From baae39c2c63098031cd7448b1b1331bcf6140c45 Mon Sep 17 00:00:00 2001
From: Stefan Hajnoczi <stefanha@redhat.com>
Date: Mon, 12 Jun 2017 14:36:56 +0200
Subject: [PATCH 10/13] virtio-serial: fix segfault on disconnect
RH-Author: Stefan Hajnoczi <stefanha@redhat.com>
Message-id: <20170612143656.19554-2-stefanha@redhat.com>
Patchwork-id: 75591
O-Subject: [RHV-7.4 qemu-kvm-rhev PATCH 1/1] virtio-serial: fix segfault on disconnect
Bugzilla: 1447257
RH-Acked-by: Ladi Prosek <lprosek@redhat.com>
RH-Acked-by: Michael S. Tsirkin <mst@redhat.com>
RH-Acked-by: Pankaj Gupta <pagupta@redhat.com>
Since commit d4c19cdeeb2f1e474bc426a6da261f1d7346eb5b ("virtio-serial:
add missing virtio_detach_element() call") the following commands may
cause QEMU to segfault:
$ qemu -M accel=kvm -cpu host -m 1G \
-drive if=virtio,file=test.img,format=raw \
-device virtio-serial-pci,id=virtio-serial0 \
-chardev socket,id=channel1,path=/tmp/chardev.sock,server,nowait \
-device virtserialport,chardev=channel1,bus=virtio-serial0.0,id=port1
$ nc -U /tmp/chardev.sock
^C
(guest)$ cat /dev/zero >/dev/vport0p1
The segfault is non-deterministic: if the event loop notices the socket
has been closed then there is no crash. The disconnect has to happen
right before QEMU attempts to write data to the socket.
The backtrace is as follows:
Thread 1 "qemu-system-x86" received signal SIGSEGV, Segmentation fault.
0x00005555557e0698 in do_flush_queued_data (port=0x5555582cedf0, vq=0x7fffcc854290, vdev=0x55555807b1d0) at hw/char/virtio-serial-bus.c:180
180 for (i = port->iov_idx; i < port->elem->out_num; i++) {
#1 0x000055555580d363 in virtio_queue_notify_vq (vq=0x7fffcc854290) at hw/virtio/virtio.c:1524
#2 0x000055555580d363 in virtio_queue_host_notifier_read (n=0x7fffcc8542f8) at hw/virtio/virtio.c:2430
#3 0x0000555555b3482c in aio_dispatch_handlers (ctx=ctx@entry=0x5555566b8c80) at util/aio-posix.c:399
#4 0x0000555555b350d8 in aio_dispatch (ctx=0x5555566b8c80) at util/aio-posix.c:430
#5 0x0000555555b3212e in aio_ctx_dispatch (source=<optimized out>, callback=<optimized out>, user_data=<optimized out>) at util/async.c:261
#6 0x00007fffde71de52 in g_main_context_dispatch () at /lib64/libglib-2.0.so.0
#7 0x0000555555b34353 in glib_pollfds_poll () at util/main-loop.c:213
#8 0x0000555555b34353 in os_host_main_loop_wait (timeout=<optimized out>) at util/main-loop.c:261
#9 0x0000555555b34353 in main_loop_wait (nonblocking=<optimized out>) at util/main-loop.c:517
#10 0x0000555555773207 in main_loop () at vl.c:1917
#11 0x0000555555773207 in main (argc=<optimized out>, argv=<optimized out>, envp=<optimized out>) at vl.c:4751
The do_flush_queued_data() function does not anticipate chardev close
events during vsc->have_data(). It expects port->elem to remain
non-NULL for the duration its for loop.
The fix is simply to return from do_flush_queued_data() if the port
closes because the close event already frees port->elem and drains the
virtqueue - there is nothing left for do_flush_queued_data() to do.
Reported-by: Sitong Liu <siliu@redhat.com>
Reported-by: Min Deng <mdeng@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
(cherry picked from commit 46764fe09ca2e0f15c0981a672c166ed8cf57e72)
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Miroslav Rezanina <mrezanin@redhat.com>
---
hw/char/virtio-serial-bus.c | 3 +++
1 file changed, 3 insertions(+)
diff --git a/hw/char/virtio-serial-bus.c b/hw/char/virtio-serial-bus.c
index aa9c11a..f5bc173 100644
--- a/hw/char/virtio-serial-bus.c
+++ b/hw/char/virtio-serial-bus.c
@@ -186,6 +186,9 @@ static void do_flush_queued_data(VirtIOSerialPort *port, VirtQueue *vq,
port->elem->out_sg[i].iov_base
+ port->iov_offset,
buf_size);
+ if (!port->elem) { /* bail if we got disconnected */
+ return;
+ }
if (port->throttled) {
port->iov_idx = i;
if (ret > 0) {
--
1.8.3.1