[PATCH] io_uring/net: save msghdr->msg_control for retries

Jens Axboe
2023-06-12T19:56:40Z

If the application sets ->msg_control and we have to later retry this
command, or if it got queued with IOSQE_ASYNC to begin with, then we
need to retain the original msg_control value. This is due to the net
stack overwriting this field with an in-kernel pointer, to copy it
in. Hitting that path for the second time will now fail the copy from
user, as it's attempting to copy from a non-user address.

Link: https://github.com/axboe/liburing/issues/880
Signed-off-by: Jens Axboe <axboe@kernel.dk>

---

diff --git a/io_uring/net.c b/io_uring/net.c
index 89e839013837..51b0f7fbb4f5 100644
--- a/io_uring/net.c
+++ b/io_uring/net.c
@@ -65,6 +65,7 @@ struct io_sr_msg {
u16 addr_len;
u16 buf_group;
void __user *addr;
+ void __user *msg_control;
/* used only for send zerocopy */
struct io_kiocb *notif;
};
@@ -195,11 +196,15 @@ static int io_sendmsg_copy_hdr(struct io_kiocb *req,
struct io_async_msghdr *iomsg)
{
struct io_sr_msg *sr = io_kiocb_to_cmd(req, struct io_sr_msg);
+ int ret;

iomsg->msg.msg_name = &iomsg->addr;
iomsg->free_iov = iomsg->fast_iov;
- return sendmsg_copy_msghdr(&iomsg->msg, sr->umsg, sr->msg_flags,
+ ret = sendmsg_copy_msghdr(&iomsg->msg, sr->umsg, sr->msg_flags,
&iomsg->free_iov);
+ /* save msg_control as sys_sendmsg() overwrites it */
+ sr->msg_control = iomsg->msg.msg_control;
+ return ret;
}

int io_send_prep_async(struct io_kiocb *req)
@@ -297,6 +302,7 @@ int io_sendmsg(struct io_kiocb *req, unsigned int issue_flags)

if (req_has_async_data(req)) {
kmsg = req->async_data;
+ kmsg->msg.msg_control = sr->msg_control;
} else {
ret = io_sendmsg_copy_hdr(req, &iomsg);
if (ret)

--
Jens Axboe