[PATCH v2 2/5] nbd/server: Reject embedded NUL in NBD strings

[Eric Blake <eblake@redhat.com>]

The NBD spec is clear that any string sent from the client must not
contain embedded NUL characters.  If the client passes "a\0", we
should reject that option request rather than act on "a".

Testing this is not possible with a compliant client, but I was able
to use gdb to coerce libnbd into temporarily behaving as such a
client.

Signed-off-by: Eric Blake <eblake@redhat.com>
---
 nbd/server.c | 30 ++++++++++++++++++++----------
 1 file changed, 20 insertions(+), 10 deletions(-)

diff --git a/nbd/server.c b/nbd/server.c
index f74766add7b7..809f88ce6607 100644
--- a/nbd/server.c
+++ b/nbd/server.c
@@ -301,10 +301,11 @@ nbd_opt_invalid(NBDClient *client, Error **errp, const char *fmt, ...)
 }

 /* Read size bytes from the unparsed payload of the current option.
+ * If @check_nul, require that no NUL bytes appear in buffer.
  * Return -errno on I/O error, 0 if option was completely handled by
  * sending a reply about inconsistent lengths, or 1 on success. */
 static int nbd_opt_read(NBDClient *client, void *buffer, size_t size,
-                        Error **errp)
+                        bool check_nul, Error **errp)
 {
     if (size > client->optlen) {
         return nbd_opt_invalid(client, errp,
@@ -312,7 +313,16 @@ static int nbd_opt_read(NBDClient *client, void *buffer, size_t size,
                                nbd_opt_lookup(client->opt));
     }
     client->optlen -= size;
-    return qio_channel_read_all(client->ioc, buffer, size, errp) < 0 ? -EIO : 1;
+    if (qio_channel_read_all(client->ioc, buffer, size, errp) < 0) {
+        return -EIO;
+    }
+
+    if (check_nul && strnlen(buffer, size) != size) {
+        return nbd_opt_invalid(client, errp,
+                               "Unexpected embedded NUL in option %s",
+                               nbd_opt_lookup(client->opt));
+    }
+    return 1;
 }

 /* Drop size bytes from the unparsed payload of the current option.
@@ -349,7 +359,7 @@ static int nbd_opt_read_name(NBDClient *client, char **name, uint32_t *length,
     g_autofree char *local_name = NULL;

     *name = NULL;
-    ret = nbd_opt_read(client, &len, sizeof(len), errp);
+    ret = nbd_opt_read(client, &len, sizeof(len), false, errp);
     if (ret <= 0) {
         return ret;
     }
@@ -361,7 +371,7 @@ static int nbd_opt_read_name(NBDClient *client, char **name, uint32_t *length,
     }

     local_name = g_malloc(len + 1);
-    ret = nbd_opt_read(client, local_name, len, errp);
+    ret = nbd_opt_read(client, local_name, len, true, errp);
     if (ret <= 0) {
         return ret;
     }
@@ -576,14 +586,14 @@ static int nbd_negotiate_handle_info(NBDClient *client, Error **errp)
     }
     trace_nbd_negotiate_handle_export_name_request(name);

-    rc = nbd_opt_read(client, &requests, sizeof(requests), errp);
+    rc = nbd_opt_read(client, &requests, sizeof(requests), false, errp);
     if (rc <= 0) {
         return rc;
     }
     requests = be16_to_cpu(requests);
     trace_nbd_negotiate_handle_info_requests(requests);
     while (requests--) {
-        rc = nbd_opt_read(client, &request, sizeof(request), errp);
+        rc = nbd_opt_read(client, &request, sizeof(request), false, errp);
         if (rc <= 0) {
             return rc;
         }
@@ -806,7 +816,7 @@ static int nbd_meta_pattern(NBDClient *client, const char *pattern, bool *match,
     assert(len);

     query = g_malloc(len);
-    ret = nbd_opt_read(client, query, len, errp);
+    ret = nbd_opt_read(client, query, len, true, errp);
     if (ret <= 0) {
         g_free(query);
         return ret;
@@ -943,7 +953,7 @@ static int nbd_negotiate_meta_query(NBDClient *client,
     char ns[5];
     uint32_t len;

-    ret = nbd_opt_read(client, &len, sizeof(len), errp);
+    ret = nbd_opt_read(client, &len, sizeof(len), false, errp);
     if (ret <= 0) {
         return ret;
     }
@@ -959,7 +969,7 @@ static int nbd_negotiate_meta_query(NBDClient *client,
     }

     len -= ns_len;
-    ret = nbd_opt_read(client, ns, ns_len, errp);
+    ret = nbd_opt_read(client, ns, ns_len, true, errp);
     if (ret <= 0) {
         return ret;
     }
@@ -1016,7 +1026,7 @@ static int nbd_negotiate_meta_queries(NBDClient *client,
                             "export '%s' not present", sane_name);
     }

-    ret = nbd_opt_read(client, &nb_queries, sizeof(nb_queries), errp);
+    ret = nbd_opt_read(client, &nb_queries, sizeof(nb_queries), false, errp);
     if (ret <= 0) {
         return ret;
     }
-- 
2.28.0