block/nbd: fix memory leak in nbd_open()

In currently implementation there will be a memory leak when
nbd_client_connect() returns error status. Here is an easy way to
reproduce:

1. run qemu-iotests as follow and check the result with asan:
    ./check -raw 143

Following is the asan output backtrack:
Direct leak of 40 byte(s) in 1 object(s) allocated from:
    #0 0x7f629688a560 in calloc (/usr/lib64/libasan.so.3+0xc7560)
    kata-containers#1 0x7f6295e7e015 in g_malloc0  (/usr/lib64/libglib-2.0.so.0+0x50015)
    kata-containers#2 0x56281dab4642 in qobject_input_start_struct  /mnt/sdb/qemu-4.2.0-rc0/qapi/qobject-input-visitor.c:295
    kata-containers#3 0x56281dab1a04 in visit_start_struct  /mnt/sdb/qemu-4.2.0-rc0/qapi/qapi-visit-core.c:49
    kata-containers#4 0x56281dad1827 in visit_type_SocketAddress  qapi/qapi-visit-sockets.c:386
    kata-containers#5 0x56281da8062f in nbd_config   /mnt/sdb/qemu-4.2.0-rc0/block/nbd.c:1716
    kata-containers#6 0x56281da8062f in nbd_process_options /mnt/sdb/qemu-4.2.0-rc0/block/nbd.c:1829
    kata-containers#7 0x56281da8062f in nbd_open /mnt/sdb/qemu-4.2.0-rc0/block/nbd.c:1873

Direct leak of 15 byte(s) in 1 object(s) allocated from:
    #0 0x7f629688a3a0 in malloc (/usr/lib64/libasan.so.3+0xc73a0)
    kata-containers#1 0x7f6295e7dfbd in g_malloc (/usr/lib64/libglib-2.0.so.0+0x4ffbd)
    kata-containers#2 0x7f6295e96ace in g_strdup (/usr/lib64/libglib-2.0.so.0+0x68ace)
    kata-containers#3 0x56281da804ac in nbd_process_options /mnt/sdb/qemu-4.2.0-rc0/block/nbd.c:1834
    kata-containers#4 0x56281da804ac in nbd_open /mnt/sdb/qemu-4.2.0-rc0/block/nbd.c:1873

Indirect leak of 24 byte(s) in 1 object(s) allocated from:
    #0 0x7f629688a3a0 in malloc (/usr/lib64/libasan.so.3+0xc73a0)
    kata-containers#1 0x7f6295e7dfbd in g_malloc (/usr/lib64/libglib-2.0.so.0+0x4ffbd)
    kata-containers#2 0x7f6295e96ace in g_strdup (/usr/lib64/libglib-2.0.so.0+0x68ace)
    kata-containers#3 0x56281dab41a3 in qobject_input_type_str_keyval /mnt/sdb/qemu-4.2.0-rc0/qapi/qobject-input-visitor.c:536
    kata-containers#4 0x56281dab2ee9 in visit_type_str /mnt/sdb/qemu-4.2.0-rc0/qapi/qapi-visit-core.c:297
    kata-containers#5 0x56281dad0fa1 in visit_type_UnixSocketAddress_members qapi/qapi-visit-sockets.c:141
    kata-containers#6 0x56281dad17b6 in visit_type_SocketAddress_members qapi/qapi-visit-sockets.c:366
    kata-containers#7 0x56281dad186a in visit_type_SocketAddress qapi/qapi-visit-sockets.c:393
    kata-containers#8 0x56281da8062f in nbd_config /mnt/sdb/qemu-4.2.0-rc0/block/nbd.c:1716
    kata-containers#9 0x56281da8062f in nbd_process_options /mnt/sdb/qemu-4.2.0-rc0/block/nbd.c:1829
    kata-containers#10 0x56281da8062f in nbd_open /mnt/sdb/qemu-4.2.0-rc0/block/nbd.c:1873

Fixes: 8f071c9
Reported-by: Euler Robot <[email protected]>
Signed-off-by: Pan Nengyuan <[email protected]>
Reviewed-by: Vladimir Sementsov-Ogievskiy <[email protected]>
Cc: qemu-stable <[email protected]>
Cc: Vladimir Sementsov-Ogievskiy <[email protected]>
Message-Id: <[email protected]>
Reviewed-by: Stefano Garzarella <[email protected]>
Signed-off-by: Eric Blake <[email protected]>

block/nbd.c

@@ -1915,6 +1915,7 @@ static int nbd_open(BlockDriverState *bs, QDict *options, int flags,
 
     ret = nbd_client_connect(bs, errp);
     if (ret < 0) {
+        nbd_clear_bdrvstate(s);
         return ret;
     }
     /* successfully connected */