Re: [Qemu-devel] [PATCH] e1000: Avoid infinite loop in processing transmit descriptor

[Thomas Huth <thuth@redhat.com>]

On 04/09/15 18:21, Stefan Hajnoczi wrote:
> From: P J P <pjp@fedoraproject.org>
> 
> While processing transmit descriptors, it could lead to an infinite
> loop if 'bytes' was to become zero; Add a check to avoid it.
> 
> [The guest can force 'bytes' to 0 by setting the hdr_len and mss
> descriptor fields to 0.
> --Stefan]

I wonder whether we should log an LOG_GUEST_ERROR in that case since
this sounds like a problem in the guest ... ?

> diff --git a/hw/net/e1000.c b/hw/net/e1000.c
> index 5c6bcd0..09c9e9d 100644
> --- a/hw/net/e1000.c
> +++ b/hw/net/e1000.c
> @@ -740,7 +740,8 @@ process_tx_desc(E1000State *s, struct e1000_tx_desc *dp)
>                  memmove(tp->data, tp->header, tp->hdr_len);
>                  tp->size = tp->hdr_len;
>              }
> -        } while (split_size -= bytes);
> +            split_size -= bytes;
> +        } while (bytes && split_size);
>      } else if (!tp->tse && tp->cptse) {
>          // context descriptor TSE is not set, while data descriptor TSE is set
>          DBGOUT(TXERR, "TCP segmentation error\n");

Looks sane ... (but IMHO code would be more readable though if it would
break out of the loop already earlier, as soon as it is clear that
bytes == 0, so that e.g. the pci_dma_read(..., 0) is not called at all).

Reviewed-by: Thomas Huth <thuth@redhat.com>