s3:registry: eliminate race condition in creating/scanning sorted subkeys

Called, from key_exists, scan_sorted_subkeys re-creates the sorted
subkeys record of the given key and then searches through it.
The race is that between creation and parsing of the sorted subkey
record, another process that stores some other subkey of the same
parent key will delete the sorted subkey record, resulting in an
WERR_BADFILE of an operation that should actually succeed.

This patch fixes the issue by wrapping the creation and parsing
into a transaction.

Michael
(cherry picked from commit a752bbd10d661ebc93b8d51bd583eb62eb00ad18)

Fix bug #7314 (registry: creation of sorted subkey record is racy (not atomic)).
(cherry picked from commit 06d1aeb7b686b8b929cf9bff48aedc9dbb88b7c3)

diff --git a/source3/registry/reg_backend_db.c b/source3/registry/reg_backend_db.c
index 43963db3c29a26d451b73141f56f73157fd655b6..fe15b4e46185c845be7c0f07e7ef595194384db9 100644 (file)
--- a/source3/registry/reg_backend_db.c
+++ b/source3/registry/reg_backend_db.c
@@ -1368,14 +1368,31 @@ static bool scan_parent_subkeys(struct db_context *db, const char *parent,
        if (state.scanned) {
                result = state.found;
        } else {
+               res = db->transaction_start(db);
+               if (res != 0) {
+                       DEBUG(0, ("error starting transacion\n"));
+                       goto fail;
+               }
+
                if (!create_sorted_subkeys(path, key)) {
+                       res = db->transaction_cancel(db);
+                       if (res != 0) {
+                               smb_panic("Failed to cancel transaction.");
+                       }
                        goto fail;
                }
+
                res = db->parse_record(db, string_term_tdb_data(key),
                                       parent_subkey_scanner, &state);
                if ((res == 0) && (state.scanned)) {
                        result = state.found;
                }
+
+               res = db->transaction_commit(db);
+               if (res != 0) {
+                       DEBUG(0, ("error committing transaction\n"));
+                       result = false;
+               }
        }
 
  fail: