[PULL 06/13] io: fix use after free in websocket handshake code

["Daniel P. Berrangé" <berrange@redhat.com>]

If the QIOChannelWebsock object is freed while it is waiting to
complete a handshake, a GSource is leaked. This can lead to the
callback firing later on and triggering a use-after-free in the
use of the channel. This was observed in the VNC server with the
following trace from valgrind:

==2523108== Invalid read of size 4
==2523108==    at 0x4054A24: vnc_disconnect_start (vnc.c:1296)
==2523108==    by 0x4054A24: vnc_client_error (vnc.c:1392)
==2523108==    by 0x4068A09: vncws_handshake_done (vnc-ws.c:105)
==2523108==    by 0x44863B4: qio_task_complete (task.c:197)
==2523108==    by 0x448343D: qio_channel_websock_handshake_io (channel-websock.c:588)
==2523108==    by 0x6EDB862: UnknownInlinedFun (gmain.c:3398)
==2523108==    by 0x6EDB862: g_main_context_dispatch_unlocked.lto_priv.0 (gmain.c:4249)
==2523108==    by 0x6EDBAE4: g_main_context_dispatch (gmain.c:4237)
==2523108==    by 0x45EC79F: glib_pollfds_poll (main-loop.c:287)
==2523108==    by 0x45EC79F: os_host_main_loop_wait (main-loop.c:310)
==2523108==    by 0x45EC79F: main_loop_wait (main-loop.c:589)
==2523108==    by 0x423A56D: qemu_main_loop (runstate.c:835)
==2523108==    by 0x454F300: qemu_default_main (main.c:37)
==2523108==    by 0x73D6574: (below main) (libc_start_call_main.h:58)
==2523108==  Address 0x57a6e0dc is 28 bytes inside a block of size 103,608 free'd
==2523108==    at 0x5F2FE43: free (vg_replace_malloc.c:989)
==2523108==    by 0x6EDC444: g_free (gmem.c:208)
==2523108==    by 0x4053F23: vnc_update_client (vnc.c:1153)
==2523108==    by 0x4053F23: vnc_refresh (vnc.c:3225)
==2523108==    by 0x4042881: dpy_refresh (console.c:880)
==2523108==    by 0x4042881: gui_update (console.c:90)
==2523108==    by 0x45EFA1B: timerlist_run_timers.part.0 (qemu-timer.c:562)
==2523108==    by 0x45EFC8F: timerlist_run_timers (qemu-timer.c:495)
==2523108==    by 0x45EFC8F: qemu_clock_run_timers (qemu-timer.c:576)
==2523108==    by 0x45EFC8F: qemu_clock_run_all_timers (qemu-timer.c:663)
==2523108==    by 0x45EC765: main_loop_wait (main-loop.c:600)
==2523108==    by 0x423A56D: qemu_main_loop (runstate.c:835)
==2523108==    by 0x454F300: qemu_default_main (main.c:37)
==2523108==    by 0x73D6574: (below main) (libc_start_call_main.h:58)
==2523108==  Block was alloc'd at
==2523108==    at 0x5F343F3: calloc (vg_replace_malloc.c:1675)
==2523108==    by 0x6EE2F81: g_malloc0 (gmem.c:133)
==2523108==    by 0x4057DA3: vnc_connect (vnc.c:3245)
==2523108==    by 0x448591B: qio_net_listener_channel_func (net-listener.c:54)
==2523108==    by 0x6EDB862: UnknownInlinedFun (gmain.c:3398)
==2523108==    by 0x6EDB862: g_main_context_dispatch_unlocked.lto_priv.0 (gmain.c:4249)
==2523108==    by 0x6EDBAE4: g_main_context_dispatch (gmain.c:4237)
==2523108==    by 0x45EC79F: glib_pollfds_poll (main-loop.c:287)
==2523108==    by 0x45EC79F: os_host_main_loop_wait (main-loop.c:310)
==2523108==    by 0x45EC79F: main_loop_wait (main-loop.c:589)
==2523108==    by 0x423A56D: qemu_main_loop (runstate.c:835)
==2523108==    by 0x454F300: qemu_default_main (main.c:37)
==2523108==    by 0x73D6574: (below main) (libc_start_call_main.h:58)
==2523108==

