Re: [Qemu-devel] [PATCH v3] net: don't poke at chardev internal QemuOpts

[Marc-André Lureau]

Hi

On Fri, Oct 7, 2016 at 4:18 PM Daniel P. Berrange <address@hidden>
wrote:

> The vhost-user & colo 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"
> }
>
> Code using chardevs should not be poking at the internals of the
> CharDriverState struct. What vhost-user wants is a chardev that is
> operating as reconnectable network service, along with the ability
> to do FD passing over the connection. The colo code simply wants
> a network service. Add a feature concept to the char drivers so
> that chardev users can query the actual features they wish to have
> supported. The QemuOpts member is removed to prevent future mistakes
> in this area.
>
> Signed-off-by: Daniel P. Berrange <address@hidden>
> ---
>
> Changed in v3:
>
>  - Fix colo code too
>  - Remove QemuOpts from CharDriverState
>  - Generalize to allow both client & server mode chardevs
>    for vhost-user
>
> Changed in v2:
>
>  - Switch to use a bitmap to track features in chardev
>  - Check for FD passing support in chardev
>
>  hmp.c                 |  1 +
>  include/sysemu/char.h | 21 ++++++++++++++++++++-
>  net/colo-compare.c    | 30 ++----------------------------
>  net/vhost-user.c      | 41 +++++++----------------------------------
>  qemu-char.c           | 22 +++++++++++++++++++---
>  5 files changed, 49 insertions(+), 66 deletions(-)
>
> diff --git a/hmp.c b/hmp.c
> index 336e7bf..3c42182 100644
> --- a/hmp.c
> +++ b/hmp.c
> @@ -1909,6 +1909,7 @@ void hmp_chardev_add(Monitor *mon, const QDict
> *qdict)
>          error_setg(&err, "Parsing chardev args failed");
>      } else {
>          qemu_chr_new_from_opts(opts, NULL, &err);
> +        qemu_opts_del(opts);
>

The function no longer takes ownership of opts. Important enough to mention
in commit log perhaps. I guess it's okay to keep opts around after vl.c
chardev_init_func


