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

[Frediano Ziglio]

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

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