[dpdk-dev] [PATCH v2] net/af_packet: fix vlan_insert corruption

[Bruce Richardson]

On Tue, Apr 16, 2019 at 10:37:07AM +0100, Ferruh Yigit wrote:
> On 4/12/2019 11:08 PM, Stephen Hemminger wrote:
> > On Fri, 12 Apr 2019 17:28:17 +0100
> > Ferruh Yigit <ferruh.yigit at intel.com> wrote:
> > 
> >> On 4/8/2019 5:41 PM, Stephen Hemminger wrote:
> >>> If the af_packet transmit is sending a VLAN packet,
> >>> and the transmit path to the kernel os full, then it would
> >>> mismanage the outgoing mbuf. The original mbuf would end up
> >>> being freed twice, once by AF_PACKET PMD and once by caller.  
> >>
> >> This comment is valid with your new patch [1] that updates 'rte_vlan_insert()'
> >> to duplicate the mbuf, right?
> >>
> >> That patch looks like won't make the release, so I suggest this one wait that
> >> patch, although this is harmless on its own, commit log is misleading.
> >>
> >> [1]
> >> https://patches.dpdk.org/patch/51870/
> > 
> > It was always true, even with existing vlan_insert.
> > Existing vlan_insert has issues if it ever creates a clone packet.
> > Existing vlan_insert can duplicate mbuf through clone
> > 
> 
> Right, existing vlan_insert has same issue on af_packet.
> 
> But, should vlan_insert try to duplicate the mbuf when it is shared, does it
> worth the complexity it brings? And when that support removed this patch won't
> be needed.

I don't think vlan insert or other mbuf manipulation APIs should be
checking for shared state or not - that's the job of the app. We could have
cases where the user does want to modify a shared mbuf.

Regards,
/Bruce