[SCSI] virtio_scsi: fix TMF use-after-free

Fix a use-after-free in the TMF path, where cmd may have been already
freed by virtscsi_complete_free when wait_for_completion restarts
executing virtscsi_tmf.  Technically a race, but in practice the command
will always be freed long before the completion waiter is awoken.

The fix is to make callers specifying a completion responsible for
freeing the command in all cases.

Signed-off-by: Hu Tao <hutao@cn.fujitsu.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: James Bottomley <JBottomley@Parallels.com>

diff --git a/drivers/scsi/virtio_scsi.c b/drivers/scsi/virtio_scsi.c
index efccd72c4a3eeb6bffe7969c8587d87d93e9771e..1b384311726897bff5ba3e1014a53a536eccc210 100644 (file)
--- a/drivers/scsi/virtio_scsi.c
+++ b/drivers/scsi/virtio_scsi.c
@@ -175,7 +175,8 @@ static void virtscsi_complete_free(void *buf)
 
        if (cmd->comp)
                complete_all(cmd->comp);
-       mempool_free(cmd, virtscsi_cmd_pool);
+       else
+               mempool_free(cmd, virtscsi_cmd_pool);
 }
 
 static void virtscsi_ctrl_done(struct virtqueue *vq)
@@ -311,21 +312,22 @@ out:
 static int virtscsi_tmf(struct virtio_scsi *vscsi, struct virtio_scsi_cmd *cmd)
 {
        DECLARE_COMPLETION_ONSTACK(comp);
-       int ret;
+       int ret = FAILED;
 
        cmd->comp = ∁
-       ret = virtscsi_kick_cmd(vscsi, vscsi->ctrl_vq, cmd,
-                              sizeof cmd->req.tmf, sizeof cmd->resp.tmf,
-                              GFP_NOIO);
-       if (ret < 0)
-               return FAILED;
+       if (virtscsi_kick_cmd(vscsi, vscsi->ctrl_vq, cmd,
+                             sizeof cmd->req.tmf, sizeof cmd->resp.tmf,
+                             GFP_NOIO) < 0)
+               goto out;
 
        wait_for_completion(&comp);
-       if (cmd->resp.tmf.response != VIRTIO_SCSI_S_OK &&
-           cmd->resp.tmf.response != VIRTIO_SCSI_S_FUNCTION_SUCCEEDED)
-               return FAILED;
+       if (cmd->resp.tmf.response == VIRTIO_SCSI_S_OK ||
+           cmd->resp.tmf.response == VIRTIO_SCSI_S_FUNCTION_SUCCEEDED)
+               ret = SUCCESS;
 
-       return SUCCESS;
+out:
+       mempool_free(cmd, virtscsi_cmd_pool);
+       return ret;
 }
 
 static int virtscsi_device_reset(struct scsi_cmnd *sc)