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net: don't poke at chardev internal QemuOpts
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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 <berrange@redhat.com>
Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
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@berrange @mstsirkin
berrange authored and mstsirkin committed Oct 9, 2016
1 parent ad14a46 commit 0a73336
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Showing 5 changed files with 49 additions and 66 deletions.
1 change: 1 addition & 0 deletions hmp.c
View file
Expand Up @@ -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);
}
hmp_handle_error(mon, &err);
}
Expand Down
21 changes: 20 additions & 1 deletion include/sysemu/char.h
View file
Expand Up @@ -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 */

Expand Down Expand Up @@ -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);
Expand Down Expand Up @@ -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;
};

Expand Down Expand Up @@ -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,
Expand Down
30 changes: 2 additions & 28 deletions net/colo-compare.c
View file
Expand Up @@ -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.
Expand All @@ -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;
}
Expand Down
41 changes: 7 additions & 34 deletions net/vhost-user.c
View file
Expand Up @@ -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);
Expand Down Expand Up @@ -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;
}
Expand Down Expand Up @@ -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;
}
Expand Down
22 changes: 19 additions & 3 deletions qemu-char.c
View file
Expand Up @@ -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);
Expand All @@ -4005,7 +4004,6 @@ CharDriverState *qemu_chr_new_from_opts(QemuOpts *opts,
return chr;

err:
qemu_opts_del(opts);
return NULL;
}

Expand Down Expand Up @@ -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;
}

Expand Down Expand Up @@ -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);
}
Expand Down Expand Up @@ -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;
Expand Down Expand Up @@ -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)
{
Expand Down

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