krb5 commit: Add support to query the SSF of a GSS context

https://github.com/krb5/krb5/commit/7feb7da54c0321b5a3eeb6c3797846a3cf7eda28
commit 7feb7da54c0321b5a3eeb6c3797846a3cf7eda28
Author: Simo Sorce <[email protected]>
Date:   Thu Mar 30 11:27:09 2017 -0400

    Add support to query the SSF of a GSS context
    
    Cyrus SASL provides a Security Strength Factor number to assess the
    relative "strength" of the negotiated mechanism, and applications
    sometimes make access control decisions based on it.
    
    Add a call that allows us to query the mechanism that established the
    GSS security context to ask what is the current SSF, based on the
    enctype of the session key.
    
    ticket: 8569 (new)

 src/include/k5-int.h                    |    1 +
 src/lib/crypto/krb/crypto_int.h         |    1 +
 src/lib/crypto/krb/enctype_util.c       |   16 +++++++++++++++
 src/lib/crypto/krb/etypes.c             |   33 ++++++++++++++++--------------
 src/lib/crypto/libk5crypto.exports      |    1 +
 src/lib/gssapi/generic/gssapi_ext.h     |   11 ++++++++++
 src/lib/gssapi/generic/gssapi_generic.c |    9 ++++++++
 src/lib/gssapi/krb5/gssapiP_krb5.h      |    6 +++++
 src/lib/gssapi/krb5/gssapi_krb5.c       |    4 +++
 src/lib/gssapi/krb5/inq_context.c       |   27 +++++++++++++++++++++++++
 src/lib/gssapi/libgssapi_krb5.exports   |    1 +
 src/lib/gssapi32.def                    |    1 +
 src/lib/krb5_32.def                     |    3 ++
 src/tests/gssapi/t_enctypes.c           |   14 +++++++++++++
 14 files changed, 113 insertions(+), 15 deletions(-)

diff --git a/src/include/k5-int.h b/src/include/k5-int.h
index ddeebc4..78ebaf3 100644
--- a/src/include/k5-int.h
+++ b/src/include/k5-int.h
@@ -2113,6 +2113,7 @@ krb5_get_tgs_ktypes(krb5_context, krb5_const_principal, krb5_enctype **);
 krb5_boolean krb5_is_permitted_enctype(krb5_context, krb5_enctype);
 
 krb5_boolean KRB5_CALLCONV krb5int_c_weak_enctype(krb5_enctype);
+krb5_error_code k5_enctype_to_ssf(krb5_enctype enctype, unsigned int *ssf_out);
 
 krb5_error_code krb5_kdc_rep_decrypt_proc(krb5_context, const krb5_keyblock *,
                                           krb5_const_pointer, krb5_kdc_rep *);
diff --git a/src/lib/crypto/krb/crypto_int.h b/src/lib/crypto/krb/crypto_int.h
index d75b49c..e509929 100644
--- a/src/lib/crypto/krb/crypto_int.h
+++ b/src/lib/crypto/krb/crypto_int.h
@@ -111,6 +111,7 @@ struct krb5_keytypes {
     prf_func prf;
     krb5_cksumtype required_ctype;
     krb5_flags flags;
+    unsigned int ssf;
 };
 
