From: Gary Lockyer <gary@catalyst.net.nz>
Date: Thu, 22 Mar 2018 22:27:10 +0000 (+1300)
Subject: ldb_tdb: Do not make search or DB modifications without a lock
X-Git-Tag: ldb-1.4.0~450
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=501b35f86199216c78e38b4e0bc8e985e417f95d;p=thirdparty%2Fsamba.git

ldb_tdb: Do not make search or DB modifications without a lock

The ldb_cache startup code would previously not take a read lock
nor a sufficiently wide write transaction.

The new code takes a read lock, and if it needs to write takes a
write lock (transaction) and re-reads before continuing.

Signed-off-by: Gary Lockyer <gary@catalyst.net.nz>
Signed-off-by: Andrew Bartlett <abartlet@samba.org>
---

diff --git a/lib/ldb/ldb_tdb/ldb_cache.c b/lib/ldb/ldb_tdb/ldb_cache.c
index 4790bcd7e53..a9d2113e707 100644
--- a/lib/ldb/ldb_tdb/ldb_cache.c
+++ b/lib/ldb/ldb_tdb/ldb_cache.c
@@ -386,6 +386,7 @@ int ltdb_cache_load(struct ldb_module *module)
 	uint64_t seq;
 	struct ldb_message *baseinfo = NULL, *options = NULL;
 	const struct ldb_schema_attribute *a;
+	bool have_write_txn = false;
 	int r;
 
 	ldb = ldb_module_get_ctx(module);
@@ -406,29 +407,38 @@ int ltdb_cache_load(struct ldb_module *module)
 	baseinfo_dn = ldb_dn_new(baseinfo, ldb, LTDB_BASEINFO);
 	if (baseinfo_dn == NULL) goto failed;
 
+	r = ltdb->kv_ops->lock_read(module);
+	if (r != LDB_SUCCESS) {
+		goto failed;
+	}
 	r= ltdb_search_dn1(module, baseinfo_dn, baseinfo, 0);
 	if (r != LDB_SUCCESS && r != LDB_ERR_NO_SUCH_OBJECT) {
-		goto failed;
+		goto failed_and_unlock;
 	}
-	
+
 	/* possibly initialise the baseinfo */
 	if (r == LDB_ERR_NO_SUCH_OBJECT) {
 
+		/* Give up the read lock, try again with a write lock */
+		r = ltdb->kv_ops->unlock_read(module);
+		if (r != LDB_SUCCESS) {
+			goto failed;
+		}
+
 		if (ltdb->kv_ops->begin_write(ltdb) != 0) {
 			goto failed;
 		}
 
+		have_write_txn = true;
+
 		/* error handling for ltdb_baseinfo_init() is by
 		   looking for the record again. */
 		ltdb_baseinfo_init(module);
 
-		if (ltdb->kv_ops->finish_write(ltdb) != 0) {
-			goto failed;
-		}
-
 		if (ltdb_search_dn1(module, baseinfo_dn, baseinfo, 0) != LDB_SUCCESS) {
-			goto failed;
+			goto failed_and_unlock;
 		}
+
 	}
 
 	/* Ignore the result, and update the sequence number */
@@ -443,16 +453,17 @@ int ltdb_cache_load(struct ldb_module *module)
 	ltdb->sequence_number = seq;
 
 	/* Read an interpret database options */
+
 	options = ldb_msg_new(ltdb->cache);
-	if (options == NULL) goto failed;
+	if (options == NULL) goto failed_and_unlock;
 
 	options_dn = ldb_dn_new(options, ldb, LTDB_OPTIONS);
-	if (options_dn == NULL) goto failed;
+	if (options_dn == NULL) goto failed_and_unlock;
 
 	r= ltdb_search_dn1(module, options_dn, options, 0);
 	talloc_free(options_dn);
 	if (r != LDB_SUCCESS && r != LDB_ERR_NO_SUCH_OBJECT) {
-		goto failed;
+		goto failed_and_unlock;
 	}
 	
 	/* set flags if they do exist */
@@ -479,7 +490,7 @@ int ltdb_cache_load(struct ldb_module *module)
 	ltdb_attributes_unload(module);
 
 	if (ltdb_index_load(module, ltdb) == -1) {
-		goto failed;
+		goto failed_and_unlock;
 	}
 
 	/*
@@ -488,7 +499,7 @@ int ltdb_cache_load(struct ldb_module *module)
 	 * partition module.
 	 */
 	if (ltdb_attributes_load(module) == -1) {
-		goto failed;
+		goto failed_and_unlock;
 	}
 
 	ltdb->GUID_index_syntax = NULL;
@@ -503,10 +514,25 @@ int ltdb_cache_load(struct ldb_module *module)
 	}
 
 done:
+	if (have_write_txn) {
+		if (ltdb->kv_ops->finish_write(ltdb) != 0) {
+			goto failed;
+		}
+	} else {
+		ltdb->kv_ops->unlock_read(module);
+	}
+
 	talloc_free(options);
 	talloc_free(baseinfo);
 	return 0;
 
+failed_and_unlock:
+	if (have_write_txn) {
+		ltdb->kv_ops->abort_write(ltdb);
+	} else {
+		ltdb->kv_ops->unlock_read(module);
+	}
+
 failed:
 	talloc_free(options);
 	talloc_free(baseinfo);