The above can be reproduced by launching QEMU with

  $ qemu-system-x86_64 -vnc localhost:0,websocket=5700

and then repeatedly running:

  for i in {1..100}; do
     (echo -n "GET / HTTP/1.1" && sleep 0.05) | nc -w 1 localhost 5700 &
  done

CVE-2025-11234
Reported-by: Grant Millar | Cylo <rid@cylo.io>
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
---
 include/io/channel-websock.h |  3 ++-
 io/channel-websock.c         | 22 ++++++++++++++++------
 2 files changed, 18 insertions(+), 7 deletions(-)

diff --git a/include/io/channel-websock.h b/include/io/channel-websock.h
index e180827c57..6700cf8946 100644
--- a/include/io/channel-websock.h
+++ b/include/io/channel-websock.h
@@ -61,7 +61,8 @@ struct QIOChannelWebsock {
     size_t payload_remain;
     size_t pong_remain;
     QIOChannelWebsockMask mask;
-    guint io_tag;
+    guint hs_io_tag; /* tracking handshake task */
+    guint io_tag; /* tracking watch task */
     Error *io_err;
     gboolean io_eof;
     uint8_t opcode;
diff --git a/io/channel-websock.c b/io/channel-websock.c
index a50a160e18..cb4dafdebb 100644
--- a/io/channel-websock.c
+++ b/io/channel-websock.c
@@ -545,6 +545,7 @@ static gboolean qio_channel_websock_handshake_send(QIOChannel *ioc,
         trace_qio_channel_websock_handshake_fail(ioc, error_get_pretty(err));
         qio_task_set_error(task, err);
         qio_task_complete(task);
+        wioc->hs_io_tag = 0;
         return FALSE;
     }
 
@@ -560,6 +561,7 @@ static gboolean qio_channel_websock_handshake_send(QIOChannel *ioc,
             trace_qio_channel_websock_handshake_complete(ioc);
             qio_task_complete(task);
         }
+        wioc->hs_io_tag = 0;
         return FALSE;
     }
     trace_qio_channel_websock_handshake_pending(ioc, G_IO_OUT);
@@ -586,6 +588,7 @@ static gboolean qio_channel_websock_handshake_io(QIOChannel *ioc,
         trace_qio_channel_websock_handshake_fail(ioc, error_get_pretty(err));
         qio_task_set_error(task, err);
         qio_task_complete(task);
+        wioc->hs_io_tag = 0;
         return FALSE;
     }
     if (ret == 0) {
@@ -597,7 +600,7 @@ static gboolean qio_channel_websock_handshake_io(QIOChannel *ioc,
     error_propagate(&wioc->io_err, err);
 
     trace_qio_channel_websock_handshake_reply(ioc);
-    qio_channel_add_watch(
+    wioc->hs_io_tag = qio_channel_add_watch(
         wioc->master,
         G_IO_OUT,
         qio_channel_websock_handshake_send,
@@ -907,11 +910,12 @@ void qio_channel_websock_handshake(QIOChannelWebsock *ioc,
 
     trace_qio_channel_websock_handshake_start(ioc);
     trace_qio_channel_websock_handshake_pending(ioc, G_IO_IN);
-    qio_channel_add_watch(ioc->master,
-                          G_IO_IN,
-                          qio_channel_websock_handshake_io,
-                          task,
-                          NULL);
+    ioc->hs_io_tag = qio_channel_add_watch(
+        ioc->master,
+        G_IO_IN,
+        qio_channel_websock_handshake_io,
+        task,
+        NULL);
 }
 
 
@@ -922,6 +926,9 @@ static void qio_channel_websock_finalize(Object *obj)
     buffer_free(&ioc->encinput);
     buffer_free(&ioc->encoutput);
     buffer_free(&ioc->rawinput);
+    if (ioc->hs_io_tag) {
+        g_source_remove(ioc->hs_io_tag);
+    }
     if (ioc->io_tag) {
         g_source_remove(ioc->io_tag);
     }
@@ -1221,6 +1228,9 @@ static int qio_channel_websock_close(QIOChannel *ioc,
     buffer_free(&wioc->encinput);
     buffer_free(&wioc->encoutput);
     buffer_free(&wioc->rawinput);
+    if (wioc->hs_io_tag) {
+        g_clear_handle_id(&wioc->hs_io_tag, g_source_remove);
+    }
     if (wioc->io_tag) {
         g_clear_handle_id(&wioc->io_tag, g_source_remove);
     }
-- 
2.50.1