[Spice-devel] [spice-server] Add some NULL checks to spice_server_remove_interface()

[Christophe Fergeau]

Currently, calling spice_server_remove_interface() twice in a row with
the same SPICE_INTERFACE_CHAR_DEVICE is going to cause a crash when
calling red_char_device_get_server(char_device->st); because
char_device->st will have been set to NULL by the first call.

This commit adds a few sanity checks before trying to use the various
'st' members of the interfaces.

This should avoid the crash described in
https://bugzilla.redhat.com/show_bug.cgi?id=1411194 even though it's not
clear how we got in that situation.
---
 server/reds.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/server/reds.c b/server/reds.c
index 29485a8..90d126d 100644
--- a/server/reds.c
+++ b/server/reds.c
@@ -3307,8 +3307,11 @@ SPICE_GNUC_VISIBLE int spice_server_remove_interface(SpiceBaseInstance *sin)
     RedsState *reds;
     const SpiceBaseInterface *interface = sin->sif;
 
+    g_return_val_if_fail(sin != NULL, -2);
+
     if (strcmp(interface->type, SPICE_INTERFACE_TABLET) == 0) {
         SpiceTabletInstance *tablet = SPICE_CONTAINEROF(sin, SpiceTabletInstance, base);
+        g_return_val_if_fail(tablet->st != NULL, -2);
         reds = spice_tablet_state_get_server(tablet->st);
         spice_info("remove SPICE_INTERFACE_TABLET");
         inputs_channel_detach_tablet(reds->inputs_channel, tablet);
@@ -3321,12 +3324,14 @@ SPICE_GNUC_VISIBLE int spice_server_remove_interface(SpiceBaseInstance *sin)
         snd_detach_record(SPICE_CONTAINEROF(sin, SpiceRecordInstance, base));
     } else if (strcmp(interface->type, SPICE_INTERFACE_CHAR_DEVICE) == 0) {
         SpiceCharDeviceInstance *char_device = SPICE_CONTAINEROF(sin, SpiceCharDeviceInstance, base);
+        g_return_val_if_fail(char_device->st != NULL, -2);
         reds = red_char_device_get_server(char_device->st);
         spice_server_char_device_remove_interface(reds, sin);
     } else if (strcmp(interface->type, SPICE_INTERFACE_QXL) == 0) {
         QXLInstance *qxl;
 
         qxl = SPICE_CONTAINEROF(sin, QXLInstance, base);
+        g_return_val_if_fail(qxl->st != NULL, -2);
         reds = red_qxl_get_server(qxl->st);
         reds->qxl_instances = g_list_remove(reds->qxl_instances, qxl);
         red_qxl_destroy(qxl);
-- 
2.9.3