>      }
>      hmp_handle_error(mon, &err);
>  }
> diff --git a/include/sysemu/char.h b/include/sysemu/char.h
> index 0d0465a..19dad3f 100644
> --- a/include/sysemu/char.h
> +++ b/include/sysemu/char.h
> @@ -9,6 +9,7 @@
>  #include "qapi/qmp/qobject.h"
>  #include "qapi/qmp/qstring.h"
>  #include "qemu/main-loop.h"
> +#include "qemu/bitmap.h"
>
>  /* character device */
>
> @@ -58,6 +59,20 @@ struct ParallelIOArg {
>
>  typedef void IOEventHandler(void *opaque, int event);
>
> +typedef enum {
> +    /* Whether the chardev peer is able to close and
> +     * reopen the data channel, thus requiring support
> +     * for qemu_chr_wait_connected() to wait for a
> +     * valid connection */
> +    QEMU_CHAR_FEATURE_RECONNECTABLE,
> +    /* Whether it is possible to send/recv file descriptors
> +     * over the data channel */
> +    QEMU_CHAR_FEATURE_FD_PASS,
> +
> +    QEMU_CHAR_FEATURE_LAST,
> +} CharDriverFeature;
> +
> +
>  struct CharDriverState {
>      QemuMutex chr_write_lock;
>      void (*init)(struct CharDriverState *s);
> @@ -93,8 +108,8 @@ struct CharDriverState {
>      int avail_connections;
>      int is_mux;
>      guint fd_in_tag;
> -    QemuOpts *opts;
>      bool replay;
> +    DECLARE_BITMAP(features, QEMU_CHAR_FEATURE_LAST);
>      QTAILQ_ENTRY(CharDriverState) next;
>  };
>
> @@ -437,6 +452,10 @@ 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_has_feature(CharDriverState *chr,
> +                          CharDriverFeature feature);
> +void qemu_chr_set_feature(CharDriverState *chr,
> +                          CharDriverFeature feature);
>  QemuOpts *qemu_chr_parse_compat(const char *label, const char *filename);
>
>  void register_char_driver(const char *name, ChardevBackendKind kind,
> diff --git a/net/colo-compare.c b/net/colo-compare.c
> index 22b1da1..47703c5 100644
> --- a/net/colo-compare.c
> +++ b/net/colo-compare.c
> @@ -564,29 +564,6 @@ static void compare_sec_rs_finalize(SocketReadState
> *sec_rs)
>      }
>  }
>
> -static int compare_chardev_opts(void *opaque,
> -                                const char *name, const char *value,
> -                                Error **errp)
> -{
> -    CompareChardevProps *props = opaque;
> -
> -    if (strcmp(name, "backend") == 0 &&
> -        strcmp(value, "socket") == 0) {
> -        props->is_socket = true;
> -        return 0;
> -    } else if (strcmp(name, "host") == 0 ||
> -              (strcmp(name, "port") == 0) ||
> -              (strcmp(name, "server") == 0) ||
> -              (strcmp(name, "wait") == 0) ||
> -              (strcmp(name, "path") == 0)) {
> -        return 0;
> -    } else {
> -        error_setg(errp,
> -                   "COLO-compare does not support a chardev with option
> %s=%s",
> -                   name, value);
> -        return -1;
> -    }
> -}
>
>  /*
>   * Return 0 is success.
> @@ -606,12 +583,9 @@ static int find_and_check_chardev(CharDriverState
> **chr,
>      }
>
>      memset(&props, 0, sizeof(props));
> -    if (qemu_opt_foreach((*chr)->opts, compare_chardev_opts, &props,
> errp)) {
> -        return 1;
> -    }
>
> -    if (!props.is_socket) {
> -        error_setg(errp, "chardev \"%s\" is not a tcp socket",
> +    if (!qemu_chr_has_feature(*chr, QEMU_CHAR_FEATURE_RECONNECTABLE)) {
> +        error_setg(errp, "chardev \"%s\" is not reconnectable",
>                     chr_name);
>          return 1;
>      }
> diff --git a/net/vhost-user.c b/net/vhost-user.c
> index b0595f8..5b94c84 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 +273,23 @@ 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)) {
> +    if (!qemu_chr_has_feature(chr, QEMU_CHAR_FEATURE_RECONNECTABLE)) {
> +        error_setg(errp, "chardev \"%s\" is not reconnectable",
> +                   opts->chardev);
>          return NULL;
>      }
> -
> -    if (!props.is_socket || !props.is_unix) {
> -        error_setg(errp, "chardev \"%s\" is not a unix socket",
> +    if (!qemu_chr_has_feature(chr, QEMU_CHAR_FEATURE_FD_PASS)) {
> +        error_setg(errp, "chardev \"%s\" does not support FD passing",
>                     opts->chardev);
>          return NULL;
>      }
> @@ -357,7 +330,7 @@ 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..768150d 100644
> --- a/qemu-char.c
> +++ b/qemu-char.c
> @@ -3996,7 +3996,6 @@ CharDriverState *qemu_chr_new_from_opts(QemuOpts
> *opts,
>      }
>
>      chr = qemu_chr_find(id);
> -    chr->opts = opts;
>
>  qapi_out:
>      qapi_free_ChardevBackend(backend);
> @@ -4005,7 +4004,6 @@ qapi_out:
>      return chr;
>
>  err:
> -    qemu_opts_del(opts);
>      return NULL;
>  }
>
> @@ -4033,6 +4031,7 @@ CharDriverState *qemu_chr_new_noreplay(const char
> *label, const char *filename,
>          qemu_chr_fe_claim_no_fail(chr);
>          monitor_init(chr, MONITOR_USE_READLINE);
>      }
> +    qemu_opts_del(opts);
>      return chr;
>  }
>
> @@ -4132,7 +4131,6 @@ static void qemu_chr_free_common(CharDriverState
> *chr)
>  {
>      g_free(chr->filename);
>      g_free(chr->label);
> -    qemu_opts_del(chr->opts);
>      if (chr->logfd != -1) {
>          close(chr->logfd);
>      }
> @@ -4513,6 +4511,11 @@ static CharDriverState
> *qmp_chardev_open_socket(const char *id,
>
>      s->addr = QAPI_CLONE(SocketAddress, sock->addr);
>
> +    qemu_chr_set_feature(chr, QEMU_CHAR_FEATURE_RECONNECTABLE);
> +    if (s->is_unix) {
> +        qemu_chr_set_feature(chr, QEMU_CHAR_FEATURE_FD_PASS);
> +    }
> +
>      chr->opaque = s;
>      chr->chr_wait_connected = tcp_chr_wait_connected;
>      chr->chr_write = tcp_chr_write;
> @@ -4596,6 +4599,19 @@ static CharDriverState *qmp_chardev_open_udp(const
> char *id,
>      return qemu_chr_open_udp(sioc, common, errp);
>  }
>
> +
> +bool qemu_chr_has_feature(CharDriverState *chr,
> +                          CharDriverFeature feature)
> +{
> +    return test_bit(feature, chr->features);
> +}
> +
> +void qemu_chr_set_feature(CharDriverState *chr,
> +                           CharDriverFeature feature)
> +{
> +    return set_bit(feature, chr->features);
> +}
> +
>  ChardevReturn *qmp_chardev_add(const char *id, ChardevBackend *backend,
>                                 Error **errp)
>  {
> --
> 2.7.4
>


Reviewed-by: Marc-André Lureau <address@hidden>


-- 
Marc-André Lureau