3 files changed, 59 insertions, 1 deletions

diff --git a/include/linux/sunrpc/gss_krb5_enctypes.h b/include/linux/sunrpc/gss_krb5_enctypes.h
index ec6234eee89c..981c89cef19d 100644
--- a/include/linux/sunrpc/gss_krb5_enctypes.h
+++ b/include/linux/sunrpc/gss_krb5_enctypes.h
@@ -1,4 +1,44 @@
+/* SPDX-License-Identifier: GPL-2.0 */
 /*
- * Dumb way to share this static piece of information with nfsd
+ * Define the string that exports the set of kernel-supported
+ * Kerberos enctypes. This list is sent via upcall to gssd, and
+ * is also exposed via the nfsd /proc API. The consumers generally
+ * treat this as an ordered list, where the first item in the list
+ * is the most preferred.
+ */
+
+#ifndef _LINUX_SUNRPC_GSS_KRB5_ENCTYPES_H
+#define _LINUX_SUNRPC_GSS_KRB5_ENCTYPES_H
+
+#ifdef CONFIG_SUNRPC_DISABLE_INSECURE_ENCTYPES
+
+/*
+ * NB: This list includes encryption types that were deprecated
+ * by RFC 8429 (DES3_CBC_SHA1 and ARCFOUR_HMAC).
+ *
+ * ENCTYPE_AES256_CTS_HMAC_SHA1_96
+ * ENCTYPE_AES128_CTS_HMAC_SHA1_96
+ * ENCTYPE_DES3_CBC_SHA1
+ * ENCTYPE_ARCFOUR_HMAC
+ */
+#define KRB5_SUPPORTED_ENCTYPES "18,17,16,23"
+
+#else   /* CONFIG_SUNRPC_DISABLE_INSECURE_ENCTYPES */
+
+/*
+ * NB: This list includes encryption types that were deprecated
+ * by RFC 8429 and RFC 6649.
+ *
+ * ENCTYPE_AES256_CTS_HMAC_SHA1_96
+ * ENCTYPE_AES128_CTS_HMAC_SHA1_96
+ * ENCTYPE_DES3_CBC_SHA1
+ * ENCTYPE_ARCFOUR_HMAC
+ * ENCTYPE_DES_CBC_MD5
+ * ENCTYPE_DES_CBC_CRC
+ * ENCTYPE_DES_CBC_MD4
  */
 #define KRB5_SUPPORTED_ENCTYPES "18,17,16,23,3,1,2"
+
+#endif  /* CONFIG_SUNRPC_DISABLE_INSECURE_ENCTYPES */
+
+#endif  /* _LINUX_SUNRPC_GSS_KRB5_ENCTYPES_H */
diff --git a/net/sunrpc/Kconfig b/net/sunrpc/Kconfig
index ac09ca803296..83f5617bae07 100644
--- a/net/sunrpc/Kconfig
+++ b/net/sunrpc/Kconfig
@@ -34,6 +34,22 @@ config RPCSEC_GSS_KRB5
 
           If unsure, say Y.
 
+config CONFIG_SUNRPC_DISABLE_INSECURE_ENCTYPES
+        bool "Secure RPC: Disable insecure Kerberos encryption types"
+        depends on RPCSEC_GSS_KRB5
+        default n
+        help
+          Choose Y here to disable the use of deprecated encryption types
+          with the Kerberos version 5 GSS-API mechanism (RFC 1964). The
+          deprecated encryption types include DES-CBC-MD5, DES-CBC-CRC,
+          and DES-CBC-MD4. These types were deprecated by RFC 6649 because
+          they were found to be insecure.
+
+          N is the default because many sites have deployed KDCs and
+          keytabs that contain only these deprecated encryption types.
+          Choosing Y prevents the use of known-insecure encryption types
+          but might result in compatibility problems.
+
 config SUNRPC_DEBUG
         bool "RPC: Enable dprintk debugging"
         depends on SUNRPC && SYSCTL
diff --git a/net/sunrpc/auth_gss/gss_krb5_mech.c b/net/sunrpc/auth_gss/gss_krb5_mech.c
index eab71fc7af3e..be31a58d54e0 100644
--- a/net/sunrpc/auth_gss/gss_krb5_mech.c
+++ b/net/sunrpc/auth_gss/gss_krb5_mech.c
@@ -53,6 +53,7 @@
 static struct gss_api_mech gss_kerberos_mech;   /* forward declaration */
 
 static const struct gss_krb5_enctype supported_gss_krb5_enctypes[] = {
+#ifndef CONFIG_SUNRPC_DISABLE_INSECURE_ENCTYPES
         /*
          * DES (All DES enctypes are mapped to the same gss functionality)
          */
@@ -74,6 +75,7 @@ static const struct gss_krb5_enctype supported_gss_krb5_enctypes[] = {
           .cksumlength = 8,
           .keyed_cksum = 0,
         },
+#endif  /* CONFIG_SUNRPC_DISABLE_INSECURE_ENCTYPES */
         /*
          * RC4-HMAC
          */