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[Qemu-devel] [PATCH] qemu_opt_foreach: Fix crasher


From: Michal Privoznik
Subject: [Qemu-devel] [PATCH] qemu_opt_foreach: Fix crasher
Date: Tue, 16 Aug 2016 17:17:07 +0200

Program terminated with signal SIGSEGV, Segmentation fault.
#0  0x000055baf6ab4adc in qemu_opt_foreach (opts=0x0, func=0x55baf696b650 
<net_vhost_chardev_opts>, opaque=0x7ffc51368c00, errp=0x7ffc51368e48) at 
util/qemu-option.c:617
617         QTAILQ_FOREACH(opt, &opts->head, next) {
[Current thread is 1 (Thread 0x7f1d4970bb40 (LWP 6603))]
(gdb) bt
#0  0x000055baf6ab4adc in qemu_opt_foreach (opts=0x0, func=0x55baf696b650 
<net_vhost_chardev_opts>, opaque=0x7ffc51368c00, errp=0x7ffc51368e48) at 
util/qemu-option.c:617
#1  0x000055baf696b7da in net_vhost_parse_chardev (opts=0x55baf8ff9260, 
errp=0x7ffc51368e48) at net/vhost-user.c:314
#2  0x000055baf696b985 in net_init_vhost_user (netdev=0x55baf8ff9250, 
name=0x55baf879d270 "hostnet2", peer=0x0, errp=0x7ffc51368e48) at 
net/vhost-user.c:360
#3  0x000055baf6960216 in net_client_init1 (object=0x55baf8ff9250, 
is_netdev=true, errp=0x7ffc51368e48) at net/net.c:1051
#4  0x000055baf6960518 in net_client_init (opts=0x55baf776e7e0, is_netdev=true, 
errp=0x7ffc51368f00) at net/net.c:1108
#5  0x000055baf696083f in netdev_add (opts=0x55baf776e7e0, errp=0x7ffc51368f00) 
at net/net.c:1186
#6  0x000055baf69608c7 in qmp_netdev_add (qdict=0x55baf7afaf60, 
ret=0x7ffc51368f50, errp=0x7ffc51368f48) at net/net.c:1205
#7  0x000055baf6622135 in handle_qmp_command (parser=0x55baf77fb590, 
tokens=0x7f1d24011960) at /path/to/qemu.git/monitor.c:3978
#8  0x000055baf6a9d099 in json_message_process_token (lexer=0x55baf77fb598, 
input=0x55baf75acd20, type=JSON_RCURLY, x=113, y=19) at 
qobject/json-streamer.c:105
#9  0x000055baf6abf7aa in json_lexer_feed_char (lexer=0x55baf77fb598, ch=125 
'}', flush=false) at qobject/json-lexer.c:319
#10 0x000055baf6abf8f2 in json_lexer_feed (lexer=0x55baf77fb598, 
buffer=0x7ffc51369170 "}R\204\367\272U", size=1) at qobject/json-lexer.c:369
#11 0x000055baf6a9d13c in json_message_parser_feed (parser=0x55baf77fb590, 
buffer=0x7ffc51369170 "}R\204\367\272U", size=1) at qobject/json-streamer.c:124
#12 0x000055baf66221f7 in monitor_qmp_read (opaque=0x55baf77fb530, 
buf=0x7ffc51369170 "}R\204\367\272U", size=1) at 
/path/to/qemu.git/monitor.c:3994
#13 0x000055baf6757014 in qemu_chr_be_write_impl (s=0x55baf7610a40, 
buf=0x7ffc51369170 "}R\204\367\272U", len=1) at qemu-char.c:387
#14 0x000055baf6757076 in qemu_chr_be_write (s=0x55baf7610a40, 
buf=0x7ffc51369170 "}R\204\367\272U", len=1) at qemu-char.c:399
#15 0x000055baf675b3b0 in tcp_chr_read (chan=0x55baf90244b0, cond=G_IO_IN, 
opaque=0x55baf7610a40) at qemu-char.c:2927
#16 0x000055baf6a5d655 in qio_channel_fd_source_dispatch 
(source=0x55baf7610df0, callback=0x55baf675b25a <tcp_chr_read>, 
user_data=0x55baf7610a40) at io/channel-watch.c:84
#17 0x00007f1d3e80cbbd in g_main_context_dispatch () from 
/usr/lib64/libglib-2.0.so.0
#18 0x000055baf69d3720 in glib_pollfds_poll () at main-loop.c:213
#19 0x000055baf69d37fd in os_host_main_loop_wait (timeout=126000000) at 
main-loop.c:258
#20 0x000055baf69d38ad in main_loop_wait (nonblocking=0) at main-loop.c:506
#21 0x000055baf676587b in main_loop () at vl.c:1908
#22 0x000055baf676d3bf in main (argc=101, argv=0x7ffc5136a6c8, 
envp=0x7ffc5136a9f8) at vl.c:4604
(gdb) p opts
$1 = (QemuOpts *) 0x0

The crash occurred when I tried to attach vhost-user net:

{"execute":"chardev-add","arguments":{"id":"charnet2","backend":{"type":"socket","data":{"addr":{"type":"unix","data":{"path":"/var/run/openvswitch/vhost-user1"}},"wait":false,"server":false}}},"id":"libvirt-19"}
{"return": {}, "id": "libvirt-19"}
{"execute":"netdev_add","arguments":{"type":"vhost-user","chardev":"charnet2","id":"hostnet2"},"id":"libvirt-20"}

2016-08-16 14:52:18.274+0000: 6456: error : qemuMonitorIORead:586 : Unable to 
read from monitor: Connection reset by peer


The solution is to teach qemu_opt_foreach() to take a shortcut if
@opts is NULL.

Signed-off-by: Michal Privoznik <address@hidden>
---

Even after this patch I'm still unable to attach vhost-user:

{"id": "libvirt-20", "error": {"class": "GenericError", "desc": "chardev 
\"charnet2\" is not a unix socket"}}

But at least, qemu does not crash anymore.

 util/qemu-option.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/util/qemu-option.c b/util/qemu-option.c
index 3467dc2..78be7e1 100644
--- a/util/qemu-option.c
+++ b/util/qemu-option.c
@@ -614,6 +614,11 @@ int qemu_opt_foreach(QemuOpts *opts, qemu_opt_loopfunc 
func, void *opaque,
     QemuOpt *opt;
     int rc;
 
+    if (!opts) {
+        /* Done, trivially. */
+        return 0;
+    }
+
     QTAILQ_FOREACH(opt, &opts->head, next) {
         rc = func(opaque, opt->name, opt->str, errp);
         if (rc) {
-- 
2.8.4




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