io_uring: ensure req->submit is copied when req is deferred

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>

diff --git a/fs/io_uring.c b/fs/io_uring.c
index b75c292..a340147 100644 (file)
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -2039,7 +2039,7 @@ add:
 }
 
 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;
 
@@ -2057,7 +2057,8 @@ static int io_req_defer(struct io_ring_ctx *ctx, struct io_kiocb *req,
                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);
@@ -2425,7 +2426,7 @@ static int io_queue_sqe(struct io_ring_ctx *ctx, struct io_kiocb *req,
 {
        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);
@@ -2452,7 +2453,7 @@ static int io_queue_link_head(struct io_ring_ctx *ctx, struct io_kiocb *req,
         * list.
         */
        req->flags |= REQ_F_IO_DRAIN;
-       ret = io_req_defer(ctx, req, s->sqe);
+       ret = io_req_defer(ctx, req, s);
        if (ret) {
                if (ret != -EIOCBQUEUED) {
                        io_free_req(req);