clang's sanitizer is picky: memset(NULL, x, 0) is technically
undefined behavior, even though no sane implementation of memset()
deferences the NULL. Caught by the nbd-qemu-allocation iotest.
The alternative to checking before each memset is to instead force an
allocation of 1 element instead of g_new0(type, 0)'s behavior of
returning NULL for a 0-length array.
Reported-by: Peter Maydell
Fixes: 3b1f244c59 (nbd: Allow export of multiple bitmaps for one device)
Signed-off-by: Eric Blake
---
nbd/server.c | 13 +
1 file changed, 9 insertions(+), 4 deletions(-)
diff --git a/nbd/server.c b/nbd/server.c
index 6d03e8a4b436..d9164ee6d0da 100644
--- a/nbd/server.c
+++ b/nbd/server.c
@@ -1,5 +1,5 @@
/*
- * Copyright (C) 2016-2020 Red Hat, Inc.
+ * Copyright (C) 2016-2021 Red Hat, Inc.
* Copyright (C) 2005 Anthony Liguori
*
* Network Block Device Server Side
@@ -879,7 +879,9 @@ static bool nbd_meta_qemu_query(NBDClient *client,
NBDExportMetaContexts *meta,
if (!*query) {
if (client->opt == NBD_OPT_LIST_META_CONTEXT) {
meta->allocation_depth = meta->exp->allocation_depth;
-memset(meta->bitmaps, 1, meta->exp->nr_export_bitmaps);
+if (meta->exp->nr_export_bitmaps) {
+memset(meta->bitmaps, 1, meta->exp->nr_export_bitmaps);
+}
}
trace_nbd_negotiate_meta_query_parse("empty");
return true;
@@ -894,7 +896,8 @@ static bool nbd_meta_qemu_query(NBDClient *client,
NBDExportMetaContexts *meta,
if (nbd_strshift(, "dirty-bitmap:")) {
trace_nbd_negotiate_meta_query_parse("dirty-bitmap:");
if (!*query) {
-if (client->opt == NBD_OPT_LIST_META_CONTEXT) {
+if (client->opt == NBD_OPT_LIST_META_CONTEXT &&
+meta->exp->nr_export_bitmaps) {
memset(meta->bitmaps, 1, meta->exp->nr_export_bitmaps);
}
trace_nbd_negotiate_meta_query_parse("empty");
@@ -1024,7 +1027,9 @@ static int nbd_negotiate_meta_queries(NBDClient *client,
/* enable all known contexts */
meta->base_allocation = true;
meta->allocation_depth = meta->exp->allocation_depth;
-memset(meta->bitmaps, 1, meta->exp->nr_export_bitmaps);
+if (meta->exp->nr_export_bitmaps) {
+memset(meta->bitmaps, 1, meta->exp->nr_export_bitmaps);
+}
} else {
for (i = 0; i < nb_queries; ++i) {
ret = nbd_negotiate_meta_query(client, meta, errp);
--
2.33.1