From 589f7d1e4f3aaca3fec6c38474bb962a9c578ebe Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Toke=20H=C3=B8iland-J=C3=B8rgensen?= <toke@toke.dk>
Date: Thu, 15 Apr 2021 04:38:49 +0200
Subject: [PATCH] Nest: Allow MAC algorithms to specify min/max key length

Add min/max key length fields to the MAC algorithm description and
validate configured keys before they are used.
---
 lib/mac.c       |  2 +-
 lib/mac.h       |  2 ++
 nest/config.Y   |  9 +++++++--
 nest/password.c | 26 ++++++++++++++++++++++++++
 nest/password.h |  1 +
 5 files changed, 37 insertions(+), 3 deletions(-)

diff --git a/lib/mac.c b/lib/mac.c
index f07d38df..6c9cc743 100644
--- a/lib/mac.c
+++ b/lib/mac.c
@@ -173,7 +173,7 @@ hmac_final(struct mac_context *ctx)
   {									\
     name, size/8, sizeof(struct vx##_context),				\
     vx##_mac_init, vx##_mac_update, vx##_mac_final,			\
-    size/8, VX##_BLOCK_SIZE, NULL, NULL, NULL				\
+    size/8, VX##_BLOCK_SIZE, NULL, NULL, NULL, 0, VX##_SIZE		\
   }
 
 const struct mac_desc mac_table[ALG_MAX] = {
diff --git a/lib/mac.h b/lib/mac.h
index a03e0546..99a56eed 100644
--- a/lib/mac.h
+++ b/lib/mac.h
@@ -94,6 +94,8 @@ struct mac_desc {
   void (*hash_init)(struct hash_context *ctx);
   void (*hash_update)(struct hash_context *ctx, const byte *data, uint datalen);
   byte *(*hash_final)(struct hash_context *ctx);
+  uint min_key_length;			/* Minimum allowed key length */
+  uint max_key_length;			/* Maximum allowed key length */
 };
 
 extern const struct mac_desc mac_table[ALG_MAX];
diff --git a/nest/config.Y b/nest/config.Y
index 8bd89de0..45d18679 100644
--- a/nest/config.Y
+++ b/nest/config.Y
@@ -504,8 +504,8 @@ password_items:
 ;
 
 password_item:
-    password_item_begin '{' password_item_params '}'
-  | password_item_begin
+    password_item_begin '{' password_item_params '}' password_item_end
+  | password_item_begin password_item_end
 ;
 
 password_item_begin:
@@ -542,6 +542,11 @@ password_algorithm:
  | BLAKE2B512	{ $$ = ALG_BLAKE2B_512; }
  ;
 
+password_item_end:
+{
+  password_validate_length(this_p_item);
+};
+
 
 /* BFD options */
 
diff --git a/nest/password.c b/nest/password.c
index 6f87af21..34e2a61e 100644
--- a/nest/password.c
+++ b/nest/password.c
@@ -9,6 +9,7 @@
 
 #include "nest/bird.h"
 #include "nest/password.h"
+#include "conf/conf.h"
 #include "lib/string.h"
 #include "lib/timer.h"
 #include "lib/mac.h"
@@ -85,3 +86,28 @@ max_mac_length(list *l)
 
   return val;
 }
+
+/**
+ * password_validate_length - enforce key length restrictions
+ * @pi: Password item
+ *
+ * This is a common MAC algorithm validation function that will enforce that the
+ * key length constrains specified in the MAC type table.
+ */
+
+void
+password_validate_length(const struct password_item *pi)
+{
+  if (!pi->alg)
+    return;
+
+  const struct mac_desc *alg = &mac_table[pi->alg];
+
+  if (alg->min_key_length && (pi->length < alg->min_key_length))
+    cf_error("Key length (%u B) below minimum length of %u B for %s",
+             pi->length, alg->min_key_length, alg->name);
+
+  if (alg->max_key_length && (pi->length > alg->max_key_length))
+    cf_error("Key length (%u B) exceeds maximum length of %u B for %s",
+             pi->length, alg->max_key_length, alg->name);
+}
diff --git a/nest/password.h b/nest/password.h
index 8a0da223..53168bb7 100644
--- a/nest/password.h
+++ b/nest/password.h
@@ -24,6 +24,7 @@ extern struct password_item *last_password_item;
 struct password_item *password_find(list *l, int first_fit);
 struct password_item *password_find_by_id(list *l, uint id);
 struct password_item *password_find_by_value(list *l, char *pass, uint size);
+void password_validate_length(const struct password_item *p);
 
 static inline int password_verify(struct password_item *p1, char *p2, uint size)
 {