 #define ETYPE_WEAK 1
diff --git a/src/lib/crypto/krb/enctype_util.c b/src/lib/crypto/krb/enctype_util.c
index 0ed74bd..b1b40e7 100644
--- a/src/lib/crypto/krb/enctype_util.c
+++ b/src/lib/crypto/krb/enctype_util.c
@@ -131,3 +131,19 @@ krb5_enctype_to_name(krb5_enctype enctype, krb5_boolean shortest,
         return ENOMEM;
     return 0;
 }
+
+/* The security of a mechanism cannot be summarized with a simple integer
+ * value, but we provide a per-enctype value for Cyrus SASL's SSF. */
+krb5_error_code
+k5_enctype_to_ssf(krb5_enctype enctype, unsigned int *ssf_out)
+{
+    const struct krb5_keytypes *ktp;
+
+    *ssf_out = 0;
+
+    ktp = find_enctype(enctype);
+    if (ktp == NULL)
+        return EINVAL;
+    *ssf_out = ktp->ssf;
+    return 0;
+}
diff --git a/src/lib/crypto/krb/etypes.c b/src/lib/crypto/krb/etypes.c
index 0e5e977..53d4a5c 100644
--- a/src/lib/crypto/krb/etypes.c
+++ b/src/lib/crypto/krb/etypes.c
@@ -42,7 +42,7 @@ const struct krb5_keytypes krb5int_enctypes_list[] = {
       krb5int_des_string_to_key, k5_rand2key_des,
       krb5int_des_prf,
       CKSUMTYPE_RSA_MD5_DES,
-      ETYPE_WEAK },
+      ETYPE_WEAK, 56 },
     { ENCTYPE_DES_CBC_MD4,
       "des-cbc-md4", { 0 }, "DES cbc mode with RSA-MD4",
       &krb5int_enc_des, &krb5int_hash_md4,
@@ -51,7 +51,7 @@ const struct krb5_keytypes krb5int_enctypes_list[] = {
       krb5int_des_string_to_key, k5_rand2key_des,
       krb5int_des_prf,
       CKSUMTYPE_RSA_MD4_DES,
-      ETYPE_WEAK },
+      ETYPE_WEAK, 56 },
     { ENCTYPE_DES_CBC_MD5,
       "des-cbc-md5", { "des" }, "DES cbc mode with RSA-MD5",
       &krb5int_enc_des, &krb5int_hash_md5,
@@ -60,7 +60,7 @@ const struct krb5_keytypes krb5int_enctypes_list[] = {
       krb5int_des_string_to_key, k5_rand2key_des,
       krb5int_des_prf,
       CKSUMTYPE_RSA_MD5_DES,
-      ETYPE_WEAK },
+      ETYPE_WEAK, 56 },
     { ENCTYPE_DES_CBC_RAW,
       "des-cbc-raw", { 0 }, "DES cbc mode raw",
       &krb5int_enc_des, NULL,
@@ -69,7 +69,7 @@ const struct krb5_keytypes krb5int_enctypes_list[] = {
       krb5int_des_string_to_key, k5_rand2key_des,
       krb5int_des_prf,
       0,
-      ETYPE_WEAK },
+      ETYPE_WEAK, 56 },
     { ENCTYPE_DES3_CBC_RAW,
       "des3-cbc-raw", { 0 }, "Triple DES cbc mode raw",
       &krb5int_enc_des3, NULL,
@@ -78,7 +78,7 @@ const struct krb5_keytypes krb5int_enctypes_list[] = {
       krb5int_dk_string_to_key, k5_rand2key_des3,
       NULL, /*PRF*/
       0,
-      ETYPE_WEAK },
+      ETYPE_WEAK, 112 },
 
     { ENCTYPE_DES3_CBC_SHA1,
       "des3-cbc-sha1", { "des3-hmac-sha1", "des3-cbc-sha1-kd" },
@@ -89,7 +89,7 @@ const struct krb5_keytypes krb5int_enctypes_list[] = {
       krb5int_dk_string_to_key, k5_rand2key_des3,
       krb5int_dk_prf,
       CKSUMTYPE_HMAC_SHA1_DES3,
-      0 /*flags*/ },
+      0 /*flags*/, 112 },
 
