From ddde5ee769fcc84b96f879d7b94f35268f69ca3b Mon Sep 17 00:00:00 2001 From: Roman Kagan Date: Fri, 29 Jan 2021 10:38:58 +0300 Subject: [PATCH] block/nbd: only enter connection coroutine if it's present When an NBD block driver state is moved from one aio_context to another (e.g. when doing a drain in a migration thread), nbd_client_attach_aio_context_bh is executed that enters the connection coroutine. However, the assumption that ->connection_co is always present here appears incorrect: the connection may have encountered an error other than -EIO in the underlying transport, and thus may have decided to quit rather than keep trying to reconnect, and therefore it may have terminated the connection coroutine. As a result an attempt to reassign the client in this state (NBD_CLIENT_QUIT) to a different aio_context leads to a null pointer dereference: #0 qio_channel_detach_aio_context (ioc=0x0) at /build/qemu-gYtjVn/qemu-5.0.1/io/channel.c:452 #1 0x0000562a242824b3 in bdrv_detach_aio_context (bs=0x562a268d6a00) at /build/qemu-gYtjVn/qemu-5.0.1/block.c:6151 #2 bdrv_set_aio_context_ignore (bs=bs@entry=0x562a268d6a00, new_context=new_context@entry=0x562a260c9580, ignore=ignore@entry=0x7feeadc9b780) at /build/qemu-gYtjVn/qemu-5.0.1/block.c:6230 #3 0x0000562a24282969 in bdrv_child_try_set_aio_context (bs=bs@entry=0x562a268d6a00, ctx=0x562a260c9580, ignore_child=, errp=) at /build/qemu-gYtjVn/qemu-5.0.1/block.c:6332 #4 0x0000562a242bb7db in blk_do_set_aio_context (blk=0x562a2735d0d0, new_context=0x562a260c9580, update_root_node=update_root_node@entry=true, errp=errp@entry=0x0) at /build/qemu-gYtjVn/qemu-5.0.1/block/block-backend.c:1989 #5 0x0000562a242be0bd in blk_set_aio_context (blk=, new_context=, errp=errp@entry=0x0) at /build/qemu-gYtjVn/qemu-5.0.1/block/block-backend.c:2010 #6 0x0000562a23fbd953 in virtio_blk_data_plane_stop (vdev=) at /build/qemu-gYtjVn/qemu-5.0.1/hw/block/dataplane/virtio-blk.c:292 #7 0x0000562a241fc7bf in virtio_bus_stop_ioeventfd (bus=0x562a260dbf08) at /build/qemu-gYtjVn/qemu-5.0.1/hw/virtio/virtio-bus.c:245 #8 0x0000562a23fefb2e in virtio_vmstate_change (opaque=0x562a260dbf90, running=0, state=) at /build/qemu-gYtjVn/qemu-5.0.1/hw/virtio/virtio.c:3220 #9 0x0000562a2402ebfd in vm_state_notify (running=running@entry=0, state=state@entry=RUN_STATE_FINISH_MIGRATE) at /build/qemu-gYtjVn/qemu-5.0.1/softmmu/vl.c:1275 #10 0x0000562a23f7bc02 in do_vm_stop (state=RUN_STATE_FINISH_MIGRATE, send_stop=) at /build/qemu-gYtjVn/qemu-5.0.1/cpus.c:1032 #11 0x0000562a24209765 in migration_completion (s=0x562a260e83a0) at /build/qemu-gYtjVn/qemu-5.0.1/migration/migration.c:2914 #12 migration_iteration_run (s=0x562a260e83a0) at /build/qemu-gYtjVn/qemu-5.0.1/migration/migration.c:3275 #13 migration_thread (opaque=opaque@entry=0x562a260e83a0) at /build/qemu-gYtjVn/qemu-5.0.1/migration/migration.c:3439 #14 0x0000562a2435ca96 in qemu_thread_start (args=) at /build/qemu-gYtjVn/qemu-5.0.1/util/qemu-thread-posix.c:519 #15 0x00007feed31466ba in start_thread (arg=0x7feeadc9c700) at pthread_create.c:333 #16 0x00007feed2e7c41d in __GI___sysctl (name=0x0, nlen=608471908, oldval=0x562a2452b138, oldlenp=0x0, newval=0x562a2452c5e0 <__func__.28102>, newlen=0) at ../sysdeps/unix/sysv/linux/sysctl.c:30 #17 0x0000000000000000 in ?? () Fix it by checking that the connection coroutine is non-null before trying to enter it. If it is null, no entering is needed, as the connection is probably going down anyway. Signed-off-by: Roman Kagan Reviewed-by: Vladimir Sementsov-Ogievskiy Message-Id: <20210129073859.683063-3-rvkagan@yandex-team.ru> Signed-off-by: Eric Blake --- block/nbd.c | 16 +++++++++------- 1 file changed, 9 insertions(+), 7 deletions(-) diff --git a/block/nbd.c b/block/nbd.c index bcd6641e90f5..b3cbbeb4b0cb 100644 --- a/block/nbd.c +++ b/block/nbd.c @@ -250,13 +250,15 @@ static void nbd_client_attach_aio_context_bh(void *opaque) BlockDriverState *bs = opaque; BDRVNBDState *s = (BDRVNBDState *)bs->opaque; - /* - * The node is still drained, so we know the coroutine has yielded in - * nbd_read_eof(), the only place where bs->in_flight can reach 0, or it is - * entered for the first time. Both places are safe for entering the - * coroutine. - */ - qemu_aio_coroutine_enter(bs->aio_context, s->connection_co); + if (s->connection_co) { + /* + * The node is still drained, so we know the coroutine has yielded in + * nbd_read_eof(), the only place where bs->in_flight can reach 0, or + * it is entered for the first time. Both places are safe for entering + * the coroutine. + */ + qemu_aio_coroutine_enter(bs->aio_context, s->connection_co); + } bdrv_dec_in_flight(bs); }