Subject: Re: [PATCH v2] macvlan: validate flags

From: John Fastabend <[email-masked]>
Date: Thu, 01 Aug 2013 10:24:19 -0700

On 8/1/2013 9:09 AM, Michael S. Tsirkin wrote:
> commit df8ef8f3aaa6692970a436204c4429210addb23a
>      macvlan: add FDB bridge ops and macvlan flags
> added a flags field to macvlan, which can be
> controlled from userspace.
> The idea is to make the interface future-proof
> so we can add flags and not new fields.
>
> However, flags value isn't validated, as a result,
> userspace can't detect which flags are supported.
>
> Cc: "David S. Miller" <[email-masked]>
> Cc: John Fastabend <[email-masked]>
> Signed-off-by: Michael S. Tsirkin <[email-masked]>
> ---
>
> Changes from v1:
> 	tweaked commit message
> 	no code changes
>
> Please consider this patch for -stable.
>
> The idea is by the time we add more flags,
> everyone has updated to a kernel that
> detects errors, so userspace will be able
> to detect supported flags cleanly.
>

Agreed and because we haven't added more flags yet this shouldn't
break uapi. Thanks for catching this.

>
>   drivers/net/macvlan.c | 7 +++++++
>   1 file changed, 7 insertions(+)
>

By the same logic should we also add the check to macvlan_changelink()?

> diff --git a/drivers/net/macvlan.c b/drivers/net/macvlan.c
> index 18373b6..8445a94 100644
> --- a/drivers/net/macvlan.c
> +++ b/drivers/net/macvlan.c
> @@ -736,6 +736,10 @@ static int macvlan_validate(struct nlattr *tb[], struct nlattr *data[])
>   			return -EADDRNOTAVAIL;
>   	}
>
> +	if (data && data[IFLA_MACVLAN_FLAGS] &&
> +	    nla_get_u16(data[IFLA_MACVLAN_FLAGS]) & ~MACVLAN_FLAG_NOPROMISC)
> +		return -EINVAL;
> +
>   	if (data && data[IFLA_MACVLAN_MODE]) {
>   		switch (nla_get_u32(data[IFLA_MACVLAN_MODE])) {
>   		case MACVLAN_MODE_PRIVATE:
> @@ -809,6 +813,9 @@ int macvlan_common_newlink(struct net *src_net, struct net_device *dev,
>   	if (data && data[IFLA_MACVLAN_FLAGS])
>   		vlan->flags = nla_get_u16(data[IFLA_MACVLAN_FLAGS]);
>
> +	if (vlan->flags & ~MACVLAN_FLAG_NOPROMISC)
> +		return -EINVAL;
> +

Is there really a case where newlink is called without first calling
validate? I don't think there is so the snippet here in newlink could
be dropped.

Thanks,
John