* Yury Kotov (yury-ko...@yandex-team.ru) wrote:
> It fixes heap-use-after-free which was found by clang's ASAN.
>
> Control flow of this use-after-free:
> main_thread:
> * Got SIGTERM and completes main loop
> * Calls migration_shutdown
> - migrate_fd_cancel (so, migration_thread begins to complete)
> - object_unref(OBJECT(current_migration));
>
> migration_thread:
> * migration_iteration_finish -> schedule cleanup bh
> * object_unref(OBJECT(s)); (Now, current_migration is freed)
> * exits
>
> main_thread:
> * Calls vm_shutdown -> drain bdrvs -> main loop
> -> cleanup_bh -> use after free
>
> If you want to reproduce, these couple of sleeps will help:
> vl.c:4613:
> migration_shutdown();
> + sleep(2);
> migration.c:3269:
> + sleep(1);
> trace_migration_thread_after_loop();
> migration_iteration_finish(s);
Fun; I hadn't realised you could get more main loop after exiting
the main loop.
Is this fallout from my 892ae715b6b or is this just another case it
didn't catch?
I guess it moved the shutdown early, so it probably is fallout, and
so probably does need to go to 4.0 ?
> Original output:
> qemu-system-x86_64: terminating on signal 15 from pid 31980 (<unknown
> process>)
> =================================================================
> ==31958==ERROR: AddressSanitizer: heap-use-after-free on address
> 0x61900001d210
> at pc 0x555558a535ca bp 0x7fffffffb190 sp 0x7fffffffb188
> READ of size 8 at 0x61900001d210 thread T0 (qemu-vm-0)
> #0 0x555558a535c9 in migrate_fd_cleanup migration/migration.c:1502:23
> #1 0x5555594fde0a in aio_bh_call util/async.c:90:5
> #2 0x5555594fe522 in aio_bh_poll util/async.c:118:13
> #3 0x555559524783 in aio_poll util/aio-posix.c:725:17
> #4 0x555559504fb3 in aio_wait_bh_oneshot util/aio-wait.c:71:5
> #5 0x5555573bddf6 in virtio_blk_data_plane_stop
> hw/block/dataplane/virtio-blk.c:282:5
> #6 0x5555589d5c09 in virtio_bus_stop_ioeventfd
> hw/virtio/virtio-bus.c:246:9
> #7 0x5555589e9917 in virtio_pci_stop_ioeventfd
> hw/virtio/virtio-pci.c:287:5
> #8 0x5555589e22bf in virtio_pci_vmstate_change
> hw/virtio/virtio-pci.c:1072:9
> #9 0x555557628931 in virtio_vmstate_change hw/virtio/virtio.c:2257:9
> #10 0x555557c36713 in vm_state_notify vl.c:1605:9
> #11 0x55555716ef53 in do_vm_stop cpus.c:1074:9
> #12 0x55555716eeff in vm_shutdown cpus.c:1092:12
> #13 0x555557c4283e in main vl.c:4617:5
> #14 0x7fffdfdb482f in __libc_start_main
> (/lib/x86_64-linux-gnu/libc.so.6+0x2082f)
> #15 0x555556ecb118 in _start (x86_64-softmmu/qemu-system-x86_64+0x1977118)
>
> 0x61900001d210 is located 144 bytes inside of 952-byte region
> [0x61900001d180,0x61900001d538)
> freed by thread T6 (live_migration) here:
> #0 0x555556f76782 in __interceptor_free
>
> /tmp/final/llvm.src/projects/compiler-rt/lib/asan/asan_malloc_linux.cc:124:3
> #1 0x555558d5fa94 in object_finalize qom/object.c:618:9
> #2 0x555558d57651 in object_unref qom/object.c:1068:9
> #3 0x555558a55588 in migration_thread migration/migration.c:3272:5
> #4 0x5555595393f2 in qemu_thread_start util/qemu-thread-posix.c:502:9
> #5 0x7fffe057f6b9 in start_thread
> (/lib/x86_64-linux-gnu/libpthread.so.0+0x76b9)
>
> previously allocated by thread T0 (qemu-vm-0) here:
> #0 0x555556f76b03 in __interceptor_malloc
>
> /tmp/final/llvm.src/projects/compiler-rt/lib/asan/asan_malloc_linux.cc:146:3
> #1 0x7ffff6ee37b8 in g_malloc
> (/lib/x86_64-linux-gnu/libglib-2.0.so.0+0x4f7b8)
> #2 0x555558d58031 in object_new qom/object.c:640:12
> #3 0x555558a31f21 in migration_object_init migration/migration.c:139:25
> #4 0x555557c41398 in main vl.c:4320:5
> #5 0x7fffdfdb482f in __libc_start_main
> (/lib/x86_64-linux-gnu/libc.so.6+0x2082f)
>
> Thread T6 (live_migration) created by T0 (qemu-vm-0) here:
> #0 0x555556f5f0dd in pthread_create
>
> /tmp/final/llvm.src/projects/compiler-rt/lib/asan/asan_interceptors.cc:210:3
> #1 0x555559538cf9 in qemu_thread_create util/qemu-thread-posix.c:539:11
> #2 0x555558a53304 in migrate_fd_connect migration/migration.c:3332:5
> #3 0x555558a72bd8 in migration_channel_connect migration/channel.c:92:5
> #4 0x555558a6ef87 in exec_start_outgoing_migration migration/exec.c:42:5
> #5 0x555558a4f3c2 in qmp_migrate migration/migration.c:1922:9
> #6 0x555558bb4f6a in qmp_marshal_migrate
> qapi/qapi-commands-migration.c:607:5
> #7 0x555559363738 in do_qmp_dispatch qapi/qmp-dispatch.c:131:5
> #8 0x555559362a15 in qmp_dispatch qapi/qmp-dispatch.c:174:11
