vnc: fix crash when vnc_server_info_get has an error

The vnc_server_info_get will allocate the VncServerInfo
struct and then call vnc_init_basic_info_from_server_addr
to populate the basic fields. If this returns an error
though, the qapi_free_VncServerInfo call will then crash
because the VncServerInfo struct instance was not properly
NULL-initialized and thus contains random stack garbage.

 #0  0x00007f1987c8e6f5 in raise () at /lib64/libc.so.6
 #1  0x00007f1987c902fa in abort () at /lib64/libc.so.6
 #2  0x00007f1987ccf600 in __libc_message () at /lib64/libc.so.6
 #3  0x00007f1987cd7d4a in _int_free () at /lib64/libc.so.6
 #4  0x00007f1987cdb2ac in free () at /lib64/libc.so.6
 #5  0x00007f198b654f6e in g_free () at /lib64/libglib-2.0.so.0
 #6  0x0000559193cdcf54 in visit_type_str (v=v@entry=
     0x5591972f14b0, name=name@entry=0x559193de1e29 "host", obj=obj@entry=0x5591961dbfa0, errp=errp@entry=0x7fffd7899d80)
     at qapi/qapi-visit-core.c:255
 #7  0x0000559193cca8f3 in visit_type_VncBasicInfo_members (v=v@entry=
     0x5591972f14b0, obj=obj@entry=0x5591961dbfa0, errp=errp@entry=0x7fffd7899dc0) at qapi-visit.c:12307
 #8  0x0000559193ccb523 in visit_type_VncServerInfo_members (v=v@entry=
     0x5591972f14b0, obj=0x5591961dbfa0, errp=errp@entry=0x7fffd7899e00) at qapi-visit.c:12632
 #9  0x0000559193ccb60b in visit_type_VncServerInfo (v=v@entry=
     0x5591972f14b0, name=name@entry=0x0, obj=obj@entry=0x7fffd7899e48, errp=errp@entry=0x0) at qapi-visit.c:12658
 #10 0x0000559193cb53d8 in qapi_free_VncServerInfo (obj=<optimized out>) at qapi-types.c:3970
 #11 0x0000559193c1e6ba in vnc_server_info_get (vd=0x7f1951498010) at ui/vnc.c:233
 #12 0x0000559193c24275 in vnc_connect (vs=0x559197b2f200, vs=0x559197b2f200, event=QAPI_EVENT_VNC_CONNECTED) at ui/vnc.c:284
 #13 0x0000559193c24275 in vnc_connect (vd=vd@entry=0x7f1951498010, sioc=sioc@entry=0x559196bf9c00, skipauth=skipauth@entry=tru e, websocket=websocket@entry=false) at ui/vnc.c:3039
 #14 0x0000559193c25806 in vnc_display_add_client (id=<optimized out>, csock=<optimized out>, skipauth=<optimized out>)
     at ui/vnc.c:3877
 #15 0x0000559193a90c28 in qmp_marshal_add_client (args=<optimized out>, ret=<optimized out>, errp=0x7fffd7899f90)
     at qmp-marshal.c:105
 #16 0x000055919399c2b7 in handle_qmp_command (parser=<optimized out>, tokens=<optimized out>)
     at /home/berrange/src/virt/qemu/monitor.c:3971
 #17 0x0000559193ce3307 in json_message_process_token (lexer=0x559194ab0838, input=0x559194a6d940, type=JSON_RCURLY, x=111, y=1 2) at qobject/json-streamer.c:105
 #18 0x0000559193cfa90d in json_lexer_feed_char (lexer=lexer@entry=0x559194ab0838, ch=125 '}', flush=flush@entry=false)
     at qobject/json-lexer.c:319
 #19 0x0000559193cfaa1e in json_lexer_feed (lexer=0x559194ab0838, buffer=<optimized out>, size=<optimized out>)
     at qobject/json-lexer.c:369
 #20 0x0000559193ce33c9 in json_message_parser_feed (parser=<optimized out>, buffer=<optimized out>, size=<optimized out>)
     at qobject/json-streamer.c:124
 #21 0x000055919399a85b in monitor_qmp_read (opaque=<optimized out>, buf=<optimized out>, size=<optimized out>)
     at /home/berrange/src/virt/qemu/monitor.c:3987
 #22 0x0000559193a87d00 in tcp_chr_read (chan=<optimized out>, cond=<optimized out>, opaque=0x559194a7d900)
     at qemu-char.c:2895
 #23 0x00007f198b64f703 in g_main_context_dispatch () at /lib64/libglib-2.0.so.0
 #24 0x0000559193c484b3 in main_loop_wait () at main-loop.c:213
 #25 0x0000559193c484b3 in main_loop_wait (timeout=<optimized out>) at main-loop.c:258
 #26 0x0000559193c484b3 in main_loop_wait (nonblocking=<optimized out>) at main-loop.c:506
 #27 0x0000559193964c55 in main () at vl.c:1908
 #28 0x0000559193964c55 in main (argc=<optimized out>, argv=<optimized out>, envp=<optimized out>) at vl.c:4603

This was introduced in

  commit 98481bfcd661daa3c160cc87a297b0e60a307788
  Author: Eric Blake <eblake@redhat.com>
  Date:   Mon Oct 26 16:34:45 2015 -0600

    vnc: Hoist allocation of VncBasicInfo to callers

which added error reporting for vnc_init_basic_info_from_server_addr
but didn't change the g_malloc calls to g_malloc0.

Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
Message-id: 1470134726-15697-3-git-send-email-berrange@redhat.com
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
