KEYS: Add a key type op to permit the key description to be vetted

Add a key type operation to permit the key type to vet the description of a new
key that key_alloc() is about to allocate.  The operation may reject the
description if it wishes with an error of its choosing.  If it does this, the
key will not be allocated.

Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-by: Mimi Zohar <zohar@us.ibm.com>
Signed-off-by: James Morris <jmorris@namei.org>

4 files changed, 37 insertions, 0 deletions

diff --git a/Documentation/keys.txt b/Documentation/keys.txt
index e4dbbdb1bd96..cf68d1fed95d 100644
--- a/Documentation/keys.txt
+++ b/Documentation/keys.txt
@@ -1062,6 +1062,13 @@ The structure has a number of fields, some of which are mandatory:
      viable.
 
 
+ (*) int (*vet_description)(const char *description);
+
+     This optional method is called to vet a key description.  If the key type
+     doesn't approve of the key description, it may return an error, otherwise
+     it should return 0.
+
+
  (*) int (*instantiate)(struct key *key, const void *data, size_t datalen);
 
      This method is called to attach a payload to a key during construction.
diff --git a/include/linux/key-type.h b/include/linux/key-type.h
index 65833d4d5998..fc8525e838b7 100644
--- a/include/linux/key-type.h
+++ b/include/linux/key-type.h
@@ -41,6 +41,9 @@ struct key_type {
          */
         size_t def_datalen;
 
+        /* vet a description */
+        int (*vet_description)(const char *description);
+
         /* instantiate a key of this type
          * - this method should call key_payload_reserve() to determine if the
          *   user's quota will hold the payload
diff --git a/net/rxrpc/ar-key.c b/net/rxrpc/ar-key.c
index d763793d39de..43ea7de2fc8e 100644
--- a/net/rxrpc/ar-key.c
+++ b/net/rxrpc/ar-key.c
@@ -25,6 +25,7 @@
 #include <keys/user-type.h>
 #include "ar-internal.h"
 
+static int rxrpc_vet_description_s(const char *);
 static int rxrpc_instantiate(struct key *, const void *, size_t);
 static int rxrpc_instantiate_s(struct key *, const void *, size_t);
 static void rxrpc_destroy(struct key *);
@@ -52,6 +53,7 @@ EXPORT_SYMBOL(key_type_rxrpc);
  */
 struct key_type key_type_rxrpc_s = {
         .name           = "rxrpc_s",
+        .vet_description = rxrpc_vet_description_s,
         .instantiate    = rxrpc_instantiate_s,
         .match          = user_match,
         .destroy        = rxrpc_destroy_s,
@@ -59,6 +61,23 @@ struct key_type key_type_rxrpc_s = {
 };
 
 /*
+ * Vet the description for an RxRPC server key
+ */
+static int rxrpc_vet_description_s(const char *desc)
+{
+        unsigned long num;
+        char *p;
+
+        num = simple_strtoul(desc, &p, 10);
+        if (*p != ':' || num > 65535)
+                return -EINVAL;
+        num = simple_strtoul(p + 1, &p, 10);
+        if (*p || num < 1 || num > 255)
+                return -EINVAL;
+        return 0;
+}
+
+/*
  * parse an RxKAD type XDR format token
  * - the caller guarantees we have at least 4 words
  */
diff --git a/security/keys/key.c b/security/keys/key.c
index 1c2d43dc5107..8e315ef2e88e 100644
--- a/security/keys/key.c
+++ b/security/keys/key.c
@@ -249,6 +249,14 @@ struct key *key_alloc(struct key_type *type, const char *desc,
         if (!desc || !*desc)
                 goto error;
 
+        if (type->vet_description) {
+                ret = type->vet_description(desc);
+                if (ret < 0) {
+                        key = ERR_PTR(ret);
+                        goto error;
+                }
+        }
+
         desclen = strlen(desc) + 1;
         quotalen = desclen + type->def_datalen;