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 d3f1cd3fb714f67a79843cadd9fbbbfd1a358729..9e1112c72c73edf201ecafcaa1af17e9fe972eef 100644 (file)
--- a/src/librbd/internal.cc
+++ b/src/librbd/internal.cc
@@ -1048,6 +1048,14 @@ int mirror_image_disable_internal(ImageCtx *ictx, bool force,
     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;