From: Roger Pau Monne <roger.pau@xxxxxxxxxx>
commit 107866a8eb0b664675a260f1ba0655010fac1e08 upstream.
Do this in order to prevent the task from being freed if the thread
returns (which can be triggered by the frontend) before the call to
kthread_stop done as part of the backend tear down. Not taking the
reference will lead to a use-after-free in that scenario. Such
reference was taken before but dropped as part of the rework done in
2ac061ce97f4.
Reintroduce the reference taking and add a comment this time
explaining why it's needed.
This is XSA-374 / CVE-2021-28691.
Fixes: 2ac061ce97f4 ('xen/netback: cleanup init and deinit code')
Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
Reviewed-by: Juergen Gross <jgross@xxxxxxxx>
Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
drivers/net/xen-netback/interface.c | 6 ++++++
1 file changed, 6 insertions(+)
--- a/drivers/net/xen-netback/interface.c
+++ b/drivers/net/xen-netback/interface.c
@@ -684,6 +684,7 @@ static void xenvif_disconnect_queue(stru
{
if (queue->task) {
kthread_stop(queue->task);
+ put_task_struct(queue->task);
queue->task = NULL;
}
@@ -745,6 +746,11 @@ int xenvif_connect_data(struct xenvif_qu
if (IS_ERR(task))
goto kthread_err;
queue->task = task;
+ /*
+ * Take a reference to the task in order to prevent it from being freed
+ * if the thread function returns before kthread_stop is called.
+ */
+ get_task_struct(task);
task = kthread_run(xenvif_dealloc_kthread, queue,
"%s-dealloc", queue->name);
