From: Jens Axboe <axboe@kernel.dk>
Date: Wed, 4 Dec 2019 08:53:43 -0700
Subject: io_uring: ensure req->submit is copied when req is deferred
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Patch-mainline: Never, addressed by cleanup in mainline 5.5-rc1, patch from stable commit d123a552a2d8
References: bnc#1151927 5.3.16

There's an issue with deferred requests through drain, where if we do
need to defer, we're not copying over the sqe_submit state correctly.
This can result in using uninitialized data when we then later go and
submit the deferred request, like this check in __io_submit_sqe():

         if (unlikely(s->index >= ctx->sq_entries))
                 return -EINVAL;

with 's' being uninitialized, we can randomly fail this check. Fix this
by copying sqe_submit state when we defer a request.

Because it was fixed as part of a cleanup series in mainline, before
anyone realized we had this issue. That removed the separate states
of ->index vs ->submit.sqe. That series is not something I was
comfortable putting into stable, hence the much simpler addition.
Here's the patch in the series that fixes the same issue:

commit cf6fd4bd559ee61a4454b161863c8de6f30f8dca
Author: Pavel Begunkov <asml.silence@gmail.com>
Date:   Mon Nov 25 23:14:39 2019 +0300

    io_uring: inline struct sqe_submit

Reported-by: Andres Freund <andres@anarazel.de>
Reported-by: Tomáš Chaloupka
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Jiri Slaby <jslaby@suse.cz>
---
 fs/io_uring.c |    7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -1787,7 +1787,7 @@ static int io_poll_add(struct io_kiocb *
 }
 
 static int io_req_defer(struct io_ring_ctx *ctx, struct io_kiocb *req,
-			const struct io_uring_sqe *sqe)
+			struct sqe_submit *s)
 {
 	struct io_uring_sqe *sqe_copy;
 
@@ -1805,7 +1805,8 @@ static int io_req_defer(struct io_ring_c
 		return 0;
 	}
 
-	memcpy(sqe_copy, sqe, sizeof(*sqe_copy));
+	memcpy(&req->submit, s, sizeof(*s));
+	memcpy(sqe_copy, s->sqe, sizeof(*sqe_copy));
 	req->submit.sqe = sqe_copy;
 
 	INIT_WORK(&req->work, io_sq_wq_submit_work);
@@ -2114,7 +2115,7 @@ static int io_queue_sqe(struct io_ring_c
 {
 	int ret;
 
-	ret = io_req_defer(ctx, req, s->sqe);
+	ret = io_req_defer(ctx, req, s);
 	if (ret) {
 		if (ret != -EIOCBQUEUED) {
 			io_free_req(req);