[PATCH 5.13] io_uring: Check current->io_uring in io_uring_cancel_sqpoll

[Palash Oswal <hello@oswalpalash.com>]

syzkaller identified KASAN: null-ptr-deref Write in
io_uring_cancel_sqpoll on v5.12

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.

Reported-by: syzbot+be51ca5a4d97f017cd50@syzkaller.appspotmail.com
Cc: stable@vger.kernel.org
Signed-off-by: Palash Oswal <hello@oswalpalash.com>
---
 fs/io_uring.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/fs/io_uring.c b/fs/io_uring.c
index dff34975d86b..eccad51b7954 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -8998,6 +8998,8 @@ static void io_uring_cancel_sqpoll(struct io_ring_ctx *ctx)
 	s64 inflight;
 	DEFINE_WAIT(wait);
 
+	if (!current->io_uring)
+		return;
 	WARN_ON_ONCE(!sqd || ctx->sq_data->thread != current);
 
 	atomic_inc(&tctx->in_idle);
-- 
2.27.0