On Tue, Mar 26, 2024 at 02:39:27PM +0100, Stefano Garzarella wrote:
> In vu_message_write() we use sendmsg() to send the message header,
> then a write() to send the payload.
>
> If sendmsg() fails we should avoid sending the payload, since we
> were unable to send the header.
>
> Discovered before fixing the issue with the previous patch, where
> sendmsg() failed on macOS due to wrong parameters, but the frontend
> still sent the payload which the backend incorrectly interpreted
> as a wrong header.
>
> Signed-off-by: Stefano Garzarella <sgarz...@redhat.com>
> ---
> subprojects/libvhost-user/libvhost-user.c | 5 +++++
> 1 file changed, 5 insertions(+)
>
> diff --git a/subprojects/libvhost-user/libvhost-user.c
> b/subprojects/libvhost-user/libvhost-user.c
> index 22bea0c775..a11afd1960 100644
> --- a/subprojects/libvhost-user/libvhost-user.c
> +++ b/subprojects/libvhost-user/libvhost-user.c
> @@ -639,6 +639,11 @@ vu_message_write(VuDev *dev, int conn_fd, VhostUserMsg
> *vmsg)
> rc = sendmsg(conn_fd, &msg, 0);
> } while (rc < 0 && (errno == EINTR || errno == EAGAIN));
>
> + if (rc <= 0) {
Is rejecting a 0 return value correct? Technically, a 0 return means
a successful write of 0 bytes - but then again, it is unwise to
attempt to send an fd or other auxilliary ddata without at least one
regular byte, so we should not be attempting a write of 0 bytes. So I
guess this one is okay, although I might have used < instead of <=.
> + vu_panic(dev, "Error while writing: %s", strerror(errno));
> + return false;
> + }
At any rate, noticing the error is the correct thing to do.
> +
> if (vmsg->size) {
> do {
> if (vmsg->data) {
> --
> 2.44.0
>
--
Eric Blake, Principal Software Engineer
Red Hat, Inc.
Virtualization: qemu.org | libguestfs.org
