DNS: If the DNS server returns an error, allow that to be cached [ver #2]
[linux-3.10.git] / net / dns_resolver / dns_key.c
index 400a04d..739435a 100644 (file)
@@ -29,6 +29,7 @@
 #include <linux/kernel.h>
 #include <linux/keyctl.h>
 #include <linux/err.h>
+#include <linux/seq_file.h>
 #include <keys/dns_resolver-type.h>
 #include <keys/user-type.h>
 #include "internal.h"
@@ -43,6 +44,8 @@ MODULE_PARM_DESC(debug, "DNS Resolver debugging mask");
 
 const struct cred *dns_resolver_cache;
 
+#define        DNS_ERRORNO_OPTION      "dnserror"
+
 /*
  * Instantiate a user defined key for dns_resolver.
  *
@@ -59,9 +62,10 @@ static int
 dns_resolver_instantiate(struct key *key, const void *_data, size_t datalen)
 {
        struct user_key_payload *upayload;
+       unsigned long derrno;
        int ret;
        size_t result_len = 0;
-       const char *data = _data, *opt;
+       const char *data = _data, *end, *opt;
 
        kenter("%%%d,%s,'%s',%zu",
               key->serial, key->description, data, datalen);
@@ -71,13 +75,77 @@ dns_resolver_instantiate(struct key *key, const void *_data, size_t datalen)
        datalen--;
 
        /* deal with any options embedded in the data */
+       end = data + datalen;
        opt = memchr(data, '#', datalen);
        if (!opt) {
-               kdebug("no options currently supported");
-               return -EINVAL;
+               /* no options: the entire data is the result */
+               kdebug("no options");
+               result_len = datalen;
+       } else {
+               const char *next_opt;
+
+               result_len = opt - data;
+               opt++;
+               kdebug("options: '%s'", opt);
+               do {
+                       const char *eq;
+                       int opt_len, opt_nlen, opt_vlen, tmp;
+
+                       next_opt = memchr(opt, '#', end - opt) ?: end;
+                       opt_len = next_opt - opt;
+                       if (!opt_len) {
+                               printk(KERN_WARNING
+                                      "Empty option to dns_resolver key %d\n",
+                                      key->serial);
+                               return -EINVAL;
+                       }
+
+                       eq = memchr(opt, '=', opt_len) ?: end;
+                       opt_nlen = eq - opt;
+                       eq++;
+                       opt_vlen = next_opt - eq; /* will be -1 if no value */
+
+                       tmp = opt_vlen >= 0 ? opt_vlen : 0;
+                       kdebug("option '%*.*s' val '%*.*s'",
+                              opt_nlen, opt_nlen, opt, tmp, tmp, eq);
+
+                       /* see if it's an error number representing a DNS error
+                        * that's to be recorded as the result in this key */
+                       if (opt_nlen == sizeof(DNS_ERRORNO_OPTION) - 1 &&
+                           memcmp(opt, DNS_ERRORNO_OPTION, opt_nlen) == 0) {
+                               kdebug("dns error number option");
+                               if (opt_vlen <= 0)
+                                       goto bad_option_value;
+
+                               ret = strict_strtoul(eq, 10, &derrno);
+                               if (ret < 0)
+                                       goto bad_option_value;
+
+                               if (derrno < 1 || derrno > 511)
+                                       goto bad_option_value;
+
+                               kdebug("dns error no. = %lu", derrno);
+                               key->type_data.x[0] = -derrno;
+                               continue;
+                       }
+
+               bad_option_value:
+                       printk(KERN_WARNING
+                              "Option '%*.*s' to dns_resolver key %d:"
+                              " bad/missing value\n",
+                              opt_nlen, opt_nlen, opt, key->serial);
+                       return -EINVAL;
+               } while (opt = next_opt + 1, opt < end);
+       }
+
+       /* don't cache the result if we're caching an error saying there's no
+        * result */
+       if (key->type_data.x[0]) {
+               kleave(" = 0 [h_error %ld]", key->type_data.x[0]);
+               return 0;
        }
 
-       result_len = datalen;
+       kdebug("store result");
        ret = key_payload_reserve(key, result_len);
        if (ret < 0)
                return -EINVAL;
@@ -135,13 +203,27 @@ no_match:
        return ret;
 }
 
+/*
+ * Describe a DNS key
+ */
+static void dns_resolver_describe(const struct key *key, struct seq_file *m)
+{
+       int err = key->type_data.x[0];
+
+       seq_puts(m, key->description);
+       if (err)
+               seq_printf(m, ": %d", err);
+       else
+               seq_printf(m, ": %u", key->datalen);
+}
+
 struct key_type key_type_dns_resolver = {
        .name           = "dns_resolver",
        .instantiate    = dns_resolver_instantiate,
        .match          = dns_resolver_match,
        .revoke         = user_revoke,
        .destroy        = user_destroy,
-       .describe       = user_describe,
+       .describe       = dns_resolver_describe,
        .read           = user_read,
 };