     { ENCTYPE_DES_HMAC_SHA1,
       "des-hmac-sha1", { 0 }, "DES with HMAC/sha1",
@@ -99,7 +99,10 @@ const struct krb5_keytypes krb5int_enctypes_list[] = {
       krb5int_dk_string_to_key, k5_rand2key_des,
       NULL, /*PRF*/
       0,
-      ETYPE_WEAK },
+      ETYPE_WEAK, 56 },
+
+    /* rc4-hmac uses a 128-bit key, but due to weaknesses in the RC4 cipher, we
+     * consider its strength degraded and assign it an SSF value of 64. */
     { ENCTYPE_ARCFOUR_HMAC,
       "arcfour-hmac", { "rc4-hmac", "arcfour-hmac-md5" },
       "ArcFour with HMAC/md5",
@@ -110,7 +113,7 @@ const struct krb5_keytypes krb5int_enctypes_list[] = {
       krb5int_arcfour_decrypt, krb5int_arcfour_string_to_key,
       k5_rand2key_direct, krb5int_arcfour_prf,
       CKSUMTYPE_HMAC_MD5_ARCFOUR,
-      0 /*flags*/ },
+      0 /*flags*/, 64 },
     { ENCTYPE_ARCFOUR_HMAC_EXP,
       "arcfour-hmac-exp", { "rc4-hmac-exp", "arcfour-hmac-md5-exp" },
       "Exportable ArcFour with HMAC/md5",
@@ -121,7 +124,7 @@ const struct krb5_keytypes krb5int_enctypes_list[] = {
       krb5int_arcfour_decrypt, krb5int_arcfour_string_to_key,
       k5_rand2key_direct, krb5int_arcfour_prf,
       CKSUMTYPE_HMAC_MD5_ARCFOUR,
-      ETYPE_WEAK
+      ETYPE_WEAK, 40
     },
 
     { ENCTYPE_AES128_CTS_HMAC_SHA1_96,
@@ -133,7 +136,7 @@ const struct krb5_keytypes krb5int_enctypes_list[] = {
       krb5int_aes_string_to_key, k5_rand2key_direct,
       krb5int_dk_prf,
       CKSUMTYPE_HMAC_SHA1_96_AES128,
-      0 /*flags*/ },
+      0 /*flags*/, 128 },
     { ENCTYPE_AES256_CTS_HMAC_SHA1_96,
       "aes256-cts-hmac-sha1-96", { "aes256-cts", "aes256-sha1" },
       "AES-256 CTS mode with 96-bit SHA-1 HMAC",
@@ -143,7 +146,7 @@ const struct krb5_keytypes krb5int_enctypes_list[] = {
       krb5int_aes_string_to_key, k5_rand2key_direct,
       krb5int_dk_prf,
       CKSUMTYPE_HMAC_SHA1_96_AES256,
-      0 /*flags*/ },
+      0 /*flags*/, 256 },
 
     { ENCTYPE_CAMELLIA128_CTS_CMAC,
       "camellia128-cts-cmac", { "camellia128-cts" },
@@ -155,7 +158,7 @@ const struct krb5_keytypes krb5int_enctypes_list[] = {
       krb5int_camellia_string_to_key, k5_rand2key_direct,
       krb5int_dk_cmac_prf,
       CKSUMTYPE_CMAC_CAMELLIA128,
-      0 /*flags*/ },
+      0 /*flags*/, 128 },
     { ENCTYPE_CAMELLIA256_CTS_CMAC,
       "camellia256-cts-cmac", { "camellia256-cts" },
       "Camellia-256 CTS mode with CMAC",
@@ -166,7 +169,7 @@ const struct krb5_keytypes krb5int_enctypes_list[] = {
       krb5int_camellia_string_to_key, k5_rand2key_direct,
       krb5int_dk_cmac_prf,
       CKSUMTYPE_CMAC_CAMELLIA256,
-      0 /*flags */ },
+      0 /*flags */, 256 },
 
