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Re: [Qemu-devel] [PATCH 1/2] ivshmem: check ivshmem_read() size argument


From: Peter Maydell
Subject: Re: [Qemu-devel] [PATCH 1/2] ivshmem: check ivshmem_read() size argument
Date: Mon, 14 Apr 2014 16:33:52 +0100

On 31 March 2014 08:08, Stefan Hajnoczi <address@hidden> wrote:
> The third argument to the fd_read() callback implemented by
> ivshmem_read() is the number of bytes, not a flags field.  Fix this and
> check we received enough bytes before accessing the buffer pointer.
>
> Cc: Cam Macdonell <address@hidden>
> Reported-by: Sebastian Krahmer <address@hidden>
> Signed-off-by: Stefan Hajnoczi <address@hidden>
> ---
>  hw/misc/ivshmem.c | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
>
> diff --git a/hw/misc/ivshmem.c b/hw/misc/ivshmem.c
> index 8d144ba..78363ce 100644
> --- a/hw/misc/ivshmem.c
> +++ b/hw/misc/ivshmem.c
> @@ -420,13 +420,18 @@ static void increase_dynamic_storage(IVShmemState *s, 
> int new_min_size) {
>      }
>  }
>
> -static void ivshmem_read(void *opaque, const uint8_t * buf, int flags)
> +static void ivshmem_read(void *opaque, const uint8_t * buf, int size)
>  {
>      IVShmemState *s = opaque;
>      int incoming_fd, tmp_fd;
>      int guest_max_eventfd;
>      long incoming_posn;
>
> +    if (size < sizeof(incoming_posn)) {
> +        IVSHMEM_DPRINTF("short read of %d bytes\n", size);
> +        return;
> +    }
> +

Looking at the qemu-chr API I'm not sure this is correct:
aren't we going to throw away data here? My guess is that we
need to save the half-a-word so we can use it when the
other half arrives in a subsequent call.

thanks
-- PMM



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