io_uring/net: save msghdr->msg_control for retries

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.

Cc: stable@vger.kernel.org # 5.10+
Link: https://github.com/axboe/liburing/issues/880
Reported-and-tested-by: Marek Majkowski <marek@cloudflare.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/io_uring/net.c b/io_uring/net.c
index 89e8390..51b0f7f 100644 (file)
--- 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)