r6528: - in tdb_fetch() we effectively disallowed zero length records by

  returning NULL/0, which is the same as we used for a failure. Having
  to look at tdb->ecode (which we never do) is too error prone.

  Instead, tdb_fetch() should behave like malloc() and talloc(), where
  zero length is not special and malloc(0) returns a valid pointer.

- similarly in data_blob(), asking for data_blob(NULL, 0) should
  return a zero blob, but asking for data_blob(ptr, 0) should return a
  zero length blob with a valid pointer, just like talloc() and malloc()

This change fixes the SummaryInformation stream stored in the tdb
backend when manipulated from w2k. The w2k client was using
SET_EOF_INFORMATION to create a zero-length stream, which we return
STATUS_NOT_FOUND on, as the tdb_fetch() gave us back a NULL/0 blob,
which we returned as not-found
(This used to be commit 162bbe4402b9de6ac06103df904b9fc204fbff29)

2 files changed, 5 insertions, 8 deletions

diff --git a/source4/lib/data_blob.c b/source4/lib/data_blob.c
index 284db4518f..2ec21717b1 100644
--- a/source4/lib/data_blob.c
+++ b/source4/lib/data_blob.c
@@ -29,7 +29,7 @@ DATA_BLOB data_blob_named(const void *p, size_t length, const char *name)
 {
 	DATA_BLOB ret;
 
-	if (length == 0) {
+	if (p == NULL && length == 0) {
 		ZERO_STRUCT(ret);
 		return ret;
 	}
diff --git a/source4/lib/tdb/common/tdb.c b/source4/lib/tdb/common/tdb.c
index 6554ec5697..670fdda7cd 100644
--- a/source4/lib/tdb/common/tdb.c
+++ b/source4/lib/tdb/common/tdb.c
@@ -1129,8 +1129,8 @@ static int tdb_update_hash(TDB_CONTEXT *tdb, TDB_DATA key, u32 hash, TDB_DATA db
 /* find an entry in the database given a key */
 /* If an entry doesn't exist tdb_err will be set to
  * TDB_ERR_NOEXIST. If a key has no data attached
- * tdb_err will not be set. Both will return a
- * zero pptr and zero dsize.
+ * then the TDB_DATA will have zero length but
+ * a non-zero pointer
  */
 
 TDB_DATA tdb_fetch(TDB_CONTEXT *tdb, TDB_DATA key)
@@ -1145,11 +1145,8 @@ TDB_DATA tdb_fetch(TDB_CONTEXT *tdb, TDB_DATA key)
 	if (!(rec_ptr = tdb_find_lock_hash(tdb,key,hash,F_RDLCK,&rec)))
 		return tdb_null;
 
-	if (rec.data_len)
-		ret.dptr = tdb_alloc_read(tdb, rec_ptr + sizeof(rec) + rec.key_len,
-					  rec.data_len);
-	else
-		ret.dptr = NULL;
+	ret.dptr = tdb_alloc_read(tdb, rec_ptr + sizeof(rec) + rec.key_len,
+				  rec.data_len);
 	ret.dsize = rec.data_len;
 	tdb_unlock(tdb, BUCKET(rec.full_hash), F_RDLCK);
 	return ret;