> #9 0x5555571bac15 in monitor_qmp_dispatch monitor.c:4124:11
> #10 0x55555719a22d in monitor_qmp_bh_dispatcher monitor.c:4207:9
> #11 0x5555594fde0a in aio_bh_call util/async.c:90:5
> #12 0x5555594fe522 in aio_bh_poll util/async.c:118:13
> #13 0x5555595201e0 in aio_dispatch util/aio-posix.c:460:5
> #14 0x555559503553 in aio_ctx_dispatch util/async.c:261:5
> #15 0x7ffff6ede196 in g_main_context_dispatch
> (/lib/x86_64-linux-gnu/libglib-2.0.so.0+0x4a196)
>
> SUMMARY: AddressSanitizer: heap-use-after-free migration/migration.c:1502:23
> in migrate_fd_cleanup
> Shadow bytes around the buggy address:
> 0x0c327fffb9f0: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
> 0x0c327fffba00: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
> 0x0c327fffba10: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
> 0x0c327fffba20: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
> 0x0c327fffba30: fd fd fd fd fd fd fd fd fd fd fd fd fd fd fd fd
> =>0x0c327fffba40: fd fd[fd]fd fd fd fd fd fd fd fd fd fd fd fd fd
> 0x0c327fffba50: fd fd fd fd fd fd fd fd fd fd fd fd fd fd fd fd
> 0x0c327fffba60: fd fd fd fd fd fd fd fd fd fd fd fd fd fd fd fd
> 0x0c327fffba70: fd fd fd fd fd fd fd fd fd fd fd fd fd fd fd fd
> 0x0c327fffba80: fd fd fd fd fd fd fd fd fd fd fd fd fd fd fd fd
> 0x0c327fffba90: fd fd fd fd fd fd fd fd fd fd fd fd fd fd fd fd
> Shadow byte legend (one shadow byte represents 8 application bytes):
> Addressable: 00
> Partially addressable: 01 02 03 04 05 06 07
> Heap left redzone: fa
> Freed heap region: fd
> Stack left redzone: f1
> Stack mid redzone: f2
> Stack right redzone: f3
> Stack after return: f5
> Stack use after scope: f8
> Global redzone: f9
> Global init order: f6
> Poisoned by user: f7
> Container overflow: fc
> Array cookie: ac
> Intra object redzone: bb
> ASan internal: fe
> Left alloca redzone: ca
> Right alloca redzone: cb
> Shadow gap: cc
> ==31958==ABORTING
>
> Signed-off-by: Yury Kotov <yury-ko...@yandex-team.ru>
> ---
> migration/migration.c | 30 ++++++++++++++++++++++++------
> 1 file changed, 24 insertions(+), 6 deletions(-)
>
> diff --git a/migration/migration.c b/migration/migration.c
> index 609e0df5d0..54d82bb88b 100644
> --- a/migration/migration.c
> +++ b/migration/migration.c
> @@ -128,6 +128,8 @@ static int migration_maybe_pause(MigrationState *s,
> int *current_active_state,
> int new_state);
> static void migrate_fd_cancel(MigrationState *s);
> +static void migrate_join_thread(MigrationState *s);
> +static void migrate_fd_cleanup(void *opaque);
>
> void migration_object_init(void)
> {
> @@ -176,6 +178,17 @@ void migration_shutdown(void)
> * stop the migration using this structure
> */
> migrate_fd_cancel(current_migration);
> + /*
> + * migration_thread schedules cleanup_bh, but migration_shutdown is
> called
> + * from the end of main, so cleanu_up may not be called because
> main-loop is
> + * complete. So, wait for the complition of migration_thread, cancel bh
> and
> + * call cleanup ourselves.
> + */
(Some typos)
> + migrate_join_thread(current_migration);
I'll admit to being a bit nervous that something in here could be
hanging and thus we could hang here rather than die as SIGTERM is
expecting us to.
> + if (current_migration->cleanup_bh) {
> + qemu_bh_cancel(current_migration->cleanup_bh);
Is that needed? Doesn't migrate_fd_cleanup start with a qemu_bh_delete?
> + migrate_fd_cleanup(current_migration);
> + }
> object_unref(OBJECT(current_migration));
> }
>
> @@ -1495,6 +1508,16 @@ static void block_cleanup_parameters(MigrationState *s)
> }
> }
>
> +static void migrate_join_thread(MigrationState *s)
> +{
> + qemu_mutex_unlock_iothread();
> + if (s->migration_thread_running) {
> + qemu_thread_join(&s->thread);
> + s->migration_thread_running = false;
> + }
> + qemu_mutex_lock_iothread();
> +}
> +
> static void migrate_fd_cleanup(void *opaque)
> {
> MigrationState *s = opaque;
> @@ -1508,12 +1531,7 @@ static void migrate_fd_cleanup(void *opaque)
> QEMUFile *tmp;
>
> trace_migrate_fd_cleanup();
> - qemu_mutex_unlock_iothread();
> - if (s->migration_thread_running) {
> - qemu_thread_join(&s->thread);
> - s->migration_thread_running = false;
> - }
> - qemu_mutex_lock_iothread();
> + migrate_join_thread(s);
>
> multifd_save_cleanup();
> qemu_mutex_lock(&s->qemu_file_lock);
Dave
> --
> 2.21.0
>
--
Dr. David Alan Gilbert / dgilb...@redhat.com / Manchester, UK
