Am 04.03.2016 21:44, schrieb Willem de Bruijn:
> From: Willem de Bruijn <will...@google.com>
>
> Netdevice parameter hard_header_len is variously interpreted both as
> an upper and lower bound on link layer header length. The field is
> used as upper bound when reserving room at allocation, as lower bound
> when validating user input in PF_PACKET.
>
> Clarify the definition to be maximum header length. For validation
> of untrusted headers, add an optional validate member to header_ops.
>
> Allow bypassing of validation by passing CAP_SYS_RAWIO, for instance
> for deliberate testing of corrupt input. In this case, pad trailing
> bytes, as some device drivers expect completely initialized headers.
>
> See also http://comments.gmane.org/gmane.linux.network/401064
>
> Signed-off-by: Willem de Bruijn <will...@google.com>
> ---
> include/linux/netdevice.h | 22 ++++++++++++++++++++--
> 1 file changed, 20 insertions(+), 2 deletions(-)
>
> diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
> index 5440b7b..6d1d8f4 100644
> --- a/include/linux/netdevice.h
> +++ b/include/linux/netdevice.h
> @@ -267,6 +267,7 @@ struct header_ops {
> void (*cache_update)(struct hh_cache *hh,
> const struct net_device *dev,
> const unsigned char *haddr);
> + bool (*validate)(const char *ll_header, unsigned int len);
> };
>
> /* These flag bits are private to the generic network queueing
> @@ -1420,8 +1421,7 @@ enum netdev_priv_flags {
> * @dma: DMA channel
> * @mtu: Interface MTU value
> * @type: Interface hardware type
> - * @hard_header_len: Hardware header length, which means that this is the
> - * minimum size of a packet.
> + * @hard_header_len: Maximum hardware header length.
> *
> * @needed_headroom: Extra headroom the hardware may need, but not in all
> * cases can this be guaranteed
> @@ -2627,6 +2627,24 @@ static inline int dev_parse_header(const struct
> sk_buff *skb,
> return dev->header_ops->parse(skb, haddr);
> }
>
> +/* ll_header must have at least hard_header_len allocated */
> +static inline bool dev_validate_header(const struct net_device *dev,
> + char *ll_header, int len)
> +{
> + if (likely(len >= dev->hard_header_len))
> + return true;
> +
> + if (capable(CAP_SYS_RAWIO)) {
> + memset(ll_header + len, 0, dev->hard_header_len - len);
> + return true;
> + }
> +
> + if (dev->header_ops && dev->header_ops->validate)
> + return dev->header_ops->validate(ll_header, len);
> +
> + return false;
> +}
> +
you could use
real_len=dev->hard_header_len-len;
if (real_len < 0)
...
if (capable(CAP_SYS_RAWIO))
memset(ll_header + len, 0,real_len);
..
IMHO that makes the code more clear.
re,
wh
> typedef int gifconf_func_t(struct net_device * dev, char __user * bufptr,
> int len);
> int register_gifconf(unsigned int family, gifconf_func_t *gifconf);
> static inline int unregister_gifconf(unsigned int family)