     { ENCTYPE_AES128_CTS_HMAC_SHA256_128,
       "aes128-cts-hmac-sha256-128", { "aes128-sha2" },
@@ -177,7 +180,7 @@ const struct krb5_keytypes krb5int_enctypes_list[] = {
       krb5int_aes2_string_to_key, k5_rand2key_direct,
       krb5int_aes2_prf,
       CKSUMTYPE_HMAC_SHA256_128_AES128,
-      0 /*flags*/ },
+      0 /*flags*/, 128 },
     { ENCTYPE_AES256_CTS_HMAC_SHA384_192,
       "aes256-cts-hmac-sha384-192", { "aes256-sha2" },
       "AES-256 CTS mode with 192-bit SHA-384 HMAC",
@@ -187,7 +190,7 @@ const struct krb5_keytypes krb5int_enctypes_list[] = {
       krb5int_aes2_string_to_key, k5_rand2key_direct,
       krb5int_aes2_prf,
       CKSUMTYPE_HMAC_SHA384_192_AES256,
-      0 /*flags*/ },
+      0 /*flags*/, 256 },
 };
 
 const int krb5int_enctypes_length =
diff --git a/src/lib/crypto/libk5crypto.exports b/src/lib/crypto/libk5crypto.exports
index 447e456..82eb5f3 100644
--- a/src/lib/crypto/libk5crypto.exports
+++ b/src/lib/crypto/libk5crypto.exports
@@ -108,3 +108,4 @@ krb5int_nfold
 k5_allow_weak_pbkdf2iter
 krb5_c_prfplus
 krb5_c_derive_prfplus
+k5_enctype_to_ssf
diff --git a/src/lib/gssapi/generic/gssapi_ext.h b/src/lib/gssapi/generic/gssapi_ext.h
index 9ad4421..9d3a7e7 100644
--- a/src/lib/gssapi/generic/gssapi_ext.h
+++ b/src/lib/gssapi/generic/gssapi_ext.h
@@ -575,4 +575,15 @@ gss_import_cred(
 }
 #endif
 
+/*
+ * When used with gss_inquire_sec_context_by_oid(), return a buffer set with
+ * the first member containing an unsigned 32-bit integer in network byte
+ * order.  This is the Security Strength Factor (SSF) associated with the
+ * secure channel established by the security context.  NOTE: This value is
+ * made available solely as an indication for use by APIs like Cyrus SASL that
+ * classify the strength of a secure channel via this number.  The strength of
+ * a channel cannot necessarily be represented by a simple number.
+ */
+GSS_DLLIMP extern gss_OID GSS_C_SEC_CONTEXT_SASL_SSF;
+
 #endif /* GSSAPI_EXT_H_ */
diff --git a/src/lib/gssapi/generic/gssapi_generic.c b/src/lib/gssapi/generic/gssapi_generic.c
index 5496aa3..fa144c2 100644
--- a/src/lib/gssapi/generic/gssapi_generic.c
+++ b/src/lib/gssapi/generic/gssapi_generic.c
@@ -157,6 +157,13 @@ static const gss_OID_desc const_oids[] = {
     {7, (void *)"\x2b\x06\x01\x05\x05\x0d\x19"},
     {7, (void *)"\x2b\x06\x01\x05\x05\x0d\x1a"},
     {7, (void *)"\x2b\x06\x01\x05\x05\x0d\x1b"},
+
+    /*
+     * GSS_SEC_CONTEXT_SASL_SSF_OID 1.2.840.113554.1.2.2.5.15
+     * iso(1) member-body(2) United States(840) mit(113554)
+     * infosys(1) gssapi(2) krb5(2) krb5-gssapi-ext(5) sasl-ssf(15)
+     */
+    {11, (void *)"\x2a\x86\x48\x86\xf7\x12\x01\x02\x02\x05\x0f"},
 };
 
 /* Here are the constants which point to the static structure above.
@@ -218,6 +225,8 @@ GSS_DLLIMP gss_const_OID GSS_C_MA_PFS               = oids+33;
 GSS_DLLIMP gss_const_OID GSS_C_MA_COMPRESS          = oids+34;
 GSS_DLLIMP gss_const_OID GSS_C_MA_CTX_TRANS         = oids+35;
 
