tdb: put example hashes into header, so we notice incorrect hash_fn.

This is Stefan Metzmacher <metze@samba.org>'s patch with minor changes:
1) Use the TDB_MAGIC constant so both hashes aren't of strings.
2) Check the hash in tdb_check (paranoia, really).
3) Additional check in the (unlikely!) case where both examples hash to 0.
4) Cosmetic changes to var names and complaint message.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

3 files changed, 65 insertions, 2 deletions

diff --git a/lib/tdb/common/check.c b/lib/tdb/common/check.c
index fd3c0a91f3..b1b98d4f1e 100644
--- a/lib/tdb/common/check.c
+++ b/lib/tdb/common/check.c
@@ -28,6 +28,7 @@
 static bool tdb_check_header(struct tdb_context *tdb, tdb_off_t *recovery)
 {
 	struct tdb_header hdr;
+	uint32_t h1, h2;
 
 	if (tdb->methods->tdb_read(tdb, 0, &hdr, sizeof(hdr), 0) == -1)
 		return false;
@@ -41,6 +42,11 @@ static bool tdb_check_header(struct tdb_context *tdb, tdb_off_t *recovery)
 	if (hdr.rwlocks != 0)
 		goto corrupt;
 
+	tdb_header_hash(tdb, &h1, &h2);
+	if (hdr.magic1_hash && hdr.magic2_hash &&
+	    (hdr.magic1_hash != h1 || hdr.magic2_hash != h2))
+		goto corrupt;
+
 	if (hdr.hash_size == 0)
 		goto corrupt;
 
diff --git a/lib/tdb/common/open.c b/lib/tdb/common/open.c
index 7687ff6e32..401fa74ae0 100644
--- a/lib/tdb/common/open.c
+++ b/lib/tdb/common/open.c
@@ -44,6 +44,25 @@ static unsigned int default_tdb_hash(TDB_DATA *key)
 	return (1103515243 * value + 12345);  
 }
 
+/* We use two hashes to double-check they're using the right hash function. */
+void tdb_header_hash(struct tdb_context *tdb,
+		     uint32_t *magic1_hash, uint32_t *magic2_hash)
+{
+	TDB_DATA hash_key;
+	uint32_t tdb_magic = TDB_MAGIC;
+
+	hash_key.dptr = (unsigned char *)TDB_MAGIC_FOOD;
+	hash_key.dsize = sizeof(TDB_MAGIC_FOOD);
+	*magic1_hash = tdb->hash_fn(&hash_key);
+
+	hash_key.dptr = CONVERT(tdb_magic);
+	hash_key.dsize = sizeof(tdb_magic);
+	*magic2_hash = tdb->hash_fn(&hash_key);
+
+	/* Make sure at least one hash is non-zero! */
+	if (*magic1_hash == 0 && *magic2_hash == 0)
+		*magic1_hash = 1;
+}
 
 /* initialise a new database with a specified hash size */
 static int tdb_new_database(struct tdb_context *tdb, int hash_size)
@@ -62,6 +81,9 @@ static int tdb_new_database(struct tdb_context *tdb, int hash_size)
 	/* Fill in the header */
 	newdb->version = TDB_VERSION;
 	newdb->hash_size = hash_size;
+
+	tdb_header_hash(tdb, &newdb->magic1_hash, &newdb->magic2_hash);
+
 	if (tdb->flags & TDB_INTERNAL) {
 		tdb->map_size = size;
 		tdb->map_ptr = (char *)newdb;
@@ -140,6 +162,9 @@ struct tdb_context *tdb_open_ex(const char *name, int hash_size, int tdb_flags,
 	unsigned char *vp;
 	uint32_t vertest;
 	unsigned v;
+	uint32_t magic1_hash;
+	uint32_t magic2_hash;
+	const char *hash_alg;
 
 	if (!(tdb = (struct tdb_context *)calloc(1, sizeof *tdb))) {
 		/* Can't log this */
@@ -161,7 +186,14 @@ struct tdb_context *tdb_open_ex(const char *name, int hash_size, int tdb_flags,
 		tdb->log.log_fn = null_log_fn;
 		tdb->log.log_private = NULL;
 	}
-	tdb->hash_fn = hash_fn ? hash_fn : default_tdb_hash;
+
+	if (hash_fn) {
+		tdb->hash_fn = hash_fn;
+		hash_alg = "user defined";
+	} else {
+		tdb->hash_fn = default_tdb_hash;
+		hash_alg = "default";
+	}
 
 	/* cache the page size */
 	tdb->page_size = getpagesize();
@@ -279,6 +311,27 @@ struct tdb_context *tdb_open_ex(const char *name, int hash_size, int tdb_flags,
 		goto fail;
 	}
 
+	tdb_header_hash(tdb, &magic1_hash, &magic2_hash);
+
+	if ((tdb->header.magic1_hash == 0) && (tdb->header.magic2_hash == 0)) {
+		/* older TDB without magic hash references */
+	} else if ((tdb->header.magic1_hash != magic1_hash) ||
+		   (tdb->header.magic2_hash != magic2_hash)) {
+		TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_open_ex: "
+			 "%s was not created with the %s hash function we are using\n"
+			 "magic1_hash[0x%08X %s 0x%08X] "
+			 "magic2_hash[0x%08X %s 0x%08X]\n",
+			 name, hash_alg,
+			 tdb->header.magic1_hash,
+			 (tdb->header.magic1_hash == magic1_hash) ? "==" : "!=",
+			 magic1_hash,
+			 tdb->header.magic2_hash,
+			 (tdb->header.magic2_hash == magic2_hash) ? "==" : "!=",
+			 magic2_hash));
+		errno = EINVAL;
+		goto fail;
+	}
+
 	/* Is it already in the open list?  If so, fail. */
 	if (tdb_already_open(st.st_dev, st.st_ino)) {
 		TDB_LOG((tdb, TDB_DEBUG_ERROR, "tdb_open_ex: "
diff --git a/lib/tdb/common/tdb_private.h b/lib/tdb/common/tdb_private.h
index 9d0f3bcd70..eccd6880ef 100644
--- a/lib/tdb/common/tdb_private.h
+++ b/lib/tdb/common/tdb_private.h
@@ -147,7 +147,9 @@ struct tdb_header {
 	tdb_off_t rwlocks; /* obsolete - kept to detect old formats */
 	tdb_off_t recovery_start; /* offset of transaction recovery region */
 	tdb_off_t sequence_number; /* used when TDB_SEQNUM is set */
-	tdb_off_t reserved[29];
+	uint32_t magic1_hash; /* hash of TDB_MAGIC_FOOD. */
+	uint32_t magic2_hash; /* hash of TDB_MAGIC. */
+	tdb_off_t reserved[27];
 };
 
 struct tdb_lock_type {
@@ -268,3 +270,5 @@ int tdb_rec_free_read(struct tdb_context *tdb, tdb_off_t off,
 		      struct tdb_record *rec);
 bool tdb_write_all(int fd, const void *buf, size_t count);
 int tdb_transaction_recover(struct tdb_context *tdb);
+void tdb_header_hash(struct tdb_context *tdb,
+		     uint32_t *magic1_hash, uint32_t *magic2_hash);