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Subject[PATCH 5.4 27/92] io_uring: ensure req->submit is copied when req is deferred
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From: Jens Axboe <axboe@kernel.dk>

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>

---
fs/io_uring.c | 9 +++++----
1 file changed, 5 insertions(+), 4 deletions(-)

--- 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_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);
@@ -2425,7 +2426,7 @@ 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);
@@ -2452,7 +2453,7 @@ static int io_queue_link_head(struct io_
* 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);

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