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migration: Fix use-after-free of migration state object 

We're currently allowing the process_incoming_migration_bh bottom-half
to run without holding a reference to the 'current_migration' object,
which leads to a segmentation fault if the BH is still live after
migration_shutdown() has dropped the last reference to
current_migration.

In my system the bug manifests as migrate_multifd() returning true
when it shouldn't and multifd_load_shutdown() calling
multifd_recv_terminate_threads() which crashes due to an uninitialized
multifd_recv_state.

Fix the issue by holding a reference to the object when scheduling the
BH and dropping it before returning from the BH. The same is already
done for the cleanup_bh at migrate_fd_cleanup_schedule().

Resolves: https://gitlab.com/qemu-project/qemu/-/issues/1969
Signed-off-by: Fabiano Rosas <farosas@suse.de>
Link: https://lore.kernel.org/r/20240119233922.32588-2-farosas@suse.de
Signed-off-by: Peter Xu <peterx@redhat.com>
(cherry picked from commit 27eb8499ed)
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>
Fabiano Rosas 2024-01-19 20:39:18 -03:00 committed by Michael Tokarev
parent 0c918cb0ab
commit 18c776ecf6
1 changed files with 2 additions and 0 deletions
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2
migration/migration.c
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@ -572,6 +572,7 @@ static void process_incoming_migration_bh(void *opaque)
MIGRATION_STATUS_COMPLETED);
qemu_bh_delete(mis->bh);
migration_incoming_state_destroy();
object_unref(OBJECT(migrate_get_current()));
}
static void coroutine_fn
@ -638,6 +639,7 @@ process_incoming_migration_co(void *opaque)
goto fail;
}
mis->bh = qemu_bh_new(process_incoming_migration_bh, mis);
object_ref(OBJECT(migrate_get_current()));
qemu_bh_schedule(mis->bh);
mis->migration_incoming_co = NULL;
return;