPN, this patch makes gssd_refresh_krb5_machine_credential prefer it above the SPNs if it is present.

Quoted 5 lines

The net result is that nfs client works automatically out of the box if samba has been used to setup kerberos via 'net ads join' 'net ads keytab create'

Tested using Windows Server 2003 R2 as the AD server.

This is basically what I did earlier, see:

Quoted 3 lines

http://marc.info/?l=linux-nfs&m=128108638228797&w=2

though I still haven't cleaned it up as promised..

Right, mine is a bit more complete (man page updated, etc) but it does the same thing.

Maybe we can get a nfs-utils maintainer to comment this time?

An Active Directory KDC will only grant a TGT for UPNs, getting a TGT for SPNs is not possible:

$ kinit -k host/[email protected]
kinit: Client not found in Kerberos database while getting initial credentials

The correct thing to do for machine credentials is to get a TGT for the computer UPN <HOSTNAME>$@REALM:

$ kinit -k IB5\$
$ klist
12/22/10 11:43:47  12/22/10 21:43:47  krbtgt/[email protected]

Samba automatically creates /etc/krb5.keytab entry for the computer UPN, this patch makes gssd_refresh_krb5_machine_credential prefer it above the SPNs if it is present.

The net result is that nfs client works automatically out of the box if samba has been used to setup kerberos via 'net ads join' 'net ads keytab create'

Tested using Windows Server 2003 R2 as the AD server.

Signed-off-by Jason Gunthorpe <[email protected]>

---
 utils/gssd/gssd.man    |    5 ++++
 utils/gssd/krb5_util.c |   62 ++++++++++++++++++++++++++++++++++--------------
 2 files changed, 49 insertions(+), 18 deletions(-)

I'm still looking into what to do for AD in the server case when process_krb5_upcall is called with service == nfs. Some references suggest setting AD's userPrincipalName to the nfs SPN, but it would be really nice if that wasn't necessary.

Shouldn't it be possible to use the a ticket provided from the client to send back an unsolicted reply??

Thanks,
Jason

utils/gssd/gssd.man +5 -0

index 0a23cd6..073379d 100644
@@ -53,6 +53,8 @@ To be more consistent with other implementations, we now look for
 specific keytab entries.  The search order for keytabs to be used
 for "machine credentials" is now:
 .br
+  <HOSTNAME>$@<REALM>
+.br
   root/<hostname>@<REALM>
 .br
   nfs/<hostname>@<REALM>

@@ -64,6 +66,9 @@ for "machine credentials" is now:
   nfs/<anyname>@<REALM>
 .br
   host/<anyname>@<REALM>
+.IP
+If this search order does not use the correct key then provide a
+keytab file that contains only correct keys.
 .TP
 .B -p path
 Tells

utils/gssd/krb5_util.c +44 -18

index f071600..4b13fa1 100644
@@ -768,6 +768,7 @@ find_keytab_entry(krb5_context context, krb5_keytab kt, const char *hostname,
 	krb5_error_code code;
 	char **realmnames = NULL;
 	char myhostname[NI_MAXHOST], targethostname[NI_MAXHOST];
+	char myhostad[NI_MAXHOST+1];
 	int i, j, retval;
 	char *default_realm = NULL;
 	char *realm;

@@ -789,6 +790,14 @@ find_keytab_entry(krb5_context context, krb5_keytab kt, const char *hostname,
 		printerr(1, "%s while getting local hostname\n", k5err);
 		goto out;
 	}
+
+	/* Compute the active directory machine name HOST$ */
+	strcpy(myhostad, myhostname);
+	for (i = 0; myhostad[i] != 0; ++i)
+		myhostad[i] = toupper(myhostad[i]);
+	myhostad[i] = '$';
+	myhostad[i+1] = 0;
+
 	retval = get_full_hostname(myhostname, myhostname, sizeof(myhostname));
 	if (retval)
 		goto out;

@@ -833,32 +842,47 @@ find_keytab_entry(krb5_context context, krb5_keytab kt, const char *hostname,
 		if (strcmp(realm, default_realm) == 0)
 			tried_default = 1;
 		for (j = 0; svcnames[j] != NULL; j++) {
-			code = krb5_build_principal_ext(context, &princ,
-							strlen(realm),
-							realm,
-							strlen(svcnames[j]),
-							svcnames[j],
-							strlen(myhostname),
-							myhostname,
-							NULL);
+			char spn[300];
+
+			/*
+			 * The special svcname "$" means 'try the active
+			 * directory machine account'
+			 */
+			if (strcmp(svcnames[j],"$") == 0) {
+				snprintf(spn, sizeof(spn), "%s@%s", myhostad, realm);
+				code = krb5_build_principal_ext(context, &princ,
+								strlen(realm),
+								realm,
+								strlen(myhostad),
+								myhostad,
+								NULL);
+			} else {
+				snprintf(spn, sizeof(spn), "%s/%s@%s",
+					 svcnames[j], myhostname, realm);
+				code = krb5_build_principal_ext(context, &princ,
+								strlen(realm),
+								realm,
+								strlen(svcnames[j]),
+								svcnames[j],
+								strlen(myhostname),
+								myhostname,
+								NULL);
+			}
+
 			if (code) {
 				k5err = gssd_k5_err_msg(context, code);
-				printerr(1, "%s while building principal for "
-					 "'%s/%s@%s'\n", k5err, svcnames[j],
-					 myhostname, realm);
+				printerr(1, "%s while building principal for '%s'\n",
+					 k5err, spn);
 				continue;
 			}
 			code = krb5_kt_get_entry(context, kt, princ, 0, 0, kte);
 			krb5_free_principal(context, princ);
 			if (code) {
 				k5err = gssd_k5_err_msg(context, code);
-				printerr(3, "%s while getting keytab entry for "
-					 "'%s/%s@%s'\n", k5err, svcnames[j],
-					 myhostname, realm);
+				printerr(3, "%s while getting keytab entry for '%s'\n",
+					 k5err, spn);
 			} else {
-				printerr(3, "Success getting keytab entry for "
-					 "'%s/%s@%s'\n",
-					 svcnames[j], myhostname, realm);
+				printerr(3, "Success getting keytab entry for '%s'\n",spn);
 				retval = 0;
 				goto out;
 			}

@@ -870,6 +894,8 @@ find_keytab_entry(krb5_context context, krb5_keytab kt, const char *hostname,
 		 */
 		for (j = 0; svcnames[j] != NULL; j++) {
 			int found = 0;
+			if (strcmp(svcnames[j],"$") == 0)
+				continue;
 			code = gssd_search_krb5_keytab(context, kt, realm,
 						       svcnames[j], &found, kte);
 			if (!code && found) {

@@ -1160,7 +1186,7 @@ gssd_refresh_krb5_machine_credential(char *hostname,
 	krb5_keytab kt = NULL;;
 	int retval = 0;
 	char *k5err = NULL;
-	const char *svcnames[4] = { "root", "nfs", "host", NULL };
+	const char *svcnames[5] = { "$", "root", "nfs", "host", NULL };
 
 	/*
 	 * If a specific service name was specified, use it.