tbd: BUCKET(-1) returns wrong offset because tdb->hash_size is an unsigned int

tbd: BUCKET(-1) returns wrong offset because tdb->hash_size is an unsigned int

The following C program demonstrates the issue:

  #include <stdio.h>
  #include <stdlib.h>
  #include <stdarg.h>
  #include <stdbool.h>
  #include <string.h>
  #include <unistd.h>
  #include <errno.h>
  #include <dirent.h>
  #include <sys/types.h>

  int main(int argc, char **argv)
  {
      int hash = -1;
      int tsize_signed = 10;
      unsigned int tsize_unsigned = 10;
      int bucket;

  #define BUCKET(hash, tsize) ((hash) % (tsize))

      bucket = BUCKET(hash, tsize_unsigned);
      printf("hash [%d] tsize [%d] bucket [%d]\n", hash, tsize_unsigned, bucket);

      bucket = BUCKET(hash, tsize_signed);
      printf("hash [%d] tsize [%d] bucket [%d]\n", hash, tsize_signed, bucket);

      return 0;
  }

Output:

$ ./tmp
hash [-1] tsize [10] bucket [5]
hash [-1] tsize [10] bucket [-1]

The first version is what the current BUCKET() macro does. As a result
we lock the hashtable chain in bucket 5, NOT the freelist.

-1 is sign converted to an unsigned int 4294967295 and

  4294967295 % 10 = 5.

As all callers will lock the same wrong list consistently locking is
still consistent.

Stumpled across this when looking at the output of `tdbtool DB list`
which always printed some other hashchain and not the freelist.

The freelist bucket offset computation doesn't use the BUCKET macro in
freelist.c (directly or indirectly) when working on the freelist, it
just directly uses the FREELIST_TOP define, so this problem only affects
tdbtool list.

Signed-off-by: Ralph Boehme <slow@samba.org>
Reviewed-by: Jeremy Allison <jra@samba.org>