+GSS_DLLIMP gss_OID GSS_C_SEC_CONTEXT_SASL_SSF = oids+36;
+
 static gss_OID_set_desc gss_ma_known_attrs_desc = { 27, oids+9 };
 gss_OID_set gss_ma_known_attrs = &gss_ma_known_attrs_desc;
 
diff --git a/src/lib/gssapi/krb5/gssapiP_krb5.h b/src/lib/gssapi/krb5/gssapiP_krb5.h
index cd65966..e92be88 100644
--- a/src/lib/gssapi/krb5/gssapiP_krb5.h
+++ b/src/lib/gssapi/krb5/gssapiP_krb5.h
@@ -1144,6 +1144,12 @@ gss_krb5int_extract_authtime_from_sec_context(OM_uint32 *,
                                               const gss_OID,
                                               gss_buffer_set_t *);
 
+#define GET_SEC_CONTEXT_SASL_SSF_OID_LENGTH 11
+#define GET_SEC_CONTEXT_SASL_SSF_OID "\x2a\x86\x48\x86\xf7\x12\x01\x02\x02\x05\x0f"
+OM_uint32
+gss_krb5int_sec_context_sasl_ssf(OM_uint32 *, const gss_ctx_id_t,
+                                 const gss_OID, gss_buffer_set_t *);
+
 #define GSS_KRB5_IMPORT_CRED_OID_LENGTH 11
 #define GSS_KRB5_IMPORT_CRED_OID "\x2a\x86\x48\x86\xf7\x12\x01\x02\x02\x05\x0d"
 
diff --git a/src/lib/gssapi/krb5/gssapi_krb5.c b/src/lib/gssapi/krb5/gssapi_krb5.c
index e12b662..43930dd 100644
--- a/src/lib/gssapi/krb5/gssapi_krb5.c
+++ b/src/lib/gssapi/krb5/gssapi_krb5.c
@@ -357,6 +357,10 @@ static struct {
     {
         {GSS_KRB5_EXTRACT_AUTHTIME_FROM_SEC_CONTEXT_OID_LENGTH, GSS_KRB5_EXTRACT_AUTHTIME_FROM_SEC_CONTEXT_OID},
         gss_krb5int_extract_authtime_from_sec_context
+    },
+    {
+        {GET_SEC_CONTEXT_SASL_SSF_OID_LENGTH, GET_SEC_CONTEXT_SASL_SSF_OID},
+        gss_krb5int_sec_context_sasl_ssf
     }
 };
 
diff --git a/src/lib/gssapi/krb5/inq_context.c b/src/lib/gssapi/krb5/inq_context.c
index 9024b3c..d2e466e 100644
--- a/src/lib/gssapi/krb5/inq_context.c
+++ b/src/lib/gssapi/krb5/inq_context.c
@@ -310,3 +310,30 @@ gss_krb5int_extract_authtime_from_sec_context(OM_uint32 *minor_status,
 
