smartcard: add a ref to item before adding to pipe
smartcard: add a ref to item before adding to pipe

There is an unref when the message is sent.
This is related to CVE-2016-0749

==17204== ERROR: AddressSanitizer: heap-use-after-free on address 0x6008000144a8 at pc 0x7fffee0ce245 bp 0x7fffffffc630 sp 0x7fffffffc620
READ of size 4 at 0x6008000144a8 thread T0
    #0 0x7fffee0ce244 in smartcard_unref_vsc_msg_item /home/elmarco/src/spice/spice/server/smartcard.c:608
    #1 0x7fffee0cb451 in smartcard_unref_msg_to_client /home/elmarco/src/spice/spice/server/smartcard.c:178
    #2 0x7fffedfcdf14 in spice_char_device_read_from_device /home/elmarco/src/spice/spice/server/char-device.c:330
    #3 0x7fffedfd1763 in spice_char_device_wakeup /home/elmarco/src/spice/spice/server/char-device.c:901
    #4 0x7fffee05da98 in spice_server_char_device_wakeup /home/elmarco/src/spice/spice/server/reds.c:2990
    #5 0x55555593fa34 in spice_chr_write /home/elmarco/src/qemu/spice-qemu-char.c:189
    #6 0x5555559375f1 in qemu_chr_fe_write /home/elmarco/src/qemu/qemu-char.c:220
    #7 0x555555b3b682 in ccid_card_vscard_send_msg.isra.2 /home/elmarco/src/qemu/hw/usb/ccid-card-passthru.c:76
    #8 0x555555b3c466 in ccid_card_vscard_send_error /home/elmarco/src/qemu/hw/usb/ccid-card-passthru.c:91
    #9 0x555555b3c466 in ccid_card_vscard_handle_message /home/elmarco/src/qemu/hw/usb/ccid-card-passthru.c:242
    #10 0x555555b3c466 in ccid_card_vscard_read /home/elmarco/src/qemu/hw/usb/ccid-card-passthru.c:289
    #11 0x55555593f169 in vmc_write /home/elmarco/src/qemu/spice-qemu-char.c:41
    #12 0x7fffedfcee6d in spice_char_device_write_to_device /home/elmarco/src/spice/spice/server/char-device.c:477
    #13 0x7fffedfcfd31 in spice_char_device_write_buffer_add /home/elmarco/src/spice/spice/server/char-device.c:629
    #14 0x7fffee0ce9df in smartcard_channel_write_to_reader /home/elmarco/src/spice/spice/server/smartcard.c:675
    #15 0x7fffee0cc7db in smartcard_char_device_notify_reader_add /home/elmarco/src/spice/spice/server/smartcard.c:341
    #16 0x7fffee0ce4f3 in smartcard_add_reader /home/elmarco/src/spice/spice/server/smartcard.c:648
    #17 0x7fffee0cf2e2 in smartcard_channel_handle_message /home/elmarco/src/spice/spice/server/smartcard.c:763
    #18 0x7fffedffe21f in red_peer_handle_incoming /home/elmarco/src/spice/spice/server/red-channel.c:307
    #19 0x7fffedffe4f6 in red_channel_client_receive /home/elmarco/src/spice/spice/server/red-channel.c:325
    #20 0x7fffee00726c in red_channel_client_event /home/elmarco/src/spice/spice/server/red-channel.c:1566
    #21 0x555555c3c53d in qemu_iohandler_poll /home/elmarco/src/qemu/iohandler.c:143
    #22 0x555555c3b800 in main_loop_wait /home/elmarco/src/qemu/main-loop.c:504
    #23 0x5555556f160c in main_loop /home/elmarco/src/qemu/vl.c:1818
    #24 0x5555556f160c in main /home/elmarco/src/qemu/vl.c:4394
    #25 0x7fffed7d0b14 in __libc_start_main /usr/src/debug/glibc-2.17-c758a686/csu/libc-start.c:274
    #26 0x5555556f9c20 in _start (/home/elmarco/src/qemu/x86_64-softmmu/qemu-system-x86_64+0x1a5c20)
0x6008000144a8 is located 24 bytes inside of 40-byte region [0x600800014490,0x6008000144b8)
freed by thread T0 here:
    #0 0x7ffff4e61009 in __interceptor_free /usr/src/debug/gcc-4.8.5-20150702/obj-x86_64-redhat-linux/x86_64-redhat-linux/libsanitizer/asan/../../../../libsanitizer/asan/asan_malloc_linux.cc:61
    #1 0x7fffee0ce2a1 in smartcard_unref_vsc_msg_item /home/elmarco/src/spice/spice/server/smartcard.c:610
    #2 0x7fffee0cdd58 in smartcard_channel_release_pipe_item /home/elmarco/src/spice/spice/server/smartcard.c:548
    #3 0x7fffee000668 in red_channel_client_release_item /home/elmarco/src/spice/spice/server/red-channel.c:602
    #4 0x7fffee0006ef in red_channel_client_release_sent_item /home/elmarco/src/spice/spice/server/red-channel.c:609
    #5 0x7fffee0007b5 in red_channel_peer_on_out_msg_done /home/elmarco/src/spice/spice/server/red-channel.c:620
    #6 0x7fffedffed7e in red_peer_handle_outgoing /home/elmarco/src/spice/spice/server/red-channel.c:385
    #7 0x7fffee0057bb in red_channel_client_send /home/elmarco/src/spice/spice/server/red-channel.c:1294
    #8 0x7fffee0076e6 in red_channel_client_begin_send_message /home/elmarco/src/spice/spice/server/red-channel.c:1605
    #9 0x7fffee0cdccd in smartcard_channel_send_item /home/elmarco/src/spice/spice/server/smartcard.c:541
    #10 0x7fffee000570 in red_channel_client_send_item /home/elmarco/src/spice/spice/server/red-channel.c:588
    #11 0x7fffee005bfb in red_channel_client_push /home/elmarco/src/spice/spice/server/red-channel.c:1347
    #12 0x7fffee007ef7 in red_channel_client_pipe_add_push /home/elmarco/src/spice/spice/server/red-channel.c:1673
    #13 0x7fffee0cde4d in smartcard_channel_client_pipe_add_push /home/elmarco/src/spice/spice/server/smartcard.c:571
    #14 0x7fffee0cb567 in smartcard_send_msg_to_client /home/elmarco/src/spice/spice/server/smartcard.c:187
    #15 0x7fffedfcdba2 in spice_char_device_send_msg_to_clients /home/elmarco/src/spice/spice/server/char-device.c:282
    #16 0x7fffedfcdea4 in spice_char_device_read_from_device /home/elmarco/src/spice/spice/server/char-device.c:329
    #17 0x7fffedfd1763 in spice_char_device_wakeup /home/elmarco/src/spice/spice/server/char-device.c:901
    #18 0x7fffee05da98 in spice_server_char_device_wakeup /home/elmarco/src/spice/spice/server/reds.c:2990
    #19 0x55555593fa34 in spice_chr_write /home/elmarco/src/qemu/spice-qemu-char.c:189

Signed-off-by: Marc-Andre Lureau <a6f2b960a4aca61381fc650a67901b2ac8e83e6d@redhat.com>

fgouget/spice,fgouget/spice,fgouget/spice,fgouget/spice