[Devel] [PATCH hci-8.1] dm-ploop: fix u32 overflow of the delta BAT byte size

[Konstantin Khorenko]

  Applied with two small changes on commit, no need to resend.

  1. Added

  Fixes: 6ddad5a4d226 ("dm-ploop: Add ploop target driver")

  2. Changed the message of the new check in ploop_resize(). After the
  patch the function prints the same text from two different checks:

          } else if (SEC_TO_CLU(ploop, new_sectors) >= U32_MAX - 2) {
                  DMWARN("resize: too large size is requested");
                  return -EINVAL;
          ...
          nr_bat_entries = SEC_TO_CLU(ploop, new_sectors);
          nr_bat_clusters = ploop_nr_bat_clusters(ploop, nr_bat_entries);
          if ((u64)nr_bat_clusters + nr_bat_entries > PLOOP_MAX_HB_NR) {
                  DMWARN("resize: too large size is requested");
                  return -EINVAL;
          }

  Both checks are needed: the first one runs on sector_t and guards the
  u32 truncation of nr_bat_entries, the second one bounds hb_nr. But with
  the same text the log does not tell which one fired, and the first check
  looks redundant next to the second one. So the new check now says what
  does not fit, matching "Too large BAT" in ploop_setup_metadata():

                  DMWARN("resize: too large BAT");

--
Best regards,

Konstantin Khorenko,
Virtuozzo Linux Kernel Team