From: Roger Pau Monne roger.pau@citrix.com
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@citrix.com Cc: stable@vger.kernel.org Reviewed-by: Jan Beulich jbeulich@suse.com Reviewed-by: Juergen Gross jgross@suse.com Signed-off-by: Juergen Gross jgross@suse.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- 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 @@ -685,6 +685,7 @@ 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);