librbd: prevent creation of v2 image ids that are too large

The librbd API is capped at 24 characters for expressing the
object prefix for data blocks (including trailing null byte).

Fixes: http://tracker.ceph.com/issues/16887
Signed-off-by: Jason Dillaman <dillaman@redhat.com>
(cherry picked from commit 4de7c8d0a7222c83268d03b99015c6b9d25f124d)

diff --git a/src/librbd/internal.cc b/src/librbd/internal.cc
index f4b110eea8ce0c37c2780e1429cfd527f88e7882..7bd9e665aa51983312ceca318b428121560bc2f4 100644 (file)
--- a/src/librbd/internal.cc
+++ b/src/librbd/internal.cc
@@ -1029,6 +1029,14 @@ reprotect_and_return_err:
     extra = rand() % 0xFFFFFFFF;
     bid_ss << std::hex << bid << std::hex << extra;
     id = bid_ss.str();
+
+    // ensure the image id won't overflow the fixed block name size
+    const size_t max_id_length = RBD_MAX_BLOCK_NAME_SIZE -
+                                 strlen(RBD_DATA_PREFIX) - 1;
+    if (id.length() > max_id_length) {
+      id = id.substr(id.length() - max_id_length);
+    }
+
     r = cls_client::set_id(&io_ctx, id_obj, id);
     if (r < 0) {
       lderr(cct) << "error setting image id: " << cpp_strerror(r) << dendl;