io_uring/msg_ring: let target know allocated index

commit 5da28edd7bd5518f97175ecea77615bb729a7a28 upstream.

msg_ring requests transferring files support auto index selection via
IORING_FILE_INDEX_ALLOC, however they don't return the selected index
to the target ring and there is no other good way for the userspace to
know where is the receieved file.

Return the index for allocated slots and 0 otherwise, which is
consistent with other fixed file installing requests.

Cc: stable@vger.kernel.org # v6.0+
Fixes: e6130eba8a848 ("io_uring: add support for passing fixed file descriptors")
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://github.com/axboe/liburing/issues/809
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/io_uring/msg_ring.c b/io_uring/msg_ring.c
index 7d5b544..3526389 100644 (file)
--- a/io_uring/msg_ring.c
+++ b/io_uring/msg_ring.c
@@ -84,6 +84,8 @@ static int io_msg_send_fd(struct io_kiocb *req, unsigned int issue_flags)
        struct file *src_file;
        int ret;
 
+       if (msg->len)
+               return -EINVAL;
        if (target_ctx == ctx)
                return -EINVAL;
        if (target_ctx->flags & IORING_SETUP_R_DISABLED)
@@ -120,7 +122,7 @@ static int io_msg_send_fd(struct io_kiocb *req, unsigned int issue_flags)
         * completes with -EOVERFLOW, then the sender must ensure that a
         * later IORING_OP_MSG_RING delivers the message.
         */
-       if (!io_post_aux_cqe(target_ctx, msg->user_data, msg->len, 0, true))
+       if (!io_post_aux_cqe(target_ctx, msg->user_data, ret, 0, true))
                ret = -EOVERFLOW;
 out_unlock:
        io_double_unlock_ctx(ctx, target_ctx, issue_flags);