Commit 1423c170b9 for qemu.org

commit 1423c170b968b809759848d79a94ec7c6a23269d
Author: Fabiano Rosas <farosas@suse.de>
Date:   Fri Mar 6 09:01:12 2026 +0000

    chardev: Fix QIOChannel refcount

    The IOWatchPoll holds a reference to the iochannel while the "child"
    source (iwp->src) is removed from the context and freed. 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:

    ==8241==ERROR: AddressSanitizer: heap-use-after-free on address 0x514000000040
    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-watch.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-socket.c:1181:12
        #6 0x561c2d3002e7 in qmp_chardev_open_socket_client  ../chardev/char-socket.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 <farosas@suse.de>
    Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
    Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
    Message-id: 20260302092225.4088227-6-peter.maydell@linaro.org
    [PMM: rebased]
    Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

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, GSourceFunc callback,
 static void io_watch_poll_finalize(GSource *source)
 {
     IOWatchPoll *iwp = 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 = fd_can_read;
     iwp->opaque = user_data;
     iwp->ioc = ioc;
+    object_ref(OBJECT(iwp->ioc));
+
     iwp->fd_read = (GSourceFunc) fd_read;
     iwp->src = NULL;
     iwp->context = context;