[PATCH 5.10 491/491] io_uring/poll: correctly handle io_poll_add() return value on update

Greg Kroah-Hartman
2026-04-13T17:04:12Z

From: Jens Axboe <axboe@kernel.dk>

Commit 84230ad2d2afbf0c44c32967e525c0ad92e26b4e upstream.

When the core of io_uring was updated to handle completions
consistently and with fixed return codes, the POLL_REMOVE opcode
with updates got slightly broken. If a POLL_ADD is pending and
then POLL_REMOVE is used to update the events of that request, if that
update causes the POLL_ADD to now trigger, then that completion is lost
and a CQE is never posted.

Additionally, ensure that if an update does cause an existing POLL_ADD
to complete, that the completion value isn't always overwritten with
-ECANCELED. For that case, whatever io_poll_add() set the value to
should just be retained.

Cc: stable@vger.kernel.org
Fixes: 97b388d70b53 ("io_uring: handle completions in the core")
Reported-by: syzbot+641eec6b7af1f62f2b99@syzkaller.appspotmail.com
Tested-by: syzbot+641eec6b7af1f62f2b99@syzkaller.appspotmail.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
io_uring/io_uring.c | 26 +++++++++++++++++++-------
1 file changed, 19 insertions(+), 7 deletions(-)

--- a/io_uring/io_uring.c
+++ b/io_uring/io_uring.c
@@ -5980,7 +5980,7 @@ static int io_poll_add_prep(struct io_ki
return 0;
}

-static int io_poll_add(struct io_kiocb *req, unsigned int issue_flags)
+static int __io_poll_add(struct io_kiocb *req, unsigned int issue_flags)
{
struct io_poll_iocb *poll = &req->poll;
struct io_poll_table ipt;
@@ -5992,11 +5992,21 @@ static int io_poll_add(struct io_kiocb *
if (!ret && ipt.error)
req_set_fail(req);
ret = ret ?: ipt.error;
- if (ret)
+ if (ret > 0) {
__io_req_complete(req, issue_flags, ret, 0);
+ return ret;
+ }
return 0;
}

+static int io_poll_add(struct io_kiocb *req, unsigned int issue_flags)
+{
+ int ret;
+
+ ret = __io_poll_add(req, issue_flags);
+ return ret < 0 ? ret : 0;
+}
+
static int io_poll_update(struct io_kiocb *req, unsigned int issue_flags)
{
struct io_ring_ctx *ctx = req->ctx;
@@ -6012,6 +6022,7 @@ static int io_poll_update(struct io_kioc
ret = preq ? -EALREADY : -ENOENT;
goto out;
}
+ preq->result = -ECANCELED;
spin_unlock(&ctx->completion_lock);

if (req->poll_update.update_events || req->poll_update.update_user_data) {
@@ -6024,16 +6035,17 @@ static int io_poll_update(struct io_kioc
if (req->poll_update.update_user_data)
preq->user_data = req->poll_update.new_user_data;

- ret2 = io_poll_add(preq, issue_flags);
+ ret2 = __io_poll_add(preq, issue_flags);
/* successfully updated, don't complete poll request */
if (!ret2)
goto out;
+ preq->result = ret2;
+
}
- req_set_fail(preq);
- io_req_complete(preq, -ECANCELED);
+ if (preq->result < 0)
+ req_set_fail(preq);
+ io_req_complete(preq, preq->result);
out:
- if (ret < 0)
- req_set_fail(req);
/* complete update request, we're done with it */
io_req_complete(req, ret);
io_ring_submit_unlock(ctx, !(issue_flags & IO_URING_F_NONBLOCK));