3 files changed, 96 insertions, 5 deletions

diff --git a/fs/afs/cell.c b/fs/afs/cell.c
index ffea35c63879..d0765883430e 100644
--- a/fs/afs/cell.c
+++ b/fs/afs/cell.c
@@ -73,6 +73,10 @@ static struct afs_cell *afs_cell_alloc(const char *name, char *vllist)
         if (!vllist || strlen(vllist) < 7) {
                 ret = dns_query("afsdb", name, namelen, "ipv4", &dvllist, NULL);
                 if (ret < 0) {
+                        if (ret == -ENODATA || ret == -EAGAIN || ret == -ENOKEY)
+                                /* translate these errors into something
+                                 * userspace might understand */
+                                ret = -EDESTADDRREQ;
                         _leave(" = %d", ret);
                         return ERR_PTR(ret);
                 }
diff --git a/net/dns_resolver/dns_key.c b/net/dns_resolver/dns_key.c
index 400a04d5c9a1..739435a6af39 100644
--- a/net/dns_resolver/dns_key.c
+++ b/net/dns_resolver/dns_key.c
@@ -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,
 };
 
diff --git a/net/dns_resolver/dns_query.c b/net/dns_resolver/dns_query.c
index 03d5255f5cf2..c32be292c7e3 100644
--- a/net/dns_resolver/dns_query.c
+++ b/net/dns_resolver/dns_query.c
@@ -136,6 +136,11 @@ int dns_query(const char *type, const char *name, size_t namelen,
         if (ret < 0)
                 goto put;
 
+        /* If the DNS server gave an error, return that to the caller */
+        ret = rkey->type_data.x[0];
+        if (ret)
+                goto put;
+
         upayload = rcu_dereference_protected(rkey->payload.data,
                                              lockdep_is_held(&rkey->sem));
         len = upayload->datalen;