[Spice-devel] [PATCH] server/red_worker: fix use after free for listeners

[Alon Levy]

This fixes a core dumped observed once by repeated migration. So far 100
migrations and no recurrence.

Core was generated by `/home/alon/spice/upstream/bin/qemu-system-x86_64 --enable-kvm -qmp unix:/tmp/mi'.
Program terminated with signal 11, Segmentation fault.
11197	                if (evt_listener && evt_listener->refs > 1) {
Missing separate debuginfos, use: debuginfo-install bluez-libs-4.98-3.fc17.x86_64 brlapi-0.5.6-4.fc17.x86_64 bzip2-libs-1.0.6-4.fc17.x86_64 cryptopp-5.6.1-6.fc17.x86_64 keyutils-libs-1.5.5-2.fc17.x86_64 libssh2-1.4.0-1.fc17.x86_64 nss-softokn-freebl-3.13.1-20.fc17.x86_64 xen-libs-4.1.2-11.fc17.x86_64 xz-libs-5.1.1-2alpha.fc17.x86_64
(gdb) bt
(gdb) l
11192	        for (i = 0; i < MAX_EVENT_SOURCES; i++) {
11193	            struct pollfd *pfd = worker.poll_fds + i;
11194	            if (pfd->revents) {
11195	                EventListener *evt_listener = worker.listeners[i];
11196
11197	                if (evt_listener && evt_listener->refs > 1) {
11198	                    evt_listener->action(evt_listener, pfd);
11199	                    if (--evt_listener->refs) {
11200	                        continue;
11201	                    }
(gdb) p evt_listener
$1 = (EventListener *) 0x7f15a9a5d1e0
(gdb) p *evt_listener
Cannot access memory at address 0x7f15a9a5d1e0
(gdb) p i
$2 = 2
(gdb) p worker.listeners
$3 = {0x7f15bc832520, 0x7f15a406e1a0, 0x7f15a9a5d1e0, 0x0 <repeats 17 times>}
---
 server/red_worker.c |    3 ++-
 1 files changed, 2 insertions(+), 1 deletions(-)

diff --git a/server/red_worker.c b/server/red_worker.c
index e88dbc0..a2f31c0 100644
--- a/server/red_worker.c
+++ b/server/red_worker.c
@@ -11194,7 +11194,7 @@ void *red_worker_main(void *arg)
             if (pfd->revents) {
                 EventListener *evt_listener = worker.listeners[i];
 
-                if (evt_listener->refs > 1) {
+                if (evt_listener && evt_listener->refs > 1) {
                     evt_listener->action(evt_listener, pfd);
                     if (--evt_listener->refs) {
                         continue;
@@ -11202,6 +11202,7 @@ void *red_worker_main(void *arg)
                 }
                 red_printf("freeing event listener");
                 evt_listener->free(evt_listener);
+                worker.listeners[i] = NULL;
             }
         }
 
-- 
1.7.9.1