[Spice-devel] [PATCH 1/2 v3] remove dangling pointer for RedCharDeviceVDIPort

Fri May 6 09:55:22 UTC 2016

Hey,

On Thu, May 05, 2016 at 05:03:58PM +0100, Frediano Ziglio wrote:
> When a client disconnects remove it from the list of clients connected
> to the spice char-device.
>
> This was caused by commit 1cec1c5118b65124de6bc6f984f376ff4e297bfb
> ("reds: Make VDIPortState a GObject") as the lifespan of RedCharDevice
> was changed.
>
> This could be reproduced with:
> - start rhel7 machine
> - connect remote viewer (RV)
> - RV: login
> - connect ssh
> - SSH: stop agent
> - disconnect RV
> - SSH: start agent
> - connect to RV

Not sure if this is quite fixed yet. From latest upstream (with this patch), I
can manage to crash the guest with:

Program received signal SIGSEGV, Segmentation fault.
0x00007fdfb4fed556 in vdi_port_read_one_msg_from_device (sin=0x5603d2a36c68, opaque=<optimized out>) at reds.c:840
840         g_assert(RED_CHAR_DEVICE(reds->agent_dev) == sin->st);
(gdb) bt
#0  0x00007fdfb4fed556 in vdi_port_read_one_msg_from_device (sin=0x5603d2a36c68, opaque=<optimized out>) at reds.c:840
#1  0x00007fdfb4faad41 in red_char_device_read_from_device (dev=0x5603d2a3b150) at char-device.c:103
#2  0x00007fdfb4faad41 in red_char_device_read_from_device (dev=0x5603d2a3b150) at char-device.c:347
#3  0x00007fdfb4fad67c in red_char_device_start (dev=0x5603d2a3b150) at char-device.c:810
#4  0x00007fdfb4fe9d38 in spice_server_vm_start (reds=0x5603d2af7300) at reds.c:4071
#5  0x00005603cfc22a49 in qdev_reset_one ()
#6  0x00005603cfc22358 in qbus_walk_children ()
#7  0x00005603cfc22288 in qdev_walk_children ()
#8  0x00005603cfc22358 in qbus_walk_children ()
#9  0x00005603cfbb9a9a in qemu_system_reset ()
#10 0x00005603cfaaf264 in main ()

...

The agent restart also crashes the client which is what I'm focusing in fix at
the moment... Happy crash Friday!

