[Qemu-devel] [PATCH] qemu-nbd: NULL nbd export pointer dereference after kill (TERMINATE)

[Zhang Haoyu]

After receive TERMINATE signal, qemu nbd state is set to TERMINATE, then in the 
main loop, 
nbd_export_close -> nbd_export_put is performed, but sometimes exp->refcount 
still greater than zero after nbd_export_put,
so the qemu nbd state has not been set to TERMINATED, then in next cycle,  NULL 
exp will be dereference.
    do {
        main_loop_wait(false);
        if (state == TERMINATE) {
            state = TERMINATING;
            nbd_export_close(exp);
            nbd_export_put(exp);
            exp = NULL;
        }
    } while (state != TERMINATED);

Signed-off-by: Zhang Haoyu <zhan...@sangfor.com>
---
 blockdev-nbd.c      | 5 +++--
 include/block/nbd.h | 2 +-
 nbd.c               | 5 ++++-
 qemu-nbd.c          | 6 +++---
 4 files changed, 11 insertions(+), 7 deletions(-)

diff --git a/blockdev-nbd.c b/blockdev-nbd.c
index b3a2474..c339081 100644
--- a/blockdev-nbd.c
+++ b/blockdev-nbd.c
@@ -65,8 +65,9 @@ static void nbd_close_notifier(Notifier *n, void *data)
     notifier_remove(&cn->n);
     QTAILQ_REMOVE(&close_notifiers, cn, next);
 
-    nbd_export_close(cn->exp);
-    nbd_export_put(cn->exp);
+    do {
+        cn->exp = nbd_export_put(cn->exp);
+    } while (cn->exp);
     g_free(cn);
 }
 
diff --git a/include/block/nbd.h b/include/block/nbd.h
index 9e835d2..1912ef0 100644
--- a/include/block/nbd.h
+++ b/include/block/nbd.h
@@ -90,7 +90,7 @@ NBDExport *nbd_export_new(BlockDriverState *bs, off_t 
dev_offset,
                           void (*close)(NBDExport *));
 void nbd_export_close(NBDExport *exp);
 void nbd_export_get(NBDExport *exp);
-void nbd_export_put(NBDExport *exp);
+NBDExport *nbd_export_put(NBDExport *exp);
 
 BlockDriverState *nbd_export_get_blockdev(NBDExport *exp);
 
diff --git a/nbd.c b/nbd.c
index e7d1cee..2fccba5 100644
--- a/nbd.c
+++ b/nbd.c
@@ -991,7 +991,7 @@ void nbd_export_get(NBDExport *exp)
     exp->refcount++;
 }
 
-void nbd_export_put(NBDExport *exp)
+NBDExport *nbd_export_put(NBDExport *exp)
 {
     assert(exp->refcount > 0);
     if (exp->refcount == 1) {
@@ -1006,7 +1006,10 @@ void nbd_export_put(NBDExport *exp)
         }
 
         g_free(exp);
+        return NULL;
     }
+
+    return exp;
 }
 
 BlockDriverState *nbd_export_get_blockdev(NBDExport *exp)
diff --git a/qemu-nbd.c b/qemu-nbd.c
index 626e584..e1f3577 100644
--- a/qemu-nbd.c
+++ b/qemu-nbd.c
@@ -735,9 +735,9 @@ int main(int argc, char **argv)
         main_loop_wait(false);
         if (state == TERMINATE) {
             state = TERMINATING;
-            nbd_export_close(exp);
-            nbd_export_put(exp);
-            exp = NULL;
+            do {
+                exp = nbd_export_put(exp);
+            } while (exp);
         }
     } while (state != TERMINATED);
 
-- 
1.9.4.msysgit.0