From: Jens Axboe <axboe@kernel.dk>
Date: Mon, 13 Sep 2021 19:08:51 +0000 (-0600)
Subject: io_uring: pin SQPOLL data before unlocking ring lock
X-Git-Url: http://git.maquefel.me/?a=commitdiff_plain;h=41d3a6bd1d37149b18331fc4bb789c5456a7aeb0;p=linux.git

io_uring: pin SQPOLL data before unlocking ring lock

We need to re-check sqd->thread after we've dropped the lock. Pin
the sqd before doing the lockdep lock dance, and check if the thread
is alive after that. It's either NULL or alive, as the SQPOLL thread
cannot exit without holding the same sqd->lock.

Reported-and-tested-by: syzbot+337de45f13a4fd54d708@syzkaller.appspotmail.com
Fixes: fa84693b3c89 ("io_uring: ensure IORING_REGISTER_IOWQ_MAX_WORKERS works with SQPOLL")
Signed-off-by: Jens Axboe <axboe@kernel.dk>
---

diff --git a/fs/io_uring.c b/fs/io_uring.c
index 66a7414c37568..a864a94364c6c 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -10563,10 +10563,12 @@ static int io_register_iowq_max_workers(struct io_ring_ctx *ctx,
 			 * ordering. Fine to drop uring_lock here, we hold
 			 * a ref to the ctx.
 			 */
+			refcount_inc(&sqd->refs);
 			mutex_unlock(&ctx->uring_lock);
 			mutex_lock(&sqd->lock);
 			mutex_lock(&ctx->uring_lock);
-			tctx = sqd->thread->io_uring;
+			if (sqd->thread)
+				tctx = sqd->thread->io_uring;
 		}
 	} else {
 		tctx = current->io_uring;
@@ -10580,16 +10582,20 @@ static int io_register_iowq_max_workers(struct io_ring_ctx *ctx,
 	if (ret)
 		goto err;
 
-	if (sqd)
+	if (sqd) {
 		mutex_unlock(&sqd->lock);
+		io_put_sq_data(sqd);
+	}
 
 	if (copy_to_user(arg, new_count, sizeof(new_count)))
 		return -EFAULT;
 
 	return 0;
 err:
-	if (sqd)
+	if (sqd) {
 		mutex_unlock(&sqd->lock);
+		io_put_sq_data(sqd);
+	}
 	return ret;
 }