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Freeing the source leads to the iochannel being also freed at qio_channel_fd_source_finalize(). Later, io_watch_poll_prepare() tries to create another source with the same iochannel and hits an use after free: =3D=3D8241=3D=3DERROR: AddressSanitizer: heap-use-after-free on address 0x5= 14000000040 READ of size 8 at 0x514000000040 thread T2 #0 0x561c2d272fcd in object_get_class ../qom/object.c:1043:17 #1 0x561c2d338f84 in QIO_CHANNEL_GET_CLASS include/io/channel.h:29:1 #2 0x561c2d33b26f in qio_channel_create_watch ../io/channel.c:388:30 #3 0x561c2d2f0993 in io_watch_poll_prepare ../chardev/char-io.c:65:20 ... 0x514000000040 is located 0 bytes inside of 392-byte region [0x514000000040= ,0x5140000001c8) freed by thread T2 here: #0 0x561c2d2319a5 in free #1 0x7fb2c0926638 in g_free #2 0x561c2d276507 in object_finalize ../qom/object.c:734:9 #3 0x561c2d271d0d in object_unref ../qom/object.c:1231:9 #4 0x561c2d32ef1d in qio_channel_fd_source_finalize ../io/channel-watc= h.c:95:5 #5 0x7fb2c091d124 in g_source_unref_internal ../glib/gmain.c:2298 #6 0x561c2d2f0b6c in io_watch_poll_prepare ../chardev/char-io.c:71:9 ... previously allocated by thread T3 (connect) here: #0 0x561c2d231c69 in malloc #1 0x7fb2c0926518 in g_malloc #2 0x561c2d27246e in object_new_with_type ../qom/object.c:767:15 #3 0x561c2d272530 in object_new ../qom/object.c:789:12 #4 0x561c2d320193 in qio_channel_socket_new ../io/channel-socket.c:64:= 31 #5 0x561c2d308013 in tcp_chr_connect_client_async ../chardev/char-sock= et.c:1181:12 #6 0x561c2d3002e7 in qmp_chardev_open_socket_client ../chardev/char-so= cket.c:1281:9 ... Fix the issue by incrementing the iochannel reference count when the IOWatchPoll takes a reference and decrementing when it is finalized. Signed-off-by: Fabiano Rosas Reviewed-by: Daniel P. Berrang=C3=A9 [PMM: rebased] Signed-off-by: Peter Maydell --- chardev/char-io.c | 5 +++++ 1 file changed, 5 insertions(+) diff --git a/chardev/char-io.c b/chardev/char-io.c index beac5cd245..0e5ba316ed 100644 --- a/chardev/char-io.c +++ b/chardev/char-io.c @@ -88,6 +88,9 @@ static gboolean io_watch_poll_dispatch(GSource *source, G= SourceFunc callback, static void io_watch_poll_finalize(GSource *source) { IOWatchPoll *iwp =3D io_watch_poll_from_source(source); + + object_unref(OBJECT(iwp->ioc)); + if (iwp->src) { g_source_destroy(iwp->src); g_source_unref(iwp->src); @@ -117,6 +120,8 @@ GSource *io_add_watch_poll(Chardev *chr, iwp->fd_can_read =3D fd_can_read; iwp->opaque =3D user_data; iwp->ioc =3D ioc; + object_ref(OBJECT(iwp->ioc)); + iwp->fd_read =3D (GSourceFunc) fd_read; iwp->src =3D NULL; iwp->context =3D context; --=20 2.43.0