block/monitor: reject persistent bitmap add on a read-only node

qmp_block_dirty_bitmap_add() marks a new bitmap persistent without
checking write access to its node. bdrv_create_dirty_bitmap() always
creates bitmaps writable, so a persistent bitmap added to an
already read-only node stays writable in memory on a node that can
never store it, and the next global inactivation fails:

  Lost persistent bitmaps during inactivation of node '<node>': No write access
  migration_block_inactivate: bdrv_inactivate_all() failed: -22

Forcing it read-only instead does not help: it was never stored,
so it stays unpromotable on the next reopen to read-write and can
trip bdrv_set_dirty()'s readonly assert on the first write. Reject
the add instead, for both read-only and inactive nodes -- an
already-inactive node skips qcow2_inactivate() on close, so a
bitmap added during that window would never get stored either.
Wrapped in a transaction, this denies the whole transaction, since
qmp_transaction() is already all-or-none.

Signed-off-by: Denis V. Lunev <den@openvz.org>
CC: Eric Blake <eblake@redhat.com>
CC: Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru>
CC: John Snow <jsnow@redhat.com>
CC: Andrey Drobyshev <andrey.drobyshev@virtuozzo.com>
Message-ID: <20260716112242.3000035-2-den@openvz.org>
Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru>
Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru>

1 files changed, 11 insertions, 4 deletions

diff --git a/block/monitor/bitmap-qmp-cmds.c b/block/monitor/bitmap-qmp-cmds.c
index a738e7bbf7..d87ca982aa 100644
--- a/block/monitor/bitmap-qmp-cmds.c
+++ b/block/monitor/bitmap-qmp-cmds.c
@@ -125,10 +125,17 @@ void qmp_block_dirty_bitmap_add(const char *node, const char *name,
         disabled = false;
     }
 
-    if (persistent &&
-        !bdrv_can_store_new_dirty_bitmap(bs, name, granularity, errp))
-    {
-        return;
+    if (persistent) {
+        if (!bdrv_is_writable(bs)) {
+            error_setg(errp, "Cannot add a persistent bitmap to "
+                       "read-only or inactive node '%s'",
+                       bdrv_get_node_name(bs));
+            return;
+        }
+
+        if (!bdrv_can_store_new_dirty_bitmap(bs, name, granularity, errp)) {
+            return;
+        }
     }
 
     bitmap = bdrv_create_dirty_bitmap(bs, granularity, name, errp);