Re: [Qemu-devel] [PATCH v2 01/16] io: store reference to thread information in the QIOTask struct

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

On Mon, Feb 04, 2019 at 11:40:55AM +0100, Marc-André Lureau wrote:
> Hi
> On Mon, Feb 4, 2019 at 11:38 AM Marc-André Lureau
> <marcandre.lureau@redhat.com> wrote:
> >
> > On Wed, Jan 23, 2019 at 6:27 PM Daniel P. Berrangé <berrange@redhat.com> wrote:
> > >
> > > Currently the struct QIOTaskThreadData is only needed by the worker
> > > thread, but a subsequent patch will need to access it from another
> > > context.
> > >
> > > Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
> >
> > Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
> 
> nack:
> 
> 
> $ tests/test-char
> /char/null: OK
> /char/invalid: OK
> /char/ringbuf: OK
> /char/mux: OK
> /char/stdio: OK
> /char/pipe: OK
> /char/file: OK
> /char/file-fifo: OK
> /char/udp: OK
> /char/serial: OK
> /char/hotswap: OK
> /char/websocket: OK
> /char/socket/basic: OK
> /char/socket/reconnect:
> =================================================================
> ==22150==ERROR: AddressSanitizer: heap-use-after-free on address
> 0x606000004198 at pc 0x5618a22be8d3 bp 0x7fffa43d8a80 sp
> 0x7fffa43d8a70
> READ of size 8 at 0x606000004198 thread T0
>     #0 0x5618a22be8d2 in qio_task_thread_result
> /home/elmarco/src/qemu/io/task.c:91
>     #1 0x7f111f08397a  (/lib64/libglib-2.0.so.0+0x4b97a)
>     #2 0x7f111f08706c in g_main_context_dispatch
> (/lib64/libglib-2.0.so.0+0x4f06c)
>     #3 0x5618a23969b7 in glib_pollfds_poll
> /home/elmarco/src/qemu/util/main-loop.c:215
>     #4 0x5618a23969b7 in os_host_main_loop_wait
> /home/elmarco/src/qemu/util/main-loop.c:238
>     #5 0x5618a23969b7 in main_loop_wait
> /home/elmarco/src/qemu/util/main-loop.c:497
>     #6 0x5618a2299786 in main_loop /home/elmarco/src/qemu/tests/test-char.c:27
>     #7 0x5618a229b651 in char_socket_test_common
> /home/elmarco/src/qemu/tests/test-char.c:355
>     #8 0x7f111f0aefc9  (/lib64/libglib-2.0.so.0+0x76fc9)
>     #9 0x7f111f0aee83  (/lib64/libglib-2.0.so.0+0x76e83)
>     #10 0x7f111f0aee83  (/lib64/libglib-2.0.so.0+0x76e83)
>     #11 0x7f111f0af281 in g_test_run_suite (/lib64/libglib-2.0.so.0+0x77281)
>     #12 0x7f111f0af2a4 in g_test_run (/lib64/libglib-2.0.so.0+0x772a4)
>     #13 0x5618a2293859 in main /home/elmarco/src/qemu/tests/test-char.c:971
>     #14 0x7f111de11412 in __libc_start_main (/lib64/libc.so.6+0x24412)
>     #15 0x5618a2295c1d in _start
> (/home/elmarco/src/qemu/build/tests/test-char+0x23ac1d)
> 
> 0x606000004198 is located 56 bytes inside of 64-byte region
> [0x606000004160,0x6060000041a0)
> freed by thread T0 here:
>     #0 0x7f111f2f0480 in free (/lib64/libasan.so.5+0xef480)
>     #1 0x7f111f08ced1 in g_free (/lib64/libglib-2.0.so.0+0x54ed1)
>     #2 0x5618a243759f  (/home/elmarco/src/qemu/build/tests/test-char+0x3dc59f)
> 
> previously allocated by thread T0 here:
>     #0 0x7f111f2f0a50 in __interceptor_calloc (/lib64/libasan.so.5+0xefa50)
>     #1 0x7f111f08ce1d in g_malloc0 (/lib64/libglib-2.0.so.0+0x54e1d)
> 
> SUMMARY: AddressSanitizer: heap-use-after-free
> /home/elmarco/src/qemu/io/task.c:91 in qio_task_thread_result
> Shadow bytes around the buggy address:

FWIW, valgrind reports the same problem

Needs this change squashed in to fix it

diff --git a/io/task.c b/io/task.c
index d100a754d3..396866b10f 100644
--- a/io/task.c
+++ b/io/task.c
@@ -66,6 +66,18 @@ QIOTask *qio_task_new(Object *source,
 
 static void qio_task_free(QIOTask *task)
 {
+    if (task->thread) {
+        if (task->thread->destroy) {
+            task->thread->destroy(task->thread->opaque);
+        }
+
+        if (task->thread->context) {
+            g_main_context_unref(task->thread->context);
+        }
+
+        g_free(task->thread);
+    }
+
     if (task->destroy) {
         task->destroy(task->opaque);
     }
@@ -88,17 +100,6 @@ static gboolean qio_task_thread_result(gpointer opaque)
     trace_qio_task_thread_result(task);
     qio_task_complete(task);
 
-    if (task->thread->destroy) {
-        task->thread->destroy(task->thread->opaque);
-    }
-
-    if (task->thread->context) {
-        g_main_context_unref(task->thread->context);
-    }
-
-    g_free(task->thread);
-    task->thread = NULL;
-
     return FALSE;
 }



Regards,
Daniel
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