2 files changed, 25 insertions, 4 deletions

diff --git a/Documentation/networking/dns_resolver.txt b/Documentation/networking/dns_resolver.txt
index aefd1e681804..04ca06325b08 100644
--- a/Documentation/networking/dns_resolver.txt
+++ b/Documentation/networking/dns_resolver.txt
@@ -61,7 +61,6 @@ before the more general line given above as the first match is the one taken.
         create  dns_resolver    foo:*   *       /usr/sbin/dns.foo %k
 
 
-
 =====
 USAGE
 =====
@@ -104,6 +103,14 @@ implemented in the module can be called after doing:
      returned also.
 
 
+===============================
+READING DNS KEYS FROM USERSPACE
+===============================
+
+Keys of dns_resolver type can be read from userspace using keyctl_read() or
+"keyctl read/print/pipe".
+
+
 =========
 MECHANISM
 =========
diff --git a/net/dns_resolver/dns_key.c b/net/dns_resolver/dns_key.c
index 739435a6af39..cfa7a5e1c5c9 100644
--- a/net/dns_resolver/dns_key.c
+++ b/net/dns_resolver/dns_key.c
@@ -67,8 +67,9 @@ dns_resolver_instantiate(struct key *key, const void *_data, size_t datalen)
         size_t result_len = 0;
         const char *data = _data, *end, *opt;
 
-        kenter("%%%d,%s,'%s',%zu",
-               key->serial, key->description, data, datalen);
+        kenter("%%%d,%s,'%*.*s',%zu",
+               key->serial, key->description,
+               (int)datalen, (int)datalen, data, datalen);
 
         if (datalen <= 1 || !data || data[datalen - 1] != '\0')
                 return -EINVAL;
@@ -217,6 +218,19 @@ static void dns_resolver_describe(const struct key *key, struct seq_file *m)
                 seq_printf(m, ": %u", key->datalen);
 }
 
+/*
+ * read the DNS data
+ * - the key's semaphore is read-locked
+ */
+static long dns_resolver_read(const struct key *key,
+                              char __user *buffer, size_t buflen)
+{
+        if (key->type_data.x[0])
+                return key->type_data.x[0];
+
+        return user_read(key, buffer, buflen);
+}
+
 struct key_type key_type_dns_resolver = {
         .name           = "dns_resolver",
         .instantiate    = dns_resolver_instantiate,
@@ -224,7 +238,7 @@ struct key_type key_type_dns_resolver = {
         .revoke         = user_revoke,
         .destroy        = user_destroy,
         .describe       = dns_resolver_describe,
-        .read           = user_read,
+        .read           = dns_resolver_read,
 };
 
 static int __init init_dns_resolver(void)