[PATCH] randr: clear primary screen's primaryOutput when the output is deleted

[hongao]

This fix use after free when a pluggable gpu screen (such as displaylink)
was set as primary screen and unpluged.

gdb backtrace:
 #0 OssigHandler (signo=11, sip=0x7fff2e0a50f0, unused=0x7fff2e0a4fc0) at ../../../../os/osinit.c:138
 #1 <signal handler called>
 #2 rrGetscreenResources (client=0x3195160, query=0) at ../../../../randr/rrscreen.c:577
 #3 0x0000000000562bae in ProcRRGetscreenResourcesCurrent (client=0x3195160) at ../../../../randr/rrscreen.c:652
 #4 OxOOOOB0000054de63 in ProcRRDispatch (client=0x3195160) at ../../../../randr/randr.c:717
 #5 0x00000000004322c6 in Dispatch () at ../../../../dix/dispatch.c:485
 #6 0x0900900990443139 in dix_main (argc=12, argv=0x7fff2e0a5f78, envp=0x7fff2e0a5fe0) at ../../../../dix/main.c:276
 #7 0X0000000000421d9a in main (argc=12, argv=0x7fff2e0a5f78, envp=0x7fff2e0a5fe0) at ../../../../dix/stubmain.c:34

Signed-off-by: hongao <hongao at uniontech.com>
---
 randr/rroutput.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/randr/rroutput.c b/randr/rroutput.c
index 0b4639aa6..755fccc75 100644
--- a/randr/rroutput.c
+++ b/randr/rroutput.c
@@ -377,6 +377,8 @@ RROutputDestroyResource(void *value, XID pid)
 {
     RROutputPtr output = (RROutputPtr) value;
     ScreenPtr pScreen = output->pScreen;
+    ScreenPtr primary;
+    rrScrPrivPtr primarysp;
     int m;
 
     if (pScreen) {
@@ -397,6 +399,15 @@ RROutputDestroyResource(void *value, XID pid)
         if (pScrPriv->primaryOutput == output)
             pScrPriv->primaryOutput = NULL;
 
+        if (pScreen->isGPU) {
+            primary = pScreen->current_primary;
+            if (primary) {
+                primarysp = rrGetScrPriv(primary);
+                if(primarysp->primaryOutput == output)
+                    primarysp->primaryOutput = NULL;
+            }
+        }
+
         for (i = 0; i < pScrPriv->numOutputs; i++) {
             if (pScrPriv->outputs[i] == output) {
                 memmove(pScrPriv->outputs + i, pScrPriv->outputs + i + 1,
-- 
2.33.1