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

From: "Michael S. Tsirkin" <[email-masked]>
Date: Thu, 1 Aug 2013 22:19:57 +0300

On Thu, Aug 01, 2013 at 10:24:19AM -0700, John Fastabend wrote:
> 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()?

I'm not sure what do you mean "By the same logic" -
macvlan_changelink is static unlike macvlan_common_newlink
which is exported to modules.
So why isn't macvlan_validate sufficient for 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

It seems so - macvtap_newlink calls macvlan_common_newlink.
macvtap does not seem to have .validate.