     return generic_gss_add_buffer_set_member(minor_status, &rep, data_set);
 }
+
+OM_uint32
+gss_krb5int_sec_context_sasl_ssf(OM_uint32 *minor_status,
+                                 const gss_ctx_id_t context_handle,
+                                 const gss_OID desired_object,
+                                 gss_buffer_set_t *data_set)
+{
+    krb5_gss_ctx_id_rec *ctx;
+    krb5_key key;
+    krb5_error_code code;
+    gss_buffer_desc ssfbuf;
+    unsigned int ssf;
+    uint8_t buf[4];
+
+    ctx = (krb5_gss_ctx_id_rec *)context_handle;
+    key = ctx->have_acceptor_subkey ? ctx->acceptor_subkey : ctx->subkey;
+
+    code = k5_enctype_to_ssf(key->keyblock.enctype, &ssf);
+    if (code)
+        return GSS_S_FAILURE;
+
+    store_32_be(ssf, buf);
+    ssfbuf.value = buf;
+    ssfbuf.length = sizeof(buf);
+
+    return generic_gss_add_buffer_set_member(minor_status, &ssfbuf, data_set);
+}
diff --git a/src/lib/gssapi/libgssapi_krb5.exports b/src/lib/gssapi/libgssapi_krb5.exports
index 16d38e9..b07f69f 100644
--- a/src/lib/gssapi/libgssapi_krb5.exports
+++ b/src/lib/gssapi/libgssapi_krb5.exports
@@ -38,6 +38,7 @@ GSS_C_MA_CBINDINGS
 GSS_C_MA_PFS
 GSS_C_MA_COMPRESS
 GSS_C_MA_CTX_TRANS
+GSS_C_SEC_CONTEXT_SASL_SSF
 gss_accept_sec_context
 gss_acquire_cred
 gss_acquire_cred_with_password
diff --git a/src/lib/gssapi32.def b/src/lib/gssapi32.def
index 4bf8c95..842f3d5 100644
--- a/src/lib/gssapi32.def
+++ b/src/lib/gssapi32.def
@@ -184,3 +184,4 @@ EXPORTS
 	GSS_KRB5_CRED_NO_CI_FLAGS_X			@147	DATA
 ; Added in 1.16
 	GSS_KRB5_GET_CRED_IMPERSONATOR			@148	DATA
+	GSS_C_SEC_CONTEXT_SASL_SSF			@149	DATA
diff --git a/src/lib/krb5_32.def b/src/lib/krb5_32.def
index e5b560d..f7b428e 100644
--- a/src/lib/krb5_32.def
+++ b/src/lib/krb5_32.def
@@ -470,3 +470,6 @@ EXPORTS
 	krb5_get_init_creds_opt_set_pac_request		@435
 	krb5int_trace					@436 ; PRIVATE GSSAPI
 	krb5_expand_hostname				@437
+
+; new in 1.16
+	k5_enctype_to_ssf				@438 ; PRIVATE GSSAPI
diff --git a/src/tests/gssapi/t_enctypes.c b/src/tests/gssapi/t_enctypes.c
index a2ad18f..3fd31e2 100644
--- a/src/tests/gssapi/t_enctypes.c
+++ b/src/tests/gssapi/t_enctypes.c
@@ -32,6 +32,7 @@
 
 #include "k5-int.h"
 #include "common.h"
+#include "gssapi_ext.h"
 
 /*
  * This test program establishes contexts with the krb5 mech, the default
@@ -86,6 +87,9 @@ main(int argc, char *argv[])
     gss_krb5_lucid_context_v1_t *ilucid, *alucid;
     gss_krb5_rfc1964_keydata_t *i1964, *a1964;
     gss_krb5_cfx_keydata_t *icfx, *acfx;
+    gss_buffer_set_t bufset = GSS_C_NO_BUFFER_SET;
+    gss_OID ssf_oid = GSS_C_SEC_CONTEXT_SASL_SSF;
+    unsigned int ssf;
     size_t count;
     void *lptr;
     int c;
@@ -139,6 +143,16 @@ main(int argc, char *argv[])
     establish_contexts(&mech_krb5, icred, acred, tname, flags, &ictx, &actx,
                        NULL, NULL, NULL);
 
+    /* Query the SSF value and range-check the result. */
+    major = gss_inquire_sec_context_by_oid(&minor, ictx, ssf_oid, &bufset);
+    check_gsserr("gss_inquire_sec_context_by_oid(ssf)", major, minor);
+    if (bufset->elements[0].length != 4)
+        errout("SSF buffer has unexpected length");
+    ssf = load_32_be(bufset->elements[0].value);
+    if (ssf < 56 || ssf > 256)
+        errout("SSF value not within acceptable range (56-256)");
+    (void)gss_release_buffer_set(&minor, &bufset);
+
     /* Export to lucid contexts. */
     major = gss_krb5_export_lucid_sec_context(&minor, &ictx, 1, &lptr);
     check_gsserr("gss_export_lucid_sec_context(initiator)", major, minor);