Cheers,
  toso

>
> and caused (using address sanitizer):
> 
> main_channel_handle_parsed: agent start
> =================================================================
> ==29592==ERROR: AddressSanitizer: heap-use-after-free on address 0x60c00001cff0 at pc 0x7fa85b6e8595 bp 0x7ffde3801940 sp 0x7ffde3801930
> READ of size 8 at 0x60c00001cff0 thread T0
>     #0 0x7fa85b6e8594 in red_client_get_main /home/freddy/work/spice-server/server/red-channel.c:2190
>     #1 0x7fa85b7311e6 in vdi_port_send_msg_to_client /home/freddy/work/spice-server/server/reds.c:880
>     #2 0x7fa85b69383e in red_char_device_send_msg_to_client /home/freddy/work/spice-server/server/char-device.c:138
>     #3 0x7fa85b69383e in red_char_device_send_msg_to_clients /home/freddy/work/spice-server/server/char-device.c:356
>     #4 0x7fa85b69383e in red_char_device_read_from_device /home/freddy/work/spice-server/server/char-device.c:403
>     #5 0x55a2633b81c1  (/usr/bin/qemu-system-x86_64+0x5561c1)
>     #6 0x55a2633afe7a  (/usr/bin/qemu-system-x86_64+0x54de7a)
>     #7 0x55a2634cb7b1  (/usr/bin/qemu-system-x86_64+0x6697b1)
>     #8 0x55a2632078d0  (/usr/bin/qemu-system-x86_64+0x3a58d0)
>     #9 0x55a26379b2e8  (/usr/bin/qemu-system-x86_64+0x9392e8)
>     #10 0x55a26379a7a0  (/usr/bin/qemu-system-x86_64+0x9387a0)
>     #11 0x55a26313fb78 in main (/usr/bin/qemu-system-x86_64+0x2ddb78)
>     #12 0x7fa85a3cc57f in __libc_start_main (/lib64/libc.so.6+0x2057f)
>     #13 0x55a26314b0c8  (/usr/bin/qemu-system-x86_64+0x2e90c8)
> 
> 0x60c00001cff0 is located 48 bytes inside of 128-byte region [0x60c00001cfc0,0x60c00001d040)
> freed by thread T0 here:
>     #0 0x7fa869e3667a in __interceptor_free (/lib64/libasan.so.2+0x9867a)
>     #1 0x7fa85b6d75f7 in red_client_unref /home/freddy/work/spice-server/server/red-channel.c:2076
>     #2 0x7fa85b6ead74 in dispatcher_handle_single_read /home/freddy/work/spice-server/server/dispatcher.c:291
>     #3 0x7fa85b6ead74 in dispatcher_handle_recv_read /home/freddy/work/spice-server/server/dispatcher.c:314
>     #4 0x55a26379b2e8  (/usr/bin/qemu-system-x86_64+0x9392e8)
>     #5 0x55a26379a7a0  (/usr/bin/qemu-system-x86_64+0x9387a0)
>     #6 0x55a26313fb78 in main (/usr/bin/qemu-system-x86_64+0x2ddb78)
>     #7 0x7fa85a3cc57f in __libc_start_main (/lib64/libc.so.6+0x2057f)
> 
> previously allocated by thread T0 here:
>     #0 0x7fa869e36b19 in __interceptor_calloc (/lib64/libasan.so.2+0x98b19)
>     #1 0x7fa85b7d6858 in spice_malloc0 /home/freddy/work/spice-server/spice-common/common/mem.c:109
>     #2 0x7fa85b6e760c in red_client_new /home/freddy/work/spice-server/server/red-channel.c:2053
>     #3 0x7fa85b7449e4 in reds_handle_main_link /home/freddy/work/spice-server/server/reds.c:1762
>     #4 0x7fa85b7449e4 in reds_handle_link /home/freddy/work/spice-server/server/reds.c:2002
>     #5 0x7fa85b745d3a in reds_handle_ticket /home/freddy/work/spice-server/server/reds.c:2056
>     #6 0x55a26379b2e8  (/usr/bin/qemu-system-x86_64+0x9392e8)
>     #7 0x55a26379a7a0  (/usr/bin/qemu-system-x86_64+0x9387a0)
>     #8 0x55a26313fb78 in main (/usr/bin/qemu-system-x86_64+0x2ddb78)
>     #9 0x7fa85a3cc57f in __libc_start_main (/lib64/libc.so.6+0x2057f)
> 
> SUMMARY: AddressSanitizer: heap-use-after-free /home/freddy/work/spice-server/server/red-channel.c:2190 red_client_get_main
> Shadow bytes around the buggy address:
>   0x0c187fffb9a0: fd fd fd fd fd fd fd fd fa fa fa fa fa fa fa fa
>   0x0c187fffb9b0: fd fd fd fd fd fd fd fd fd fd fd fd fd fd fd fd
>   0x0c187fffb9c0: fa fa fa fa fa fa fa fa fd fd fd fd fd fd fd fd
>   0x0c187fffb9d0: fd fd fd fd fd fd fd fd fa fa fa fa fa fa fa fa
>   0x0c187fffb9e0: fd fd fd fd fd fd fd fd fd fd fd fd fd fd fd fd
> =>0x0c187fffb9f0: fa fa fa fa fa fa fa fa fd fd fd fd fd fd[fd]fd
>   0x0c187fffba00: fd fd fd fd fd fd fd fd fa fa fa fa fa fa fa fa
>   0x0c187fffba10: fd fd fd fd fd fd fd fd fd fd fd fd fd fd fd fd
>   0x0c187fffba20: fa fa fa fa fa fa fa fa fd fd fd fd fd fd fd fd
>   0x0c187fffba30: fd fd fd fd fd fd fd fd fa fa fa fa fa fa fa fa
>   0x0c187fffba40: fd fd fd fd fd fd fd fd fd fd fd fd fd fd fd fd
> 
> Signed-off-by: Frediano Ziglio <fziglio at redhat.com>
> ---
>  server/reds.c | 10 ++++------
>  1 file changed, 4 insertions(+), 6 deletions(-)
> 
> Changes from v2:
> - added a comment from Uri Lublin.
> 
> diff --git a/server/reds.c b/server/reds.c
> index efd1429..67c262a 100644
> --- a/server/reds.c
> +++ b/server/reds.c
> @@ -603,12 +603,10 @@ void reds_client_disconnect(RedsState *reds, RedClient *client)
>          reds_mig_remove_wait_disconnect_client(reds, client);
>      }
>  
> -    if (reds->agent_dev->priv->agent_attached) {
> -        /* note that vdagent might be NULL, if the vdagent was once
> -         * up and than was removed */
> -        if (red_char_device_client_exists(RED_CHAR_DEVICE(reds->agent_dev), client)) {
> -            red_char_device_client_remove(RED_CHAR_DEVICE(reds->agent_dev), client);
> -        }
> +    /* note that client might be NULL, if the vdagent was once
> +     * up and than was removed */
> +    if (red_char_device_client_exists(RED_CHAR_DEVICE(reds->agent_dev), client)) {
> +        red_char_device_client_remove(RED_CHAR_DEVICE(reds->agent_dev), client);
>      }
>  
>      ring_remove(&client->link);
> -- 
> 2.5.5
> 
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