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xen-netback: take a reference to the RX task thread

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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
2ac061ce97.

Reintroduce the reference taking and add a comment this time
explaining why it's needed.

This is XSA-374 / CVE-2021-28691.

Fixes: 2ac061ce97 ('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>
This commit is contained in:
Roger Pau Monne 2021-06-07 15:13:15 +02:00 committed by Greg Kroah-Hartman
parent 316de9a88c
commit 6b53db8c4c
1 changed files with 6 additions and 0 deletions
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6
drivers/net/xen-netback/interface.c
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@ -685,6 +685,7 @@ static void xenvif_disconnect_queue(struct xenvif_queue *queue)
{
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_queue *queue,
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);