Re: [Qemu-devel] [PATCH v2 4/9] ccid-card-passthru: Let the chardev::read() be more generic

[Marc-André Lureau]

Hi

On Thu, Feb 14, 2019 at 9:20 PM Philippe Mathieu-Daudé
<address@hidden> wrote:
>
> Suggested-by: Paolo Bonzini <address@hidden>
> Signed-off-by: Philippe Mathieu-Daudé <address@hidden>
> ---
>  hw/usb/ccid-card-passthru.c | 10 ++++++++--
>  1 file changed, 8 insertions(+), 2 deletions(-)
>
> diff --git a/hw/usb/ccid-card-passthru.c b/hw/usb/ccid-card-passthru.c
> index 0c44b38fc2..ba7c285ded 100644
> --- a/hw/usb/ccid-card-passthru.c
> +++ b/hw/usb/ccid-card-passthru.c
> @@ -285,8 +285,14 @@ static void ccid_card_vscard_read(void *opaque, const 
> uint8_t *buf, int size)
>          card->vscard_in_hdr += hdr->length + sizeof(VSCMsgHeader);
>          hdr = (VSCMsgHeader *)(card->vscard_in_data + card->vscard_in_hdr);
>      }
> -    if (card->vscard_in_hdr == card->vscard_in_pos) {
> -        card->vscard_in_pos = card->vscard_in_hdr = 0;

Interesting, it looks like we could end in a blocking condition today.

card->vscard_in_pos - card->vscard_in_hdr could not have enough room
to process an incoming message. After filling the buffer, it would
stop reading.

> +
> +    /* Drop any messages that were fully processed.  */
> +    if (card->vscard_in_hdr > 0) {
> +        memmove(card->vscard_in_data,
> +                card->vscard_in_data + card->vscard_in_hdr,
> +                card->vscard_in_pos - card->vscard_in_hdr);
> +        card->vscard_in_pos -= card->vscard_in_hdr;
> +        card->vscard_in_hdr = 0;
>      }
>  }

At least, by moving data around, this would leave always enough space
for the header to be fully read.

But I think we should add a condition like
card->vscard_in_hdr + hdr->length + sizeof(VSCMsgHeader) <=
VSCARD_IN_SIZE, to make sure the incoming message fits in the
vscard_in_data buffer, else disconnect?

>
> --
> 2.20.1
>