Re: [PATCH net v2] ip_gre: Reject enabling collect metadata through changelink

[Ido Schimmel]

On Mon, Sep 21, 2026 at 11:18:59AM +0800, Xuanqiang Luo wrote:
> From: Xuanqiang Luo <luoxuanqiang@xxxxxxxxxx>
> 
> ipgre_netlink_parms() can enable collect_md on an existing GRE, GRETAP
> or ERSPAN device. Unlike newlink, changelink does not enforce metadata
> tunnel uniqueness. Converting a non-metadata device can therefore
> replace the metadata receive entry for another device of the same type
> in the same netns. Deleting either device then clears the shared entry,
> breaking metadata receive lookup for the surviving device.
> 
> If parameter validation fails after collect_md is set, deleting the
> modified device can also clear an entry it never owned.
> 
> Reject enabling metadata mode in both changelink callbacks before any
> encapsulation or tunnel parameters are modified. Allow requests that
> repeat the metadata attribute on an existing metadata device.
> 
> Fixes: 2e15ea390e6f ("ip_gre: Add support to collect tunnel metadata.")
> Signed-off-by: Xuanqiang Luo <luoxuanqiang@xxxxxxxxxx>

Reviewed-by: Ido Schimmel <idosch@xxxxxxxxxx>

NL_SET_ERR_MSG_ATTR() would have been better, but I don't think it
warrants a v3.