io_uring/msg_ring: let target know allocated index

commit 555f426c0eee43e4a5f8e011f0a20aa896462278 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: 08835f2466589 ("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 7d5b544cfc305ce78a6fb32a9994306aa2b440d0..3526389ac2180b9805a5271c279572393a418282 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);