FAILED: patch "[PATCH] io_uring: Check current->io_uring in io_uring_cancel_sqpoll" failed to apply to 5.11-stable tree

The patch below does not apply to the 5.11-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 6d042ffb598ed83e7d5623cc961d249def5b9829 Mon Sep 17 00:00:00 2001
From: Palash Oswal <[email protected]>
Date: Tue, 27 Apr 2021 18:21:49 +0530
Subject: [PATCH] io_uring: Check current->io_uring in io_uring_cancel_sqpoll

syzkaller identified KASAN: null-ptr-deref Write in io_uring_cancel_sqpoll.

io_uring_cancel_sqpoll is called by io_sq_thread before calling io_uring_alloc_task_context. This leads to current->io_uring being NULL. io_uring_cancel_sqpoll should not have to deal with threads where current->io_uring is NULL.

In order to cast a wider safety net, perform input sanitisation directly in io_uring_cancel_sqpoll and return for NULL value of current->io_uring. This is safe since if current->io_uring isn't set, then there's no way for the task to have submitted any requests.

index 863420e184cf..81096f3b01ea 100644
@@ -9044,6 +9044,8 @@ static void io_uring_cancel_sqpoll(struct io_sq_data *sqd)
 	s64 inflight;
 	DEFINE_WAIT(wait);
 
+	if (!current->io_uring)
+		return;
 	WARN_ON_ONCE(!sqd || sqd->thread != current);
 
 	atomic_inc(&tctx->in_idle);