Don't overwrite tdbs with different version numbers.

In future, this may happen, and we don't want to clobber them.

ccan/tdb/open.c

@@ -247,17 +247,19 @@ struct tdb_context *tdb_open_ex(const char *name, int hash_size, int tdb_flags,
 
 	errno = 0;
 	if (read(tdb->fd, &tdb->header, sizeof(tdb->header)) != sizeof(tdb->header)
-	    || strcmp(tdb->header.magic_food, TDB_MAGIC_FOOD) != 0
-	    || (tdb->header.version != TDB_VERSION
-		&& !(rev = (tdb->header.version==TDB_BYTEREV(TDB_VERSION))))) {
-		/* its not a valid database - possibly initialise it */
+	    || strcmp(tdb->header.magic_food, TDB_MAGIC_FOOD) != 0) {
 		if (!(open_flags & O_CREAT) || tdb_new_database(tdb, hash_size) == -1) {
 			if (errno == 0) {
-			errno = EIO; /* ie bad format or something */
+				errno = EIO; /* ie bad format or something */
 			}
 			goto fail;
 		}
 		rev = (tdb->flags & TDB_CONVERT);
+	} else if (tdb->header.version != TDB_VERSION
+		   && !(rev = (tdb->header.version==TDB_BYTEREV(TDB_VERSION)))) {
+		/* wrong version */
+		errno = EIO;
+		goto fail;
 	}
 	vp = (unsigned char *)&tdb->header.version;
 	vertest = (((uint32_t)vp[0]) << 24) | (((uint32_t)vp[1]) << 16) |

ccan/tdb/test/run-bad-tdb-header.c

@@ -0,0 +1,54 @@
+#define _XOPEN_SOURCE 500
+#include "tdb/tdb.h"
+#include "tdb/io.c"
+#include "tdb/tdb.c"
+#include "tdb/lock.c"
+#include "tdb/freelist.c"
+#include "tdb/traverse.c"
+#include "tdb/transaction.c"
+#include "tdb/error.c"
+#include "tdb/open.c"
+#include "tap/tap.h"
+#include <stdlib.h>
+#include <err.h>
+
+int main(int argc, char *argv[])
+{
+	struct tdb_context *tdb;
+	struct tdb_header hdr;
+	int fd;
+
+	plan_tests(11);
+	/* Can open fine if complete crap, as long as O_CREAT. */
+	fd = open("/tmp/test.tdb", O_RDWR|O_CREAT|O_TRUNC, 0600);
+	ok1(fd >= 0);
+	ok1(write(fd, "hello world", 11) == 11);
+	close(fd);
+	tdb = tdb_open("/tmp/test.tdb", 1024, 0, O_RDWR, 0);
+	ok1(!tdb);
+	tdb = tdb_open("/tmp/test.tdb", 1024, 0, O_CREAT|O_RDWR, 0600);
+	ok1(tdb);
+	tdb_close(tdb);
+
+	/* Now, with wrong version it should *not* overwrite. */
+	fd = open("/tmp/test.tdb", O_RDWR);
+	ok1(fd >= 0);
+	ok1(read(fd, &hdr, sizeof(hdr)) == sizeof(hdr));
+	ok1(hdr.version == TDB_VERSION);
+	hdr.version++;
+	lseek(fd, 0, SEEK_SET);
+	ok1(write(fd, &hdr, sizeof(hdr)) == sizeof(hdr));
+	close(fd);
+
+	tdb = tdb_open("/tmp/test.tdb", 1024, 0, O_RDWR|O_CREAT, 0600);
+	ok1(errno == EIO);
+	ok1(!tdb);
+
+	/* With truncate, will be fine. */
+	tdb = tdb_open("/tmp/test.tdb", 1024, 0, O_RDWR|O_CREAT|O_TRUNC, 0600);
+	ok1(tdb);
+	tdb_close(tdb);
+	unlink("/tmp/test.tdb");
+
+	return exit_status();
+}