Re: [Qemu-devel] [PATCH] vhost-user: don't poke at chardev internal QemuOpts

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

On Fri, Oct 07, 2016 at 09:10:27AM +0000, Marc-André Lureau wrote:
> Hi
> 
> On Fri, Oct 7, 2016 at 1:04 PM Daniel P. Berrange <berrange@redhat.com>
> wrote:
> 
> > The vhost-user code is poking at the QemuOpts instance
> > in the CharDriverState struct, not realizing that it is
> > valid for this to be NULL. e.g. the following crash
> > shows a codepath where it will be NULL:
> >
> >  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 attaching vhost-user net via QMP:
> >
> > {
> >     "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"
> > }
> >
> > The vhost-user code should not be poking at the internals of the
> > CharDriverState struct. What it wants is a chardev that is operating
> > as a network server, so add an explicit API to allow it to validate
> > this feature condition without looking at chardev internals.
> >
> 
> It has to be a unix socket too, why did you drop that check?

Oh does it ?  I was reading the code as allowing a TCP or UNIX
server.  What aspect of it requires UNIX sockets ?


Regards,
Daniel
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