block: bdrv_inactivate_recurse(): check for permissions and fix crash

We must not inactivate child when parent has write permissions on
it.

Calling .bdrv_inactivate() doesn't help: actually only qcow2 has this
handler and it is used to flush caches, not for permission
manipulations.

So, let's simply check cumulative parent permissions before
inactivating the node.

This commit fixes a crash when we do migration during backup: prior to
the commit nothing prevents all nodes inactivation at migration finish
and following backup write to the target crashes on assertion
"assert(!(bs->open_flags & BDRV_O_INACTIVE));" in
bdrv_co_write_req_prepare().

After the commit, we rely on the fact that copy-before-write filter
keeps write permission on target node to be able to write to it. So
inactivation fails and migration fails as expected.

Corresponding test now passes, so, enable it.

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Reviewed-by: Hanna Reitz <hreitz@redhat.com>
Message-Id: <20210911120027.8063-3-vsementsov@virtuozzo.com>
Signed-off-by: Hanna Reitz <hreitz@redhat.com>

diff --git a/block.c b/block.c
index 00982edf45bb3aa8c366847614f0d3f3b385fd79..5ce08a79fda7184d64e2edc05656072f7692a269 100644 (file)
--- a/block.c
+++ b/block.c
@@ -6326,6 +6326,7 @@ static int bdrv_inactivate_recurse(BlockDriverState *bs)
 {
     BdrvChild *child, *parent;
     int ret;
+    uint64_t cumulative_perms, cumulative_shared_perms;
 
     if (!bs->drv) {
         return -ENOMEDIUM;
@@ -6356,6 +6357,13 @@ static int bdrv_inactivate_recurse(BlockDriverState *bs)
         }
     }
 
+    bdrv_get_cumulative_perm(bs, &cumulative_perms,
+                             &cumulative_shared_perms);
+    if (cumulative_perms & (BLK_PERM_WRITE | BLK_PERM_WRITE_UNCHANGED)) {
+        /* Our inactive parents still need write access. Inactivation failed. */
+        return -EPERM;
+    }
+
     bs->open_flags |= BDRV_O_INACTIVE;
 
     /*

diff --git a/tests/qemu-iotests/tests/migrate-during-backup b/tests/qemu-iotests/tests/migrate-during-backup
index 1046904c5a03f78e046f7f7cce3b5eb2713b10a1..34103229eefb3a7d8038c625389716b2b698c924 100755 (executable)
--- a/tests/qemu-iotests/tests/migrate-during-backup
+++ b/tests/qemu-iotests/tests/migrate-during-backup
@@ -1,5 +1,5 @@
 #!/usr/bin/env python3
-# group: migration disabled
+# group: migration
 #
 # Copyright (c) 2021 Virtuozzo International GmbH
 #