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

[Marc-André Lureau]

Hi

On Fri, Oct 7, 2016 at 1:04 PM Daniel P. Berrange <address@hidden>
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?


>
> Signed-off-by: Daniel P. Berrange <address@hidden>
> ---
>
> NB, I've not functionally tested this - just compiled and
> unit tested.
>
>  include/sysemu/char.h |  1 +
>  net/vhost-user.c      | 40 ++++------------------------------------
>  qemu-char.c           |  7 +++++++
>  3 files changed, 12 insertions(+), 36 deletions(-)
>
> diff --git a/include/sysemu/char.h b/include/sysemu/char.h
> index 0d0465a..50a6603 100644
> --- a/include/sysemu/char.h
> +++ b/include/sysemu/char.h
> @@ -437,6 +437,7 @@ int qemu_chr_add_client(CharDriverState *s, int fd);
>  CharDriverState *qemu_chr_find(const char *name);
>  bool chr_is_ringbuf(const CharDriverState *chr);
>
> +bool qemu_chr_is_network_server(CharDriverState *chr);
>  QemuOpts *qemu_chr_parse_compat(const char *label, const char *filename);
>
>  void register_char_driver(const char *name, ChardevBackendKind kind,
> diff --git a/net/vhost-user.c b/net/vhost-user.c
> index b0595f8..2e2cf24 100644
> --- a/net/vhost-user.c
> +++ b/net/vhost-user.c
> @@ -27,11 +27,6 @@ typedef struct VhostUserState {
>      bool started;
>  } VhostUserState;
>
> -typedef struct VhostUserChardevProps {
> -    bool is_socket;
> -    bool is_unix;
> -} VhostUserChardevProps;
> -
>  VHostNetState *vhost_user_get_vhost_net(NetClientState *nc)
>  {
>      VhostUserState *s = DO_UPCAST(VhostUserState, nc, nc);
> @@ -278,45 +273,18 @@ static int net_vhost_user_init(NetClientState *peer,
> const char *device,
>      return 0;
>  }
>
> -static int net_vhost_chardev_opts(void *opaque,
> -                                  const char *name, const char *value,
> -                                  Error **errp)
> -{
> -    VhostUserChardevProps *props = opaque;
> -
> -    if (strcmp(name, "backend") == 0 && strcmp(value, "socket") == 0) {
> -        props->is_socket = true;
> -    } else if (strcmp(name, "path") == 0) {
> -        props->is_unix = true;
> -    } else if (strcmp(name, "server") == 0) {
> -    } else {
> -        error_setg(errp,
> -                   "vhost-user does not support a chardev with option
> %s=%s",
> -                   name, value);
> -        return -1;
> -    }
> -    return 0;
> -}
> -
> -static CharDriverState *net_vhost_parse_chardev(
> +static CharDriverState *net_vhost_claim_chardev(
>      const NetdevVhostUserOptions *opts, Error **errp)
>  {
>      CharDriverState *chr = qemu_chr_find(opts->chardev);
> -    VhostUserChardevProps props;
>
>      if (chr == NULL) {
>          error_setg(errp, "chardev \"%s\" not found", opts->chardev);
>          return NULL;
>      }
>
> -    /* inspect chardev opts */
> -    memset(&props, 0, sizeof(props));
> -    if (qemu_opt_foreach(chr->opts, net_vhost_chardev_opts, &props,
> errp)) {
> -        return NULL;
> -    }
> -
> -    if (!props.is_socket || !props.is_unix) {
> -        error_setg(errp, "chardev \"%s\" is not a unix socket",
> +    if (!qemu_chr_is_network_server(chr)) {
> +        error_setg(errp, "chardev \"%s\" does not provide a network
> server",
>                     opts->chardev);
>          return NULL;
>      }
> @@ -357,7 +325,7 @@ int net_init_vhost_user(const Netdev *netdev, const
> char *name,
>      assert(netdev->type == NET_CLIENT_DRIVER_VHOST_USER);
>      vhost_user_opts = &netdev->u.vhost_user;
>
> -    chr = net_vhost_parse_chardev(vhost_user_opts, errp);
> +    chr = net_vhost_claim_chardev(vhost_user_opts, errp);
>      if (!chr) {
>          return -1;
>      }
> diff --git a/qemu-char.c b/qemu-char.c
> index fb456ce..977fb1a 100644
> --- a/qemu-char.c
> +++ b/qemu-char.c
> @@ -4596,6 +4596,13 @@ static CharDriverState *qmp_chardev_open_udp(const
> char *id,
>      return qemu_chr_open_udp(sioc, common, errp);
>  }
>
> +
> +bool qemu_chr_is_network_server(CharDriverState *chr)
> +{
> +    return chr->chr_wait_connected != NULL;
> +}
> +
> +
>  ChardevReturn *qmp_chardev_add(const char *id, ChardevBackend *backend,
>                                 Error **errp)
>  {
> --
> 2.7.4
>
> --
Marc-André Lureau