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);
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-kotov@yandex-team.ru>
Message-Id: <20190408113343.2370-1-yury-kotov@yandex-team.ru>
Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Fixed up comment formatting
fd392cfa8e